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E LEM EN TA R Y I N STJR U CT 10 N 


IN 


CHEMICAL ANALYSIS. 




ELEMENTARY INSTRUCTION 


CHEMICAL ANALYSIS. 


DR. C. REMIGIUS FRESENIUS, 

/ 


CHEMICAL ASSISTANT IN THE LABORATORY OF THE UNIVERSITY 

OF GIESSEN. 


WITH 

A PREFACE BY PROFESSOR LIEBIG. 

EDITED BY 

J. LLOYD BULLOCK, 

MEMBER OF THE CHEMICAL SOCIETY, LATE OF THE GIESSEN AND 

PARIS LABORATORIES. 



LONDON : 

JOHN CHURCHILL, PRINCES STREET, SOHO. 


MDcccxr.nr. 


ROYAL COLLEGE OF PHYSICIANS 
LIBRARY 


CLASS 


ACCN. 


SOURCE 


DATE 


U-184 


^ OF ^ 
PHYSICIANS 
OF 




LONDON: 

PRINTED BY G. J. PALMER, SAVOY STREET, STRAND. 


PREFACE 


BY PROFESSOR LIEBIG. 


Dr. Fresenius conducts the course of elementary instruction, 
in mineral analysis, in the laboratory of the University of Giessen. 
During the two last sessions lie has followed the method described 
in his work, entitled, “ Elementary Instruction in Qualitative 
Chemical Analysis.” This method I can confidently recommend 
from my own personal experience to all who are desirous of ob- 
taining instruction in inorganic analysis, for its simplicity, useful- 
ness, and tho facility with which it may bo apprehended. 

I consider Dr. Fresenius’ work extremely useful as an intro- 
duction to Professor II. Roso’s excellent manual, and for adoption 
in institutions where practical chemistry is taught, but it is espe- 
cially adapted to tho use of Pharmaceutical Chemists. 

Further, a number of experiments and discoveries have been 
recently made in our laboratory, which have enabled Dr. Fresenius 
to give many new and simplified methods of separating substances, 
which will render his work equally wclcomo to those who already 
arc familiar with the larger works on inorganic analysis. 

JUSTUS LIEBIG. 


10 



EDITOR’S PREFACE. 


This work of Dr. Freseuius has already gone through two edi- 
tions in Germany. The abundant opportunities enjoyed by its 
author of discovering the wants felt by students in entering upon 
the practice of chemical analysis, and his position in the school at 
Giessen, has enabled him to devise a method of study of the 
highest value. That it has received the approbation of the illus- 
trious head of that sohool, and the benefit of three years practical 
experience under his immediate observation, must powerfully re- 
commend it to the English student of chemistry. Whoever is 
desirous of obtaining tho knowledge necessary to become a prac- 
tical chemist, will be in no small degree indebted to Dr. Fresenius 
for the facilities thus afforded him. Every one who knows any- 
thing of Giessen, will bear testimony to the rigid economy 
of time, and the resolute adoption of every improvement in 
method which characterise that school, and serve to accomplish 
the many chemists annually flocking there for tho completion 
of their studies. The author, in his preface to tho first edition, 
tells us that he was led to compose this volume upon perceiving 
that the larger works on chemical analysis, such as H. Rose’s, 
Duflos’, and others, although admirable in themselves, present 
great difficulties to beginners, which difficulties may be summed up 


VJ 


editor's preface. 


under three heads ; 1st, Too great copiousness and detail; 2nd, 
The absence of explanations of the causes of phenomena, i. e. the 
//icon/ of the operations and reactions ; and 3rd, The omission 
altogether of many substances of very frecpient occurrence, espe- 
cially in the operations of the pharmaceutist, such as the organic 
acids, &c. 

In avoiding these objections to former works on chemical ana- 
lysis, Dr. Fresenius, 1 think, is not chargeable with having fallen 
into the opposite extreme of being too concise or elementary. 

The student may, perhaps, at first be disappointed in taking 
up this work, to find that there are no tables constructed to fur- 
nish him at a glance with all he is desirous to know of tests and 
reactions, and to save him, as he may think, trouble and 
time. But this has not arisen from oversight ; the question of 
the advantage or disadvantage of tables to the student has been 
fully considered, and the author has decided, — and the decision is 
homo out by the liighest authorities, — that such tables serve no 
really good purpose; they rather, on the contrary, supply but 
very superficial information, and satisfy the student before they 
have really informed him. The information contained in this 
work, like every other professing to teach a practical science, 
requires application and perseverance to attain ; but if begun 
at the beginning, if the student will carefully go over the neces- 
sary preliminary facts, the examination of his tests, and the 
reaction of the simple bodies consecutively, and make himself 
master of this very simple and elementary part of the course, 
he will find few or no difficulties when entering upon the more 
elaborate, and— what might appear, without this preparation — 
complex and intricate processes of the second part, the analysis 
of compound bodies. It is altogether another question whether 
the student should or should not exercise himself and his mcmoiy 
by tabulating the results of his experiments as he proceeds ; and 


editor's preface. 


vii 

to this question we reply in the affirmative : but it must he left to 
individuals to act in this, according to their own judgment, and 
their own feeling of its necessity. 

In tho preface to the Second Edition, Dr. Fresenius tells us that 
his work has met with much success, having been adopted in the 
Pharmaceutical Institution of Bonn, &c., as well as in the labo- 
ratory of Giessen ; and that he lias improved it by many correc- 
tions and additions. 

For my own part, I may be allowed to observe that tho English 
edition was undertaken by tho express desire of Professor Liebig, 
who kindly recommended its being intrusted to my care. The 
author has supplied me with many corrections, and some addi- 
tions, and the hope is shared by us in common that it will faci- 
litate the study of analytical chemistry to the English student, 
and in every way serve to promote the interests of the science. 

J. LLOYD BULLOCK. 


22, Conduit Street, Oct. 1, 1843. 



INDEX. 


PART I. 


INTRODUCTORY COURSE OF QUALITATIVE CHEMICAL ANALYSIS. 


Page 

PRELIMINARY REMARKS. 

Definition, design, and utility of qua- 
litative chemical analysis, and con- 
ditions whereon a successful study 


of this science depends . . 1 

CHAPTER i. 

Operations, § 1 . . . 5 

1. Solution, § 2 ... 5 

2. Crystallization, § 3 . . 7 

3. Precipitation, § 4 . . . 8 

4. Filtration, § 5 . . .10 

5. Decantation, § 6 . . 11 

6. Evaporation, § 7 . . . 12 

7. Distillation, § 8 . . . 13 

8. Roasting, § 9 . . .13 

9. Sublimation, § 10 . . . 14 

10. Smelting and fluxing, § 11 . 14 

11. The use of the blow-pipe, § 12 15 

Appendix to Chapter I. 
Apparatus and utensils, § 13 . . 19 


CHAPTER H. 

Reagents, § 14 . . . .21 

A. Reagents in the humid way. 

I. General Reagents, 
a ■ Reagents principally used as simple 
solvents. 

1. Water, §15 .... 24 

2. Alcohol, § 16 . . .25 

3. Ether, § 17 . . . .25 

h. Reagents which are principally 

used as chemical solvents. 

1. Hydrochloric acid, § 18 . . 26 

2. Nitric acid, § 19 . . .27 

3. Nitro-muriatic acid, § 20 .28 

4. Acetic acid, § 21 . . .28 


Page 


5. Muriate of ammonia, § 22 . 29 

f. Reagents which sene especially to 
separate or otherwise to charac- 
terize groups of substances. 

1. Reagent papers, § 23 . . 30 

2. Sulphuric acid, § 24 - . 32 

3. Sulphuretted hydrogen, § 25 . 33 

4. Hydrosulphuret of ammonia, § 

26 34 

5. Sulphuret of potassium, § 27 35 

6. Potash, § 28 . . . .36 

7. Carbonate of potash, § 29 . 37 

8. Ammonia, § 30 . .38 

9. Carbonate of ammonia, § 31 . 39 

10. Chloride of barium, § 32 . . 40 

11. Nitrate of bary tes, § 33 . . 41 

12. Chloride of calcium, §34 . 41 

13. Nitrate of silver, § 35 . . 42 

14. Perchloride of iron, § 36 . . 43 


II. Special reagents in the humid wag. 
a. Reagents which sen'e especially 
for the detection or separation of 


individual bases. 

1. Sulphate of potash, § 37 . . 44 

2. Phosphate of soda, § 38 . . 45 

3. Neutralchromateofpotash,§39 46 

4. Cyanide of potassium, § 40 . 46 

5. Ferrocyanide of potassium, § 41 47 

6. Ferricyanide of potassium, § 42 48 

7. Hydrofluosilicic acid, § 43 . 48 

8. Oxalic acid, § 44 . . . 50 

9. Oxalate of ammonia, § 45 . 50 

10. Tartaric acid, § 46 . . 51 

11 . Bitartrate of potash, § 47 . 51 

12. Acetate ofbarytes, § 48 . . 51 

13. Caustic barytes, §49 . . 52 

14. Protochloride of tin, § 50 .53 

15. Chloride of gold, § 51 . . 53 


c 






X 


INDEX. 


10. Chloride of platinum, § 52 

17. Zinc, §53 . 

1 8. Iron, § 54 

19. Copper, § 55 . 
h. Special reagents which are parti 

cularly employed for the detec 
tion and separation of acids. 

1. Acetate of potash, § 56 . 

2. Caustic lime, § 57 . 

3. Sulphate of lime, § 58 . 

4. Chloride of magnesium, § 59 

5. Protosulphate of iron, § 60 

6. Solution of magnetic oxide of 

iron, § Cl . 

7. Oxide of lead, § 62 

8. Neutral acetate of lead, § 63 . 

9. Basic acetate of lead, § 64 

1 0. Hydrated oxide of bismuth, § 65 

11. Sulphate of copper, § 66 

1 2. Protonitrate of mercury, § 67 

13. Peroxide of mercury, § 68 

14. Perchloride of mercury, § 69 . 

15. Ammonio-nitrate of silver, §70 

16. Sulphurous acid, § 71 

17. Chlorine, § 72 

18. Solution of indigo, § 73 . 

19. Starch paste, § 74 . 

B. Reagents in the dry way. 

1. Fluxes andmeans of decomposition. 

1. Mixture of carbonate of soda 

and carbonate of potash, § 75 

2. Carbonate of barytes, § 76 

3. Nitrate of potash, § 77 . 

II. Blow-pipe reagents. 

1. Charcoal, § 78 

2. Carbonate of soda, § 79 . 

3. Cyanide of potassium, § 80 

4. Biborate of soda, § 81 

5. Phosphate of soda and ammonia, 

§82 

6. Protonitrate of cobalt, § 83 

CHAPTER til. 

On the relation of the various sub 
stances to reagents, § 84 


Page 


Page 

54 

d. Protoxide of cobalt . 

. 94 

55 

e. Protoxide of iron 

. 95 

55 

/. Peroxide of iron 

. 96 

55 

Fifth group, § 89 t 

. 100 


First section, § 90 . 

. 101 


a. Oxide of silver 

. 101 


b. Protoxide of mercury 

. 102 

56 

c. Oxide of lead . 

. 103 

56 

Second section, § 91 

. 105 

57 

a. Peroxide of mercury 

. 105 

57 

b. Oxide of copper 

. 107 

58 

c. Oxide of bismuth 

. 108 


d. Oxide of cadmium . 

. 109 

59 

Sixth group, § 92 . 

. Ill 

59 

First class, § 93 . 

. 112 

59 

a. Peroxide of gold 

. 112 

60 

b. Peroxide of platinum 

. 113 

60 

Second class, § 94 . 

. 114 

61 

a. Oxide of antimony . 

. 114 

62 

b. Protoxide of tin 

. 117 

62 

c. Peroxide of tin 

. 118 

63 

d. Arsenious acid 

. 120 

63 

e. Arsenic acid . 

. 129 


63 

64 

65 
65 


66 

66 

67 

68 
68 
70 

72 

73 

74 


A. Relation of the metall 
First group, § 85 . 

a. Potash 
h. Soda 
c. Ammonia 
Second group, § 86 
a. Barytes 
/<. Strontian 

c. Lime 

d. Magnesia 
Third group, § 87 . 

a. Alumina 

b. Oxide of chromium 
Fourth group, § 88 

a. Oxide of zinc 
h. Protoxide of manga 

c. Oxide of nickel 


oxides. 


76 

77 
77 

79 

80 
81 
82 
83 

83 

84 

87 

88 

89 

90 
90 

92 

93 


B 


to Reagents, 
7 irst group. 


acid 


Relations of the Acu 
§ 95 . 

I. Inorganic acids- 
First section, § 96 . 
a. Arsenious and arson 
h. Chromic acid . 

Second section, § 97 
Sulphuric acid 
Third section, § 98 
a. Phosphoric acid 
h. Boracic acid . 

c. Oxalic acid 

d. Hydrofluoric acid 
Fourth section, § 99 

a. Carbonic acid 
h. Silicic acid 
Second group of inorgai 
a. Hydrochloric acid 
h. Hydrobromic acid 
c. Hydriodic .acid 
</. Hydrocyanic acid 

e. Hydrosulphuric acid 

Third "group of the inorganic acids, 

§ 101 

a. Nitric acid . 

h. Chloric acid . 


II. Organic Acids. 
First group, § 102 . 

a. Oxalic acid 

b. Tartaric acid 

c. Paratartaric acid 

d. Citric acid 

e. Malic acid 
Second group, § 103 

a. Succinic acid . 

b. Benzoic acid . 

Third group, § 104 

a. Acetic acid 
/. Pnrmic acid 


133 


135 
135 
. 135 
. 136 
. 136 
. 138 
. 138 
. 140 
. 140 
. 142 

. 145 
. 145 
. 146 
acids, § 100 147 
. 148 
. 149 
. 150 
. 152 
. 154 


156 

156 

157 


159 

159 

159 

160 
161 
162 
165 

165 

166 
167 
167 
169 


INDEX. 


XI 


PART II. 


SYSTEMATIC COURSE OF 
Page 

Preliminary remarks on the course of 
qualitative analysis in general, and 
on the plan of this second part 
in particular .... 173 

First Section. 

PRACTICAL PROCESS. 

I. Preliminary examination, § 105 177 

A. The body under examination is 

solid 177 

1 . It is neither a pure metal nor an 

alloy 177 

2. It is a metal or an alloy . . 181 

II. The substance under examination 

is a fluid .... 182 

II. Solution of bodies, or classifica- 
tion of substances according to 
their relations to certain sol- 
vents, § 106 . . . 183 

.1 . The substance under examination 

is neither a metal nor an alloy 184 

II. The substance under examination 

is a metal or an alloy . .186 

III. Real examination. 

Compounds supposed to consist sim- 
ply of one base and one acid, or one 
metal and one metalloid. 

A. Substances soluble in water. 

Detection of the base, § 107 . 188 

Detection of the acid. 

I. Detection of inorganic acids, § 108 195 

II. Detection of organic acids, § 109 198 

B. Substances insoluble, or sparingly 

solxdde in water, but soluble in 
hydrochloric acid, nitric acid, 
or aqua regia. 

Detection of the base, § 110 . 200 

Detection of the acid. 

Detection of inorganic acids, § 111 203 

Detection of organic acids, § 112 205 

C. Substances insoluble, or sparingly 

soluble both in water and acids. 
Detection of the base and the acid, 

§113 206 

Compounds in which all the more fre- 
quently occurring bases, acids, me- 
tals, and metalloids, are supposed to 
be present. 

A. Substances both soluble and inso- 
luble in water, and soluble in hy- 
drochloric acid, or nitric acid. 

Detection of the bases, § 114 . 208 


QUALITATIVE ANALYSIS. 

Page 


I. The solution is aqueous . . 208 

Detection of silver and protoxide of 

mercury .... 209 

II. The solution is hydrochloric 211 

III. The solution is nitric . . 211 

Detection of silver . . .211 


Precipitation with sulphuretted hy- 
drogen, § 115 . . . 212 

Treating the precipitated metallic 
sulphurets with hydrosulphuret 
of ammonia . . . .213 

Detection of the oxides of the sixth 
group, arsenic, tin, antimony, 
gold, platinum, § 116 . . 215 

Treating the metallic sulphurets in- 
soluble in hydrosulphuret of am- 
monia, with nitric acid, § 117 . 219 
Detection of the oxides of the fifth 
group ; lead, bismuth, copper, 
cadmium, peroxide of mercury . 219 

Precipitation with hydrosulphuret 
of ammonia, § 118 . . 221 

Detection of the oxides of the third 
and fourth group, &c. ; alumina, 
oxide of chromium, iron, manga- 
nese, zinc, cobalt, nickel, phos- 
phates, and oxalates of the alka- 
line earths, § 118 . . .221 

Precipitation with carbonate of am- 
monia, § 119 . . . 228 

Detection of the oxides of the se- 
cond group; barytes, strontian, 
lime, §119 . . . 228 

Magnesia, § 120 . . . 230 

Detection of the oxides of the fifth 
group, §121 . . . .231 

Potash, soda .... 231 
Ammonia, § 122 . . . 232 

Detection of the acids and metalloids 233 

A. 1. Substances soluble in water. 

I. Absence of organic acids, § 123. 233 

II. Presence of organic acids, § 124 . 236 

A. 2. Substances insoluble in water, 

but soluble in hydrochloric acid 
and in nitric acid. 

I. Absence of organic acids, § 125 . 240 

II. Presence of organic acids, § 126 . 242 

B. Substances insoluble, or sparingly 

soluble both in water arid in hy- 
drocldoric acid . . .243 

Detection of the bases, acids, and 
metalloids, § 127 . . . 243 

Special method for the decomposi- 
tion of insoluble cyanides, ferro- 
cyanides, &c., § 128 . . 249 

General rules for the detection of 


XII 


INDEX. 


Page 

inorganic substances, in cases 
where organic substances are pre- 
sent, which by their colour, con- 
sistence, or other properties, im- 
pede the application of the re- 
agents, or render the phenomena 
obscure, § 129 . . . 251 

IV. Confirmatory experiments, § 130 252 

CHAPTER II. 

Explanatory notes and additions to 


the practical course . 

254 

I. Remarks on the preliminary exa- 


mination .... 

254 ] 

II. Additional remarks upon solu- 


tion, &c. .... 

255 

III. Additional remarks upon the real 


examination, from § 107 to § 129 

257 

A. General survey and explanation 


of the analytical course 

257 

a. Detection of the bases 

257 

b. Detection of the acids 

201 


B. Special and additional remarks 


upon the 

Pago 

systematic course of 

analysis . 

. 264 

To §114 . 

. 264 

To §115 . 

. 265 

To §116 . 

. 267 

To §117 . 

. 268 

To §118 . 

. 271 

To §127 . 

. 272 

To § 128 . 

. 274 


Appendix to Part 11. 

I. General scheme for a judicious ar- 

rangement of the succession in 
which substances ought to be 
analysed .... 277 

II. Table of the more frequently oc- 

curring forms and combinations 
of the substances considered in 
the present work, with especial 
regard to the classes to which 
they belong, according to their 
various degrees of solubility in 
water, &c 280 


ELEMENTARY INSTRUCTION 


IN 


QUALITATIVE CHEMICAL ANALYSIS. 


PRELIMINARY REMARKS. 

DEFINITION, DESIGN, AND UTILITY OF QUALITATIVE CHEMICAL 
ANALYSIS, AND CONDITIONS WHEREON A SUCCESSFUL STUDY 
OF THIS SCIENCE DEPENDS. 


1 Chemistry is that science which teaches us the knowledge of 
l the elements of which our earth consists, their composition and 
j I ' decomposition, and, in general, their relation to each other. A 
I i- special branch of this science is designated by the name of ana- 
ilytical chemistry, inasmuch as it has a definite object in view, viz., 
ttho analysis of compound bodies, and the determination of their 
(constituent parts. If this determination of the constituent parts 
i merely refers to their nature, the analysis is called qualitative ; 
but if the quantity of every single element is to be ascertained, 

I 1 the analysis is called quantitative. The object of the first, there- 

J fore, is to exhibit the constituent parts of an unknown substance 
in forms already known, so that these new forms admit of safe 
inferences as to the presence of the single elements. The vidue of 
_iits method depends on two circumstances, viz. it must attain 
the object in view infallibly, and in the quickest possiblo 



B 


2 


PRELIMINARY REMARKS. 


manner. Whereas, it is the object of quantitative analysis, to ex- 
hibit those elements rendered manifest by qualitative investiga- 
tion, in such fonns as admit of an exact determination of their 
amount. 

The ways and means by which these various objects are at- 
tained, differ, of course, materially from each other. The study 
of qualitative analysis must, therefore, be separated from that of 
quantitative analysis, and, as a matter of course, must precede it. 

After having thus generally defined the meaning and objects of 
qualitative analysis, we must now shortly consider, in the first 
place, the preliminary information which qualifies students to cul- 
tivate this science successfully, the rank which it occupies in 
the department of chemistry, the objects to which it extends, the 
advantages derived from it ; and, in the second place, the main 
points whereon its study is based, and the principal branches into 
which it is distributed. 

In order to enter with any prospect of success upon qualitative 
experiments, the student must previously have acquired some 
knowledge of the chemical elements, and of their most important 
combinations, as well as of the principles of chemistry generally, 
together with a certain readiness in the apprehension of chemical 
processes. This practical art demands, moreover, strict order, 
great neatness, and a certain degree of skill in manipulations. If 
the pupil combines with these qualifications a habit, in all cases 
in which phenomena contrary to experience appear, of imputing, 
first the fault to himself, or rather to the absence of some condi- 
tion or other indispensable to the success of the experiment, — and 
a firm reliance on the immutability of the laws of nature cannot 
fail to create this habit, — ho possesses every requisite to render his 
study of analytical chemistry successful. 

Now, although chemical analysis is based on general chemistry, 
and cannot be cultivated without some knowledge of the latter, 
yet, on the other hand, we must consider it also as a kind of 
corner stone, upon which the entire structure of this science rests ; 
for it is almost of equal importance for all branches of theoretical, 
ns w r cll as of practical chemistry ; and we need not expatiate here 


PRELIMINARY REMARKS. 


3 


on the utility and advantages which the physician, the apothecary, 
the mineralogist, the rational farmer, the artisan, and many others, 
derive from it. 

This alone would be a sufficient reason to recommend a thorough 
and diligent study of this science, if even its cultivation possessed 
none of those attractions which, I may safely assert, without fear 
of contradiction, it must of necessity possess for every one who 
devotes himself zealously and ardently to its acquisition. For the 
human mind is constantly striving for the attainment of truth ; it 
delights in the solution of enigmas, and where do wc meet with a 
greater variety of problems, of more or less difficult solution, than 
in the province of chemistry ? But as a problem, an enigma, for 
which, after long pondering, we can find no solution, wearies and 
discourages the mind ; so, in like manner, do all chemical in- 
vestigations, if the object in view be not attained, if our results do 
not bear the stamp of truth, — of unquestionable certainty. A half- 
knowledge is therefore, in every province of science, but prin- 
cipally here, to be considered worse than no knowledge at all, 
and the student must therefore be especially warned against a mere 
superficial cultivation of chemical analysis. 

A qualitative experiment may be made with a twofold view, viz. 
either, 1st, to prove that some definite body or other is or is not 
contained in a substance, e. g. lead in wine ; or, 2nd, to ascertain 
nil the constituents of a chemical combination or mixture. Any 
substance whatever may, of course, become the object of chemical 
analysis. 

In the present work, however, we purpose to confine ourselves 
to those elements and combinations which are employed in phar- 
macy, arts, and trades, and understand thereby the following : 

I. Bases. 

Potash, Soda, Ammonia , Barytes, Strontian, Lime, Magnesia, 
Alumina, Oxide of Chromium, Oxide of Zinc, Protoxide of 
Manganese, Protoxide of Cobalt, Oxide of Nickel, Protoxide of 
Iron, Peroxide of Iron, Oxide of Cadmium, Oxide of Lead, Oxide 

B 2 


4 


PRELIMINARY REMARKS. 


of Bismuth, Oxide of Copper, Oxide of Silver, Protoxide of Mer- 
cury, Peroxide of Mercury, Oxide of Platinum, Oxide of Gold , 
Protoxide of Tin, Peroxide of Tin, Oxide of Antimony. 

II. Acids. 

Sulphuric Acid, Nitric Acid, Phosphoric Acid, Arsenious Acid, 
Arsenic Acid, Boracic Acid, Carbonic Acid, Chromic Acid, 
Chloric Acid, Silicic Acid, Oxalic Acid, Tartaric Acid, Para- 
tartaric Acid, Citric Acid, Malic Acid, Benzoic Acid, Succinic 
Acid, Acetic Acid, Formic Acid. 

III. Salt-radicals, and non- metallic substances. 

Chlorine, Iodine, Bromine, Cya?iogen, Fluorine, Sulphur, 
Carbon. 

The study of qualitative analysis depends principally on foui- 
points, viz. 1st, on the knowledge of operations; 2nd, on that 
of reagents and of their application ; 3rd, on that of the re- 
lation of bodies to reagents; and 4th, on that of the syste- 
matic course to be pursued in every experiment. 

Chemical analysis, therefore, requires not only theoretical know- 
ledge, but also practical skill ; and it is obvious that a mere spe- 
culative study of it can no more lead to success, than experiment- 
ing at random ; but in order to obtain satisfactorily results, theory 
and practice must be combined. 


CHAPTER I. 


OPERATIONS. 

§ 1 . 

The operations of analytical and synthetical chemistry are 
essentially the same, mollified however to u certain extent, accord- 
ing to the object we have in view, and the quantities upon which 
we operate. 

The following arc the principal operations employed in qualita- 
tive investigations. 


§ 2 . 

1. SOLUTION. 

The general meaning of “ solution ’ is “ the combination” of a 
gaseous, liquid, or solid substance, with a fluid, forming a homo- 
geneous liquid. But we call the solution moro properly absorp- 
tion when the dissolved substance is gaseous ; and when liquid, the 
term mixture or intermixture is more frequently made use of. 
The term solution, in its usual and more restricted sense, is con- 
fined to the perfect union of a solid substance with a fluid. The 
more minutely we divide the substance to be dissolved, the more 
we facilitate its solution. The liquid, by means of which the 
solution is effected, is colled the solvent. We call the solution 


(; 


SOLUTION. 


chemical, if this solvent forms a chemical combination with the 
substance dissolved, simple, if no definite combination takes 
place. 

A simple solution contains the dissolved body in a free and un- 
connected state, and with all its original properties, except those 
dependent on its form and cohesion ; and when it separates from the 
solvent in the same unaltered state, as soon as the latter is with- 
drawn. Common salt dissolved in water is a familiar instance of 
a simple solution. The salt hero imparts its peculiar taste to the 
water, and on evaporating the latter, we re-obtain common salt in its 
original form. A simple solution is called saturated when the solvent 
has received as much as it can hold of the substance to be dissolved. 
But as fluids, on an average, dissolve larger quantities of a 
substance, the higher their temperature, the term saturated can 
only refer to a certain temperature, and it must be considered a 
rule, that elevation of temperature facilitates and accelerates simple 
solution. 

A chemical solution contains the substance dissolved, not in the 
same state nor with the same properties as before ; the dissolved 
body is no longer free, but intimately combined with the solvent, 
which latter has likewise lost its original properties ; the result of 
this combination has been the formation of a new body, the solu- 
tion, therefore, now manifests the properties of this newly-formed 
substance. A chemical solution too may certainly be accelerated 
by elevation of temperature, and this is indeed usually the case, as 
heat generally promotes the action of bodies upon each other. 
But the quantity of the dissolved body remains always the same, 
in proportion to a given quantity of the solvent, whatever may bo 
the difference of temperature ; their combining proportions are in- 
variable, and independent of the gradations of temperature. 

In chemical solution, the solvent and the body, on which it acts, 
have always opposite properties, and their tendency is mutually to 
neutralize these opposite properties. Further, solution ceases as 
soon as this tendency is satisfied ; if we add more of the solid 
body it remains unaltered. The solution in this case also is called 


CRYSTALLIZATION. 


7 


saturated, or more properly neutralized, and the point which de- 
notes it to be completely so, is called the point of saturation or neu- 
tralization. The substances by means of which chemical solutions 
ore effected, are, in most cases, either acids or alkalies. They all 
require, first, a simple solvent to be converted to the fluid state. 
When the opposite properties of acid and base have mutually neu- 
tralized each other, and the new combination has been formed, the 
real conversion into fluid form takes place, only, if the product of 
this new combination possesses the property of forming a simple 
solution with the liquid present : e. g. when an aqueous solution 
of acetic acid is brought into contact with oxide of lead, there 
ensues, first, a chemical combination of the acid with the oxide, 
and then a simple solution of the thereby produced acetate of lead, 
in the water of the menstruum. 

Crystallization and precipitation are the reverse of solution, 
as they havo for their object the conversion of a fluid or dissolved 
substance into the solid state. As both depend on the same cause, viz. 
on the absence of a solvent, it is impossible to assign exact limits 
to either, and in many cases they merge into each other. Wo 
must, however, consider them separately, since they essentially 
differ, as well in their extreme forms, as, in most cases, in the 
special objects we purpose to attain by their application. 

§ 3. 

2. CRYSTALLIZATION. 

We understand by the term crystallization, in a more general 
sense, every operation, every process in which bodies pass from a 
fluid to a solid state, assuming certain regular, determinate, geome- 
trical figures. But, as these figures, which we call crystals, are 
the more regular, and consequently the more perfect, the more 
slowly the operation is carried on, we always connect with the 
term “ crystallization,” the accessary idea of a slow separation, — 
of a gradual conversion to the solid state. The formation of 
crystals depends on the regular arrangement of atoms ; it can 


8 


8 


PRECIPITATION. 


only take place if these atoms possess perfect freedom of motion, 
and thus, generally, only when a substance, from the fluid or 
gaseous, changes to the solid state. Those cases, in which it is 
sufficient merely to heat or to soften a solid body, to induce 
crystallization, must be considered us exceptions, — as, e. g. 
barley-sugar becoming white and opaque, or crystallizing, when 
moistened. 

To induce crystallization, we must remove the causes of the 
fluid or guseous form of a substance. These causes, are either — 
heat alone , e. g. in metals in fusion, or solvents alone, as in an 
aqueous solution of common salt ; or both combined, as in a hot 
and saturated aqueous solution of nitre. In the first instance, we 
can obtain crystals only by cooling the substance we wish to 
crystallize; in the second only by evaporating the menstruum; 
and in the third by either of these means. The most frequently 
occurring cases of crystallization are those by means of cooling 
hot and saturated solutions. The liquors which remain after the 
separation of the crystals, are called mother waters. The term, 
amorj)hous bodies, is applied to such solid substances as have no 
crystalline form. 

We cause crystallization to take place, generally, either to ob- 
tain the substance crystallized in a solid form, or to separate it 
from other substances dissolved in the same menstruum. 


§ 4 . 

3. PRECIPITATION 

This operation differs from crystallization inasmuch as in 
precipitation the substance dissolved is converted to the solid state, 
not in a slow and gradual manner, but suddenly ; it is a matter of 
perfect indifference, as regards the application of the term preci- 
pitation to the process, whether this substance is crystalline or 
amorphous, whether it gravitates to the bottom of the vessel, or 
whether it ascends or remains suspended in the liquid. We may 
cause precipitation to take place, either, 1st, by modifying the 


precipitation. 


0 

solvent ; — thus sulphate of lime (gypsum) separates immediately 
from its solution in water, if this water, by the addition of alcohol, 
is converted into diluted alcohol ; or 2nd, by separating some sub- 
stance insoluble in the menstruum ; — thus, if ammonia be added 
to a solution of sulphate of alumina, decomposition of this latter 
salt takes place, and alumina, not being soluble in water, is preci- 
pitated. Precipitation takes place also when, by the action of 
simple or compound chemical affinity, new combinations ensue 
which are insoluble in the menstruum ; thus, oxalate of lime 
precipitates on adding oxalic acid to a solution of acetate of 
lime ; chromate of lead on mixing chromate of potash with nitrate 
of lead. In decompositions of this kind, induced by simple or 
compound affinity, one of the new combinations generally remains 
in solution, and the same is sometimes the case with the sub- 
stance separated, — thus in the instances just mentioned, the sulphate 
of ammonia, the acetic acid, and the nitrate of potash, remain in 
solution. Cases may, however, happen, where both products pre- 
cipitate, so that nothing remains in solution, e. g. when a solution 
of sulphate of magnesia is mixed with water of barytes ; or a solu 
tion of sulphate of silver with chloride of barium. 

Precipitation is applied to the same puqioses as crystallization : 
either, 1st, to obtain a substance in a solid form; or 2nd, to se- 
parate it from other substances dissolved in the same menstruum. 
But in qualitative analysis we employ this operation especially, in 
order to detect substances by the colour, and the properties and 
relations in general, which they exhibit when precipitated, cither 
alone or in combination with other substances. The solid body 
separated by this process, is called precipitate, and the substance, 
which is the immediate cause of this separation, is termed the 
precipitant. For the sake of a more particular designation, we 
apply various terms to precipitates, according to their different 
nature ; thus we distinguish crystalline, pulverulent, flocculent, 
curdy, gelatinous precipitates, &c. &c. 

The term turbid is made use of, when a precipitate is in a state 
of such minute division, and so small in quantity, that its parti- 


10 


FILTRATION. 


cles cannot be clearly distinguished, and that the fluid in which it 
is suspended merely appears troubled. We may generally pro- 
mote the separation of a precipitate by strongly agitating the 
menstruum, as well as by elevating its temperature. The vessels 
used for the purpose of precipitation, must, therefore, admit of 
either of tlieso operations. In qualitative analysis wo prin- 
cipally make use of tubes of thin glass, closed at the bottom, 
such as are usually called test-tubes, or test- cylinders. Beside 
tho advantages just mentioned, they permit the experimentalist 
closely to inspect the whole process, as well as the colour of the 
liquids and precipitates, and to experimentalize with very small 
quantities. 

Two different operations, according to circumstances, arc em- 
ployed in analysis, in order mechanically to separate a fluid from 
matter suspended therein, namely, “ Jilt ration,’ and “ decanta- 
tion 


§ 5 . 

4. FILTRATION. 

We purify liquids, by means of tliis operation, in pouring the 
fluid from which we wish to remove tire mechanically-suspended 
solid particles, on a filter, for which purpose we usually employ 
unsized paper, supported by a funnel ; for mi apparatus of this 
description allows the liquid to trickle through with ease ; and, on 
the other hand, completely retains the solid particles. We use 
smooth filter’s and plaited filters : the former, in such cases where 
the defiltrated solid substance is to be made use of; the hitter, 
when we merely wish to clear the solution. Smooth filters are 
produced by folding a circular paper doubly together, so that the 
folds form right angles. The preparation of plaited filters is moro 
properly a matter for ocular demonstration than foi description. 
In minute operations, care should be taken that the filters do not 
reach over the brim of the funnel. It is in most cases advisable 


DECANTATION. 


11 


to moisten the filter previous to use, because then, not only the 
filtration proceeds more rapidly, but the solid particles of the 
substances to be filtered are less liable to pass through the pores 
of the filter. The paper selected for the purpose of filtration, 
must be as free as possible from inorganic substances, especially 
iron and lime. It is advisable to have always two sorts on hand, 
one of greater density for the separation of very minute precipi- 
tates, and one of greater porosity for the speedy separation of 
grosser particles. The funnels must be either of glass or of porcelain. 

§ C. 

5. DECANTATION. 

This operation is frequently made use of instead of filtration, if 
the solid particles to be removed are of considerably greater spe- 
cific gravity than the liquid in which they are suspended. They 
in such cases speedily gravitate to the bottom, and are deposited 
there, so that it becomes easy, either to decant the supernatant 
liquid by simply inclining the vessel, or to remove it by means of 
a syphon. 

In such cases where we employ these operations (filtration or 
decantation) in order to obtain the solid substance out of the 
liquid in which it is suspended, we must afterwards free this sub- 
stance by repeated washing or rinsing from the liquid still ad- 
hering to it. This operation is termed edulcoration or rinsing. 
In order to edulcorate a precipitate collected on a filter, we most 
frequently make use of the syringe bottle, — a glass vessel, stopped 
with a perforated cork, into which a small glass tube is adapted, 
drawn out at the top into a fine point. If air be blown through 
this tube, into the flask, and, when the air is sufficiently com- 
pressed, the flask be reversed, so that the inner aperture of the 
tube comes under water, a minute stream of water is expelled, pe- 
culiarly adapted to the rinsing of precipitates. 

There are four operations by means of which we separate vola- 
tile substunccs from less volatile or from fixed bodies, viz. eva- 




12 


evaporation. 


TORATION, DISTILLATION, ROASTING, and SUBLIMATION. The two 
former of these operations always refer to fluids, the two latter only 
to solids. 


§ 7 . 

6. EVAPORATION. 

This is one of the most frequently-employed operations. We 
have recourse to it when a volatile fluid is to be separated from 
another less volatile, or from a fixed substance, (either fluid or 
solid,) if by this separation we only intend to obtain tins residuary 
substance, without heeding the evaporating substance. Thus, eva- 
poration serves, for instance, to remove from a saline solution 
part of its water, in order to induce the salt to crystallize, or, 
also, to remove all the water from the solution of an uncrystal- 
lizable substance, so as to obtain this latter in a solid form, &c. &c. 
The evaporating water is entirely disregarded, in either of theso 
cases, and the only object in view is to obtain in the former case 
a more concentrated fluid, and, in the latter, a dry substance. 
These objects are always attained by converting the fluid to be re- 
moved, into the gaseous state ; in ordinary cases, therefore, by ex- 
posing it to heat ; sometimes, also, by leaving the fluid for a certain 
time, in contact with the atmosphere, or in confined air, constantly 
kept dry by hygroscopic substances; or, in many cases, by placing 
the fluid in a rarified air, with the simultaneous application of 
hygroscopic substances. The heating process is conducted either 
over a free fire, (coal-fire or flame of spirits of wine,) or in the 
sand-bath, or by means of steam, (in the water-bath,) &c. &c. 
Concentrated sulphuric acid and slaked lime, and also chloride of 
calcium, are used as the cheapest and most efficient hygroscopic 
substances. The vessels used in evaporation arc of porcelain, 
glass, platinum, or silver, and have usually the shape of a shallow 
basin. 


DISTILLATION. ROASTING. 


13 


§ 8. 

7. DISTILLATION. 

This operation has for its object tho separation of a volatile 
liquid from a less volatile or fixed substance, either solid or fluid, 
and the recovery of the evaporating fluid. In order to attain this 
object, it is necessary to reconvert the liquid from the gaseous 
form in winch it evaporated into the fluid state. A distilling appa- 
ratus, therefore, consists of three parts, whether separated from 
each other or not, is quite indifferent. These three parts are, — 1st, 
a vessel in which the liquid to be distilled is heated, and thus con- 
verted into vapour ; 2nd, an apparatus in which this vapour is 
cooled again or condensed, and thus reconverted to the fluid state ; 
and 3rd, a vessel which receives the distilled fluid. In distillation on 
a small scale, we generally employ small glass retorts and receivers, 
but in the distillation of large quantities, either a metallic appa- 
ratus, — a copper still with helmet, and coudensing-tube of pewter, 
or large glass retorts. 


§ 9. 

8. ROASTINO. 

Roasting is, in a certain measure, for solid bodies, what evapo- 
ration is for fluids ; for the object to winch we apply it is, (at least 
generally,) tho separation of a volatile substance from a less vola- 
tile, or from a fixed body, merely for the purpose of purifying this 
latter residuary substance. Roasting always presupposes the ap- 
plication of a high temperature, and in this it differs from exsic- 
cation. The form or state which the volatilized substance assumes 
on cooling, is a matter of perfect indifference as to the name of 
the operation. 

This is the usual design in the application of roasting. In 
some instances, however, substances are heated merely for the 
purpose of modifying their state, without any volatilization taking 
place ; e. g. in the conversion of oxide of chromium into its in- 


1 * SUBLIMATION. SMELTING AND FLUXING. 

soluble modification, &c. &c. Crucibles are tbe vessels made use 
of in roasting. In analytical experiments we select, according to 
tbe substances to be heated, either porcelain, or platinum, or 
silver crucibles. In operations on a large scale, we employ either 
hessian or black-lead crucibles. The necessary beat we obtain 
either from a coal-fire, or in experiments on a small scale, most 
usually by means of a Berzelius spirit-lamp. 

§ 10 . 

9. SUBLIMATION 

Is that operation, whereby solid bodies are converted into 
vapours by tbe application of heat, and condensed again by cool- 
ing, to a solid state; the substance thus volatilized and rccondenscd 
is called a sublimate. Sublimation is consequently a distillation 
of solid bodies. We generally employ this process for tbe separa- 
tion of substances of different degrees of volatility. Its applica- 
tion is of the highest importance in analysis, for tbe detection of 
divers substances, e. g. of arsenic. The vessels used in sublima- 
tion are of various shapes, according to the different degrees of 
volatility of tbe substances we have to operate upon. In subli- 
mation for analytical purposes we generally employ glass tubes 
closed at both ends. 

§ 11 . 

10. SMELTING AND FLUXING. 

We designate by the term “ smelting,” the conversion of a 
solid substance into a fluid form, by the application of heat, and 
apply this operation generally to tbe purpose either of combina- 
tion or of decomposition of bodies. The term “ fluxing” is ap- 
plied to this process in such cases where a substance, either inso- 
luble or difficult of solution in water and acids, is, by being fused 
with some other body, modified or decomposed in such a manner, 
that the former or its new-formed combinations, afterwards admit of 
solution in water or acids. We employ in analysis, according to 


USE OF THE BLOW-PIPE. 


15 


circumstances, either porcelain, silver, or platina crucibles, for 
the purposes of these operations. If we are unable to produce the 
necessary degree of heat by means of a Berzelius spirit-lamp, the 
crucible containing the substance or substances to be fused, may 
be placed in a larger, hessian crucible, and this latter exposed to 
a charcoal or coke fire. 

The application of fluxing is especially required in the analysis 
of the sulphates of alkaline earths, and of many silicates. The 
flux most commonly used is carbonate of soda, or carbonate of 
potash, or, better still, a mixture of both, in equal atomic propor- 
tions, (vide § 75.) In certain cases, carbonate of barytes is used 
instead of carbonate of soda or potash, (vide § 70.) But in either 
case the operation is conducted in platina crucibles. 

We will here briefly lay down a few precautionary rules for the 
prevention of damage to the platinum vessels used in these opera- 
tions. No substance, evolving chlorine, ought to be treated in 
platinum vessels ; no nitrate of potash, caustic potash, metals, 
sulphur or sulphurets, should be fused in such vessels, nor ought 
easily deoxidizable metallic oxides, organic metallic salts, and 
phosphoric salts, to be heated therein when organic compounds are 
present. It is also detrimental to platinum crucibles ; and espe- 
cially to their covers, to expose them directly to a strong coal-fire, 
(i. e. without shielding them in larger, hessian crucibles,) because 
silicide of platinum is easily formed, in such cases, by the in- 
fluence of the ashes, and this renders the vessels brittle. 

§ 12 . 

11. THE USE OF THE BLOW-FIPE. 

The application of the blow-pipe is of the utmost importance in 
analytical chemistry. We have hero to consider, first, the neces- 
sary apparatus ; then, the manner of its application ; and, lastly, 
the results of the operation. 

A blow-pipe is a small instrument, usually made of brass. It 
was originally used by metallurgists for the purpose of soldering, 
whence it derived the name of soldering-pipe. It consists of three 


10 


USE OF THE BLOW-PIPE. 


distinct parts ; viz. 1st, a tubo through which air is blown from 
tho mouth ; 2nd, a small vessel into which this tube is ground air- 
tight ; this vessel serves to collect and retain the moisture of the 
air blown into tho tube ; and 3rd, a smaller tube, also olosely 
fitted into this vessel, forming a right angle with the large tube, 
and having a very fine aperture at its anterior extremity. The 
blow-pipe serves to conduct a fine and continuous stream of air 
into tho flame of a candle or lamp. Such a flame, under ordinary 
circumstances, presents to the eye three distinct parts; viz. 1st, a 
dark nucleus in the centre; 2nd, a luminous part surrounding 
this nucleus ; and 3rd, a kind of mantle encircling the whole 
flame, and but feebly luminous. The dark nucleus is formed by 
tho gases which the heat evolvos from the fuel ; these gases cannot 
burn, from want of oxygen. In the luminous sphere they come into 
contact with acertain quantity of oxygen, although insufficient for their 
complete combustion. The hydrogen of the carburetted hydrogen 
gases evolved, therefore, burns principally here, whilst the carbon 
separates in a state of intense white heat, and is thus the cause of 
tho luminousness of this part. In tho outer coat, the access of 
air is no longer limited, and all the gases, not yet consumed, are 
consumed there. This part of the flame is the hottest. Oxidizable 
bodies, therefore, oxidize with the greatest possible rapidity when 
placed in it, as the conditions of oxidizement are here combined, 
viz. high temperature, and an unlimited supply of oxygen. This 
part of the flame is therefore called tho oxidizing flame. But the 
contrary ensues when we place oxidized bodies having a tendency 
to yield up their oxygen, within the luminous part of the flame, 
i. e. these substances lose their oxygen, the carbon and the still 
unconsumed carburetted hydrogen withdraw it from them, and 
thus reduce them. The luminous part of the flame is there- 
fore called tho reducing flame. Now, if we conduct a fine 
stream of air into a flame, we have oxygen, not merely around 
the outward flame, but also in its interior part. Combus- 
tion takes place, therefore, in either part. But this air rushes 
with a certain vehemence into the flame, and carries forward the 
gases evolved, mixes intimately with them, and effects their com- 


USE OF THE BLOW-PIPE. 


J 7 


bustion at a certain distance from the point of the blow-pipe. This 
spot is marked by a bluish light. It is the hottest of the whole 
flame, since the combustion is most complete there, owing to the 
intimate intermixture of the air with the gases. The luminous 
part of the flame being thus surrounded on all sides by very hot 
flames, its temperature also becomes exceedingly elevated, and 
this elevation of temperature is the principal object in the appli- 
cation of the blow-pipe ; the hottest point is then, of course, some- 
what before the aperture of the blow-pipe. In this reducing 
flame many bodies fuse with ease, which remain unaltered in a 
common flame. The heat of the oxidizing flame also is consi- 
derably increased by the blow-pipe, since it becomes more con- 
centrated upon one point. 

As fuel we use either an oil-lamp, or a wax candle, or a lamp 
fed with a solution of oil of turpentine in spirits of wine. A 
common spirit-lamp does not yield, in all cases, the requisite de- 
gree of heat. 

The blowing is effected by the cheek-muscles alone, and not 
by the lungs. This way of blowing may easily be acquired by 
j practising for some time to breathe gently, with puffed up cheeks. 
If by this means the student has succeeded so far as to be able to 
continue calmly breathing in this manner, even when holding the 
! blow-pipe between his lips, nothing except a little practice will 
be required to enable him to produce a continuous, correct, and 
steady flame. 

The supports on which the substances to be examined are ex- 
iposed to the flame of the blow-pipe, are usually either charcoal, 
iplatinum wire, or platinum plate. In the choice of charcoal for 
the purpose of blow-pipe experiments, we must especially look to 
iits being thoroughly charred, because, if not so, it will split 
and throw ofl the substances placed on it. The substances to 
be examined are put into small conical cavities carved into the 
piece of charcoal by means of a pen-knife. We generally employ 
pharcoal as a support, when we want to reduce a metallic oxide, or 
o test a substance as to its fusibility. If metals are volatile in 
he heat of the reducing flame, they evaporate partly or entirely 


18 


USE OF THE BLOW-PIPE. 


during their reduction. But these metallic vapours reoxidize in 
their transit through the external flame. 

Many of them have a peculiar colour, by means of which the 
metals may he detected. The platinum wire, as well as the plati- 
num plate, should he selected rather thin. We generally make use of 
platinum wire when fusing bodies together, by means of fluxes, in 
order to ascertain their nature, by tho colour and other properties 
of the button produced. 

The blow-pipe flame is of especial importance in chemical ex- 
periments, because its effects yield immediate results. These are 
of two different kinds ; either, 1st, we obtain merely a knowledge 
of the general properties of the body, and are consequently only 
enabled to determine the class to which it belongs, i.e. we ascer- 
tain whether it is a fixed, volatile, or a fusible substance, &c. &c. ; 
or, 2nd, the phenomena we observe at once point out what special 
body we have before us. The phenomena in question, we shall 
have occasion to examine when we treat of the relation of various 
substances to reagents. 


APPENDIX TO THE FIRST CHAPTER. 


§ 13. 

APPARATUS AND UTENSILS. 

As the student cannot be supposed to know the apparatus, 
&c., necessary for chemical analysis, it may be well here to 
furnish him with a list of indispensable articles, and to point out 
the qualities they should possess, in order to guide him in their 
purchase. 

1. A Berzelius spirit-lamp. The vessel containing the spirit 
of wine should be connected with the wick by means of a narrow 
tube, to avoid explosions; — the chimney should not he too narrow 
The aperture through which the spirit of wine is poured should 
not be air-tight. 

2. A lamp-stand with moveable rings and brackets. 

3. A glass spirit-lamp with ground cover and brass wick-tube. 

4. A brass blow-pipe with a mouth-piece made of horn or 
ibone, (vide § 12.) The longer tube may be about seven inches, 
slightly varying, of course, according to the visual distance of the 
individual ; the length of the smaller tube ought to be about two 
inches. Both must be ground air-tight into the small vessel, 
which, as we have stated, (§ 12,) collects and retains the moisture 
of the air blown through the pipe. It is advisable to keep two 
small tubes at hand, one with a wider, and the other with a nar- 
rower opening. 

c 2 


UTENSILS AND APPARATUS. 


2U 


ft- A platinum crucible with ground cover ; this should not 
be too deep, in proportion to its breadth. 

6. A platinum spatula; this ought not to be selected too 
thin, and must be as clean and even as possible, and about two 
inches long and one inch in breadth. 

7. A few pieces of platinum wire, of the size of lute- 
strings, varying in length from three to four inches, and twisted 
at both ends into a small loop. It is advisable to keep these wires 
in a small glass containing water. 

H. A stand with from twelve to twenty test tubes. The 
latter may vary from four to six or eight inches in length, and 
must he of different width. They should he made of thin white 
glass, and so well annealed, that they do not crack even if boil- 
ing water he poured into them. Their brim must be quite round, 
and slightly turned down ; it ought to have no lip whatever, as 
the latter is not of the slightest use, and prevents the tube from 
being closely stopped with the finger. 

9. Several beaker glasses and small retorts of thin, well- 
annealed glass. 

10. Several porcelain evaporating dishes, and a variety 
of small torcelain crucibles. Those of the royal manufacture 
of Berlin are quite unexceptionable in shape as well as durability. 

11. Several glass funnels of various sizes. They must he 
inclined at an angle of sixty degrees, and ought to merge into 
their tube at a definite angle. 

12. A syringe bottle, capable of holding from twelve to six- 
teen ounces of water, (vide § 5.) 

13. Several glass rods and various glass tubes. The 
latter may be bent, drawn out, &c., over a Berzelius spirit-lamp. 

14. A selection of watch-glasses. 

15. A small agate mortar. 

10. Several small iron spoons. 

17. A pair of small pincers, with scissor-handles, the blades 
close together and bent at their extremity at an obtuse angle. 

These should he varnished. 


ai 


CHAPTER II. 


REAGENTS. 

§ 14 . 

Various phenomena may manifest themselves during the de- 
composition or combination of bodies. In some cases liquids 
change their colour, in others precipitates are formed, sometimes 
effervescence takes place, and sometimes deflagration, &c. Now, 
if these phenomena are very striking, and if they accompany only 
the combination or decomposition of two definite bodies, it be- 
comes evident that by means of one of these bodies the presence 
of the other may he detected and proved : e. g. if we know that a 
white precipitate, of determinate properties, is formed on mixing 
barytes with sulphuric acid, there can be no difficulty in under- 
standing that, if by adding barytes to any liquid we obtain a precipi- 
tate of these determinate properties, the conclusion must follow, 
that this liquid contains sulphuric acid. 

Those substances which indicate the presence of other bodies, 
by somewhat striking phenomena, are called reagents, on account 
of their mutual action upon each other. 

Reagents are divided into general and special, according to the 
■ object obtained by their application. By general reagents, we un- 
derstand those by means of which we determine the class or group 
i to which the substance under investigation belongs; and by 
special reagents those, by means of which we detect a single de- 
finite substance. It cannot be considered an objection to this 




REAGENTS. 


22 


classification, that the limits between these two divisions cannot 
be drawn with uny degree of exactness. I suggest it only to in- 
duce the student to keep distinctly in view his precise object, i.e. 
whether a group is to be determined or a single substance. 

The value of reagents depends on two circumstances: 1st, whe- 
ther they are characteristic ; and 2nd, whether they are sensible. 
We call a reagent characteristic, if the alteration it produces by 
the detection of the substance, the presence of which (in mixture 
or combination) we wish to ascertain, is of so distinct a character 
as to admit of no erroneous conclusion. Thus, iron is a charac- 
teristic reagent for copper, protochloride of tin for mercury, because 
the phenomena thereby produced, such as the separation of me- 
tallic copper and of globular mercury, admit of no mistake. We 
call a reagent sensible, if its action is still clearly perceptible, 
although but a very small quantity of the substance to be detected 
may be present, e. g. the action of starch upon iodine. We need 
scarcely mention that reagents must in general be chemically pure ; 
they must contain no foreign substance, but simply consist of their 
essential constituents, for their evidence cannot be relied upon if 
this be not the case. We must therefore make it a rule carefully 
to test reagents as to their purity, before we use them in experi- 
ments, no matter whether they be articles of our own production 
or of purchase. As a matter of course, in the instruction we shall 
give when treating of each reagent in particular, and of the mode 
of testing its purity, we cannot take cognizance of all those sub- 
stances with which the reagent may, accidentally, have become 
mixed, but only of those, the presence of which is probable from 
the manner of its preparation. 

One of the most common sources of mistakes in qualitative 
analysis, proceeds from missing the proper measure — the right 
quantity- — in the addition of a reagent to a substance under exa- 
mination. Such terms as “ addition in excess,” “ supersaturation,” 
&c. often induce novices erroneously to suppose that they cannot 
add too much of the reagent, and, to avoid using too small quan- 
tities, many fill a test cylinder with acid for the supersaturation 
of a few drops of an alkaline fluid, whilst yet every drop of acid 


REAGENTS. 


23 


added, after the neutralization point has once been reached, must 
be considered an excess of acid. But, on the other hand, an in- 
• sufficient addition is just as much to be avoided as a too copious 
one, since a reagent in insufficient quantity often produces pheno- 
mena quite different from those manifested when added in excess : 
e. g. chloride of mercury, when treated with a small quantity of 
sulphuretted hydrogen, gives a white precipitate; but when treated 
with sulphuretted hydrogen in excess, the precipitate is black. 
Experience has, however, proved that the most common mistake 
beginners are liable to, and which renders their operations difficult 
and uncertain, is to add the reagents in too copious quantities. 
The reason why the experiment loses thereby in certainty, is clear, 
if we recollect that all the changes effected by reagents are percep- 
tible only within certain limits, and that consequently they become 
less aud less evident, and may the easier be overlooked the more 
we approach this point by diluting the fluid. 

No definite rules can be given for avoiding this source of errors ; 
a general rule may, however, be laid down, and this even is suffi- 
cient to point out the proper measure in all, or at least in most 
cases. It is simply this : let the student always, before the appli- 
cation of a reagent, well consider to what purpose he applies it, 
and what are the phenomena he intends to produce. 

We divide reagents into two classes, according as the fluid state 
of substances, indispensable to the action of the reagents, is caused 
either by the application of heat, or by means of liquid solvents ; 

viz. 1 , Reagents in the humid uag ; and 2, Reagents in the dry 

wag. For the sake of facility and simplicity, we subdivide these 
two classes as follows : — 

A. REAGENTS IN THE HUMID WAY. 

1. General reagents. 

a. Reagents principally used as simple solvents. 

h. Reagents principally used as CHEMICAL solvents. 

c. Reagents which serve especially to separate, or otherwise to 
characterise groups of substances. 


8 


21 


W ATE It. 


II. Special reagents. 

a. Reagents which serve especially for the detection of the 
various bases. 

b. Reagents which are particularly applied to the detection of 
the various acids. 

B. REAGENTS IN THE DRY WAY. 

I. Fluxes. 

II. Blow-pipe reagents. 

A. REAGENTS IN THE HUMID WAY. 

I. General Reagents. 
a. Reagents principally used as simple solvents. 

§ 15 . 

1. WATER. (HO.) 

Preparation . — Bure water is obtained by distilling spring-water 
from a copper still, or from a glass retort. This distillation should 
not be carried beyond three-fourths of its quantity. Rain-water 
received in the open air may in most cases be substituted for dis- 
tilled water. 

Testing. — Distilled water must leave no residue on evaporation, 
and must not alter the colour of Georgina paper. Nitrate of 
silver, chloride of barium, oxalate of ammonia, and lime-water, 
should not disturb its transparency. 

Uses. — We use water * chiefly as a simple solvent for a great 
variety of substances. It has, moreover, a special application for 
the decomposition of several neutral metallic salts, giving rise to 
the formation of soluble acid, and insoluble basic compounds ; 
this is particularly the case with the salts of bismuth and the 
chloride of antimony. 

* In chemical experiments we never make use of any other but distilled 
water; whenever therefore the term “ water” occurs in the present work, 
distilled water is meant. 


alcohol, ether. 


2 5 


§ 16. 

2. ALCOHOL. (C < H 6 0 3 :: = E, O + Aq.) 

Preparation . — Two sorts of alcohol are used in chemical ana- 
lysis ; 1st, spirit of wine of 0'83 or 0'84, (spirit us vini rectifica 
tissimus of the shops;) and 2nd, absolute alcohol. The latter 
may he obtained by distilling the former, with the addition of 
fused chloride of calcium. 

Testing . — Pure alcohol must completely volatilize, and ought 
not to cause any empyreumatic smell when nibbed between the 
hands, nor should it redden litmus paper. 

Uses . — Many substances are soluble in alcohol, others remain 
insoluble. It may therefore frequently be employed for the sepa- 
ration of the former from the latter, e. g. of chloride of strontium 
from chloride of barium. We use alcohol also to precipitate from 
their aqueous solutions such substances as are insoluble in alco- 
hol, e. g. to precipitate malate of lime. We employ alcohol, 
moreover, in the production of various kinds of ether, especially 
of acetic ether, (which is so particularly characterized by its agree- 
able odour.) Alcohol serves also for the detection of various sub- 
stances which impart a characteristic tint to its dame, especially 
boracie acid, strontian, soda, and potash. 

§ 17. 

3. ETHER. (C«H s O = EO.) 

Ether has but a very limited application in the analysis of inor- 
ganic bodies. We use it in fact only to detect and isolate bromine, 
(§ 100, b.) and for this purpose commercial officinal ether is suf- 
ficiently pure and strong. 


an 


HYDROCHLORIC ACID. 


b. Reagents which are principally used as chemical solvents, 


§ 18. 

1. HYDROCHLORIC ACID. (C1H.) 

P reparation . — A mixture oi' thirteen and a half parts of oil of 
vitriol and four ports of water, when cold, is poured upon eight 
parts of common salt contained in a retort; the neck of the retort 
is then somewhat raised, and the heat of the sand-bath applied to 
the latter, as long as gas passes over. The gas evolved is by 
means of a bent tube, transmitted through twelve parts of water, 
in a glass flask, which must be constantly kept cool. In order to 
prevent the gas from receding, the tube is only permitted to dip 
about one line into the water of the receiver. If the sulphuric 
acid contains nitric acid, the gas which passes over first, (and 
which in that case contains chlorine,) must be received separately. 
The hydrochloric acid thus produced is tested as to its specific 
gravity, and diluted with water until its specific gravity is Til 
or 1T2. 

Testing . — Hydrochloric acid, used for the purposes of chemical 
analysis, must he colourless and leave no residue upon evapora- 
tion, nor ought it to discolour indigo-solution, even when heated 
with it to boiling. Chloride of barium ought not to produce any 
precipitate of barytes, neither in the highly diluted acid, (sulphuric 
acid,) nor even after having been boiled with nitric acid, (sulphurous 
acid.) Sulphuretted hydrogen must leave it unaltered. Ferrocy- 
anide of potassium must not cause any precipitate in it, nor 
even impart the slightest blue tinge to it, after neutralization 
with ammonia and subsequent addition of some acetic acid in 
excess. 

Uses . — We employ hydrochloric acid as a chemical solvent for 
a very great variety of bodies, especially for oxides and peroxides, 
(on the solution of which, chlorine is liberated,) and salts with 
weaker acids. A solution of this kind always depends on the for- 
mation of a chloride soluble in water. Muriatic acid serves also 


NITRIC ACID. 


27 


us a simple solvent for many salts, e. g. the phosphates, borates, 
and oxalates of the alkaline earths. We use it, moreover, to expel 
weaker acids from their salts ; e. g. carbonic acid, hydrosulphurio 
acid. It has also a special application in the detection and preci- 
pitation of oxide of silver, protoxide of mercury, and oxide of 
lead, (vide infra,) as well as in the detection of free ammonia, by 
producing dense white fumes with it, dependent on the formation 
of sal ammoniac, in the air. 


§ iy. 

2 NITRIC ACID. (N 0 5 .) 

Preparation . — The nitric acid of commerce almost invariably 
contains sulphuric acid nnd hydrochloric acid. In order to purify 
it for the purpose of chemical analysis, a solution of nitrate of 
silver is added to it, as long as any precipitate of chloride of silver 
is formed ; this precipitate is allowed to settle and the supernatant 
acid decanted into a retort, and distilled to within a small fraction 
of its whole amount. The distillate is then, if necessary, diluted 
with water till the acid has a specific gravity of 1'2. 

Testing . — Pure nitric acid must be colourless, and, when eva- 
porated on a platinum plate, leave no residue behind. Nitrate of 
harytes, or nitrate of silver, must not render it turbid. It is ad- 
visable to dilute the acid highly with water before the application 
of these reagents, since nitrates will be precipitated if this precau- 
tion be neglected. 

Uses . — Nitric acid serves, in the first place, as a chemical sol- 
vent for metals, oxides, sulphurets, oxygen salts, &c. Its action 
on metals and sulphurets depends on the oxidation of these bodies, 
at the expense of part of its oxygen, and on the subsequent che- 
mical solution of the thereby formed oxides, giving rise to the 
formation of nitrates. Most oxides dissolve in nitric acid, directly 
as nitrates, and the same is the case with most insoluble — (i. e. in 
water) — salts with weaker acids, the nitric acids expelling the 
latter. For many salts with stronger acids it is (like hvdrocldoric 
acid) used as a simple solvent, e. g. the phosphates of the alkaline 


28 


N1TR0-MURIATIC ACID. AQUA REGIA. ACETIC ACID. 


earths. Nitric acid serves, moreover, as tiro most common means 
of oxidation ; thus we use it, for instance, to convert protoxide .of 
iron into peroxide, to decompose hydriodic acid and the iodides, &c. 

§ 20 . 

NITRO- MURIATIC ACID. AQUA REGIA. (N 0 4 + 01.) 

Preparation . — One measure of pure nitric acid is mixed with 
from three to four measures of pure hydrochloric acid. 

Uses . — Nitric acid and hydrochloric acid decompose each other 
in such a manner as to give rise to the formation of chlorine, 
hyponitric acid, and water. This decomposition ceases as soon as 
the liquid is saturated with chlorine, hut it is resumed imme- 
diately, if this state of saturation is disturbed, by the application 
of heat, or by the chlorine combining with some other substance. 
Thus we have, in aqua regia, 1st, a continuous source of chlorine; 
and 2nd, hyponitric acid, and consequently a combination which 
has the property of readily yielding oxygen. The mixture of 
those two substances renders aqua regia the most powerful solvent 
we possess for metals, (those excepted which form insoluble com- 
pounds, with chlorine.) We use aqua regia chiefly for the solu- 
tion of gold and platinum, (both of which are insoluble in hydro- 
chloric acid alone, as well as in nitric acid alone,) and for the de- 
composition of various sulphurets, e. g. cinnabar, &c. 

§ 21 . 

4. ACETIC ACID. (C 4 H 3 0 3 = A.) 

Preparation . — Pure acetic acid is best obtained by rubbling ten 
pails of crystallized neutral acetate of lead together, with three 
pails of anhydrous sulphate of soda, pouring the mixture into a 
retort, adding a cooled mixture of two and a half parts of sulphuric 
acid, with an equal weight of water, and distilling to dryness, in a 
sand-bath. The receiver is best connected with the retort by 
means of a Liebig's condensing apparatus. 

Testing . — Pure acetic acid must leave no residue upon evapora- 


CHLORIDE OF AMMONIUM. 


2<J 


tion. Sulphuretted hydrogen, and solution of silver and of barytes, 
must not precipitate it when diluted, solution of barytes not even 
when the acetic acid has been previously boiled with nitric acid. 
Indigo solution must not be discoloured on being heated w T ith the 
acid, (vide § 101, a.) 

Uses . — The application of acetic acid in qualitative analysis is 
chiefly based upon its possessing an unequal power of solution for 
different substances, so it serves, for instance, to distinguish oxa- 
late of lime from phosphate of lime. We apply acetic acid also 
for the acidulation of liquids, when we wish to avoid the use of 
mineral acids. 

§ 22 . 

5. CHLORIDE OF AMMONIUM. (N H 4 Cl.) 

Muriate of Ammonia. 

Preparation . — The sal ammoniac of commerce may generally 
be purified for the purposes of chemical analysis by simple re- 
crystallization.^ If it contains iron, a small quantity of hydrosulphu- 
ret of ammonia must be added to the solution ; the precipitate 
formed is allowed to settle, the solution filtered, and hydrochloric 
acid added to it until a feeble acid reaction manifests itself; the 
mixture then is boiled, filtered, saturated with ammonia, and crys- 
tallized. For use as a reagent, one part of the salt is dissolved in 
eight parts of water. 

Testing . — Solution of sal ammoniac, when evaporated on a pla- 
tinum plate, must leave a residue which completely volatilizes 
upon a higher degree of heat being applied. Hydrosulphuret of 
ammonia ought not to change it. Its reaction ought to be com- 
pletely neutral. 

Uses . — We employ sal ammoniac chiefly to keep in solution 
certain oxides, e. g. protoxide of manganese, magnesia, or certain 
salts, e. g. tartrate of lime, when other oxides or salts ore preci- 
pitated by ammonia or bv some other reagents. This application 
of sal ammoniac is based on the tendency of the ammoniacal salts 
to form double combinations with other salts. Sal ammoniac also 
serves to distinguish between precipitates possessed of similar pro- 


REAGENT PAPERS. 


30 


perties, e. g. to distinguish the basic phosphate of magnesia and 
ammonia which is insoluble in sal ammoniac, from other precipi- 
tates of magnesia. We employ sal ammoniac besides to pre- 
cipitate from their solutions, various substances soluble in 
potash, and insoluble in ammonia, e. g. alumina, oxide of chro- 
mium ; for in this process the sal ammonia decomposes with tho 
potash, and chloride of potassium, water, and ammonia are formed. 
Sal ammoniac is moreover specially used to precipitate platinum 
as ammonio chloride of platinum. 


r. Reagents which serve especially to separate or otherwise to 
characterize groups of substances. 

§ 23 . 

1. REAGENT PAPERS: a. BLUE LITMUS PAPER. 

Preparation . — One part of commercial litmus is digested with 
six parts of water ; the intensely blue liquid obtained is divided 
into two parts, and the free alkali contained in the one half satu- 
rated by stirring it repeatedly with a glass rod dipped into very 
dilute sulphuric acid, until the colour exhibits a shade of red ; then 
the other blue half is added, the whole poured into a cup, and 
slips of fine unsized paper are dipped into this tincture. These 
slips are then suspended on threads for the purpose of drying. 
The colour of litmus paper must be uniform, and neither too light 
nor too dark. 

Uses. — Litmus paper serves for the detection of free acids in 
liquids, since its blue colour becomes thereby changed into red. 
It must, however, be borne in mind, that it undergoes the same 
alteration by the neutral salts of most metallic oxides. 

/3. REDDENED LITMUS PAPER. 

Preparation. — Blue litmus tincture is repeatedly stirred with a 
glass rod dipped into dilute sulphuric acid, until its colour has 
assumed a distinct shade of red. Slips of paper are then dipped 
into this tincture. They must be distinctly red when dry. 


GEORGINA PAPER. TURMERIC PAPERS. 31 

Uses'. — The blue colour of reddened litmus paper is restored by 
pure alkalies and alkaline earths, as well as by their sulphur com- 
binations, by alkaline carbonates, and also by the soluble salts of 
several other weak acids, especially of boracic acid. It serves 
therefore for the detection of these substances in general. 

y. GEORGINA PAPER. 

Preparation . — The violet coloured petals of Georgina purpurea 
are boiled in water or digested with spirits of wine, and slips of paper 
dipped into the tincture. Care should be taken to concentrate the 
liquor only to such a degree as to impart to the paper when dry, a 
fine violet-blue colour, which must not be too dark (deep.) A 
small quantity of ammonia is added to the tincture, if the colour 
is too red. 

Uses . — Georgina paper is reddened by acids ; alkalies impart a 
beautiful green tinge to it. It is therefore of very convenient ap- 
plication, as a substitute for the blue as well as the red litmus 
paper. It is of extreme susceptibility, if properly prepared, for 
acids as well as for alkalies. Concentrated solutions of caustic 
alkalies, colour it yellow by destroying its colouring matter. 

S. TURMERIC PAPER. 

Preparation . — One part of bruised turmeric-root is digested 
and heated with six parts of dilute spirit of wine ; the tincture ob- 
tained is filtered, and slips of fine paper are dipped into it. Tur- 
meric paper, when dry, must have a fine yellow colour. 

Uses . — It serves in the same manner as reddened litmus paper 
and Georgina paper, for the detection of free alkalies, &c . ; as 
they change its yellow colour into brown. It is not so susceptible 
as the other reagent papers, but the change of colour it produces 
is highly characteristic, and can be especially well perceived in 
several coloured liquids ; we consequently cannot well dispense 
with turmeric paper. It must be borne in mind, when using it as 
a test, that, besides the substances mentioned above, (vide red- 


SULPHURIC ACID. 


a 2 


dened litmus paper,) several other bodies, e. g. boracicacid, change 
its yellow colour into brown. 

All reagent papers should he cut into slips, and kept in well- 
closed glass jars or small boxes. 

§ 24. 

2. SULPHURIC ACID. (S Os.) 

English sulphuric acid may always he used in qualitative ana- 
lysis, provided it contains no arsenic, and has previously been 
freed from nitric acid, by boiling.* 

Testing. — Pure sulphuric acid, when hoiled with a small quan- 
tity of indigo solution, must not destroy its blue colour. When 
mixed with pure zinc and water, it must yield hydrogen, which, 
on being passed through a tube heated to redness, does not 
deposit the slightest crust of arsenic. (Compare § 93, d.) 

Uses . — Sulphuric acid having to most bases a greater affinity 
than almost any other acid, is principally employed for the libe- 
ration and expulsion of other acids, especially of phosphoric, 
boracic, muriatic, nitric, and acetic acids. Sulphuric acid serves 
also for the liberation of iodine from the iodides. It oxidizes, in 
this process, the metals at the expense of its own oxygen, and is 
converted into sulphurous acid. Several substances which cannot 
exist in an anhydrous state (e. g. oxalic acid) are decomposed 
wdien brought into contact with concentrated sulphuric acid ; this 
decomposition is caused by the great affinity which sulphuric acid 
has for water. The nature of the decomposed body may in such 
cases be determined by the liberated products of its decomposi- 
tion. Sulphuric acid is, moreover, frequently used for the evolu- 
tion of several gases, especially of hydrogen and sulphuretted 
hydrogen. It is besides especially employed for the detection and 
precipitation of barytes, strontian, and lead. The acid used for 
this purpose is diluted with four parts ol water. 

* The sulphuric acid of commerce often contains lead, which renders it 
turbid when diluted ; this may be removed by allowing the lead to subside, 
or by distillation. — E d. 


SULPHURETTED HYDROGEN. 


33 


§ 25. 

3. SULPHURETTED HYDROGEN. (HS.) 

Preparation . — Mix intimately thirty-two parts of iron filings 
with twenty-one parts of sublimed sulphur, divide into small por- 
tions, and gradually project them into a crucible heated to redness, 
and before adding new portions, wait until the last are red-hot. 
After the entire mixture has thus been fused, the crucible is well 
covered, and allowed to remain a short time longer exposed to the 
fire. The sulphuret of iron thus obtained is broken into lumps, 
when cool, covered with water, in an evolution bottle (a,) and 
concentrated sulphuric acid added by means of (through) a funnel 
tube ( b .) The gas evolved is transmitted through some water (c) 
for the purpose of purifying it. 




Sulphuretted hydrogen water is prepared by conducting the 
:gas obtained in the preceding process into water of the lowest pos- 
sible temperature (d) until it is saturated, consequently until the 
whole volume of the gas added in excess begins to escape com- 
pletely unabsorbed. Sulphuretted hydrogen water must he kept 
in well-closed vessels, as it soon undergoes complete decomposi- 
i^lion, if this precaution is neglected. It keeps very long if it is 
limmediatcly after preparation put into little flasks, and these 
j! latter, being well corked, are placed in an inverted position into 
small vessels filled with water. Sulphuretted hydrogen water must 

D 


34 


HYDROSULPHURET OF AMMONIA. 


be clear, possess the odour of the gas to a high degree, and yield 
a strong precipitate of sulphur, when treated with chloride of iron. 
It must not assume a blackish tinge upon the addition of ammonia. 

Uses . — Sulphuretted hydrogen has a strong tendency to decom- 
pose with metallic oxides, forming water and sulphurets. As these 
latter are mostly insoluble in water, a decomposition of this kind 
is usually attended with precipitation of the metallic oxides from 
their solutions. The conditions under which these precipitations 
take place, differ in such a manner, that by altering them we are 
enabled to divide all precipitable metals into groups, (as we shall 
afterwards explain, vide § 20, uses.) Sulphuretted hydrogen is, 
therefore, an invaluable means for the division of metals into groups. 
Some of these sulpliuret precipitates have so distinct a colour, 
that we are enabled thereby to determine the particular metals they 
contain. Sulphuretted hydrogen serves for the special detection 
of the following metals : tin, antimony, arsenic, cadmium, man- 
ganese, and zinc. For more ample information we refer the reader to 
the third chapter. From its property of being readily decomposed, 
sulphuretted hydrogen serves also as means of reduction for many 
substances ; thus, for instance, salts of peroxide of iron are con- 
verted by it into salts of protoxide of iron, chromic acid is changed 
into chromic oxide, &c. Sulphur separates in these reductions, 
in tlie form of a white powder. 

§ 26. 

2. HYDROSULPHURET OF AMMONIA. (NH 4 SIIS.) 

Preparation — This liquid is formed by transmitting sulphu- 
retted hydrogen through liquor of ammonia, to complete satura- 
tion, consequently till it no longer causes precipitation in a solu- 
tion of sulphate of magnesia. The solution obtained must be kept 
in well-closed bottles, since contact with the atmosphere decom- 
poses it 

Testing. — Hydrosulpliuret of ammonia is transparent at first, and 
yields no sulphur on being mixed with acids ; in contact with the 
atmosphere it assumes a yellow tint caused by the formation of 
sulpliuret of ammonium, in excess. This yellow tinge, however, 
does not render the reagent useless. But it now yields sulphur 


SULPHURET OF POTASSIUM. 


35 


when mixed with acids, and this ought not to be overlooked in 
experiments. Hydrosulphuret of ammonia must be transparent, 
and when heated evaporate without residue ; and, as already men- 
tioned above, ought not to precipitate solution of magnesia. 

Uses . — The arrangement into groups of the metallic oxides, 
precipitable by sulphuretted hydrogen, depends upon certain con- 
ditions indispensable to their precipitation. The presence of an 
alkali is one of these conditions — its absence is another ; i. e. cer- 
tain sulphurets precipitate only if the liquid is alkaline, because 
they are soluble in acids, others precipitate only if the liquid is 
acid, as they are soluble in alkaline sulphurets. Now, hydrosul- 
phuret of ammonia may be considered as a reagent in which sul- 
phuretted hydrogen acts in conjunction with ammonia. Here we 
have, therefore, a3 well those conditions which are necessary for 
the precipitation of the first-mentioned group, as also those con- 
ditions which prevent the precipitation of the other group of sul- 
phurets, or cause their re-solution, when those precipitated from 
acid solutions are digested with the reagent. For the purposes of 
this latter application, the hydrosulphuret of ammonia must, in 
« certiiin cases, contain sulphur in excess. Besides the sulphurets, 
the precipitation of which is effected by the joint action of sul- 
iphuretted hydrogen and of ammonia, the hydrosulphuret of am- 
monia by the solo action of its ammonia, precipitates oxide of 
chromium and alumina as hydrated oxides, and also such sub- 
stances as are only dissolved by free acids, e. g. phosphate of lime, 
dissolved in hydrochloric acid, and this property of hydrosulphuret 
of ammonia must not be lost sight of in experiments. 

§ 27. 

SULPHURET OF POTASSIUM. (KS 3 .) 

Preparation . — This reagent must not be kept in store, but pre- 
wired immediately previous to its application. It may be pro- 
duced by boiling sulphur, in proper proportions, with solution of 
•uustic potash. 

Uses . — Sulphuret of potassium must be substituted for hydro- 
ulphuret of ammonia, when sulphuret of copper is to be separated 
rom sulphur combinations soluble in alkaline sulphurets, e. g. 

D 2 


30 


POTASH. 


from sulpliuret of tin, because the sulpliuret of copper is not quite 
insoluble in hydrosulphuret of nmmonift. 

§ 28. 

0. POTASH. (KO.) 

Preparation . — One ounce of pure carbonate of potash (§ 29) 
is dissolved in twelve ounces of water, the solution boiled in a 
clean iron pan, and whilst the liquid is kept constantly at the 
boiling point, hydrate of lime added in small portions until a por 
tion of the fluid thus obtained, causes no longer any effervescence 
when filtered into hydrochloric acid. (The proportions used are, 
the hydrate of about one part of caustic lime to two parts of car- 
bonate of potash.) The pan is then taken off the fire. If the 
process has been conducted exactly according to the direction here 
given, the carbonate of lime which has been formed will quickly 
subside. When all the carbonate of lime has settled at the bottom 
of the vessel, the supernatant solution of potash may be filtered 
through bleached linen, and the filtrate obtained rapidly evaporated 
in a clean iron pan, or more properly in a silver basin, until four 
ounces only remain, which, consequently, will give a specific gra- 
vity of 3 *33. Solution of potash is kept best in small bottles, 
shut in the manner of glass spirit-lamps by a ground-glass cover, 
in default of which a small slip of paper ought to be rolled around 
the glass stopper of a common bottle. If this precaution be neg- 
lected, it will be found impossible, after a short time, to take the 
stopper off. 

Testing . — Pure solution of potash ought to be colourless. It 
must form no precipitate with chloride of barium nor with nitrate 
of silver, when supersaturated with nitric acid, during which latter 
operation a slight effervescence only ought to take place. It must 
leave no silicic acid behind, when after evaporation to dryness the 
residue is washed off with water. It ought not to be rendered 
turbid on being heated with an equal measure of solution of sal 
ammoniac. 

Uses . — By means of its great affinity for acids, potash decom 
poses the salts of most bases, and precipitates therefore from their 
solutions all those salts which are insoluble in water. Many of 


CARBONATE OF POTASH. 


37 


these oxides are dissolved by potash in excess, e g. alumina, 
oxide of chromium, oxide of lead ; others are not, e. g. oxide of 
iron, oxide of bismuth, &c. Potash thus furnishes us with a 
means of separating the former oxides from the latter. Potash, 
besides, dissolves many salts, (e. g. chromate of lead,) sulphurets 
a. s. o., and thus enables us as well to separate as to distinguish 
them from other substances. Many of the precipitates produced 
by potash exhibit particular colour or other characteristic proper 
ties, as, e. g. suboxide of manganese, suboxide of iron, suboxide 
of mercury, and by means of these colours or properties we may 
detect the nature of the metals they contain. Potash expels am- 
monia from its salts, and thus enables us to detect the latter sub- 
stance by its odour, its reaction on vegetable colours, &c. 

§ 29. 

7. CARBONATE OF POTASH. (KO C0 2 .) 

Preparation . — Pure carbonate of potash, for chemical purposes, 
is prepared by calcining purified bitartrate of potash in an iron 
pan, to complete carbonization , the residue is then boiled with 
water ; the solution thus obtained is purified by filtration and eva- 
porated to dryness, in a clean iron pan ; towards the latter end of 
this process the mass must be constantly stirred. The residuary 
dry salt is kept in a well-closed bottle. For use one part of it is 
dissolved in five parts of water. 

Testing . — Pure carbonate of potash must be perfectly white. 
Its solution, when supersaturated with nitric acid, must not 
be rendered turbid by chloride of barium nor by nitrate of silver ; 
and, when supersaturated with hydrochloric acid and evaporated 
to dryness, must leave no residue (silica) when redissolved in 
water. 

Uses . — Carbonate of potash precipitates all bases, with the ex- 
ception of the alkalies, most of them as carbonates, but also a few 
as oxides. Those bases which are soluble in w’ater, as bicarbo- 
nates, are only on boiling completely precipitated from their acid 
solutions. Many of the precipitates produced by carbonate of 
potash exhibit particular colours, and may therefore serve for 


38 


AMMONIA. 


the detection of the various metals. The solution of carbonate of 
potash is moreover employed for the decomposition of many in- 
soluble salts with metallic bases, or bases of the alkaline earths, 
especially of those with organic acids. For these salts, on being 
boiled with carbonate of potash, are converted into carbonates, 
whilst the acids combine with the potash, forming soluble salts. 
Carbonate of potash is also used to saturate free acids, in order to 
obtain them in combination with potash as salts, and is, moreover, 
especially used to precipitate platinum from solutions containing 
hydrochloric acid. 


§ 30. 


8. AMMONIA. (NH 4 0.) 




- /nL 
6 - 


Iff r 

*Z VV- 


7 


Preparation , — Pure liquor of ammonia is prepared by slaking 
four parts of quick lime with one and one-third part of water, mix- 
ing this hydrate of lime, in a glass retort, with five parts of sal 
ammoniac reduced to powder, and cautiously adding as much water ^ ? 
ns will cause the powder to form into lumps when agitated. The^Jl 
retort is then placed in a sand-bath, and brought into connexion 
with two gas conducting tubes, joined to each other in the middle 
by means of a rinsing apparatus, containing only a small quantity 
of water, such as has been described in the preparation of sulphu- 
retted hydrogen, (vide § 25, and engraving.) The absorbing re-^^ 
ceiver should contain ten parts of water. This receiver is placed 
in a vessel filled with cold water ; heat is then applied to the re- fftf n 
tort. The evolution of gas immediately ensues. The heat is con- 
tinued until no more bubbles appear, and the stopper of the retort 
is then quickly taken off, to prevent the fluid from receding. 

The liquor of ammonia contained in the washing apparatus is im- 


pure, but that in the receiver is pure ; it contains about sixteen per 
cent, of ammonia, and thus has a specific gravity of 0.93. It is 
kept in phials closed with glass stoppers. 

Testing . — Pure liquor of ammonia must be colourless, and 
upon evaporation on a watch-glass not leave the slightest residue. 
It ought not to render lime-water turbid, (carbonic acid,) and 
after super saturation with nitric acid, must not be rendered turbid 


CARBONATE OF AMMONIA. 


30 


by solution of barytes nor by solution of nitrate of silver, uor be 
coloured by sulphuretted hydrogen. 

Uses — Ammonia is one of the most frequently used reagents. 
It is especially applied for the saturation of acid liquids, for the 
precipitation of a great many metallic oxides and earths, as well 
as for their separation from each other, as many of them are dis- 
solved as ammoniacal double salts, by ammonia in excess ; such 
as the oxides of zinc, cadmium, silver, copper, nickel, and cobalt, 
whilst others remain insoluble in free ammonia. The precipitates, 
as well as their ammoniacal solutions, sometimes exhibit a very 
distinct and peculiar colour, by means of which we may at once 
detect the metals which they contain. 

Many oxides which are precipitated by ammonia from neutral 
solutions, are not precipitated from acid solutions, their precipita- 
tion being here prevented by the formation of an ammoniacal 
salt. (Compare Chloride of Ammonium, § 22.) 

§ 31. 

9. CARBONATE OF AMMONIA. (NH 4 O, C0 2 ) 

Preparation . — We use, for the purposes of chemical analysis, 
sesquicarbonate of ammonia, which must be entirely free from any 
smell of animal oil, (such as is prepared on a large scale, by the 
sublimation of sal ammoniac and chalk.) The outer and inner 
surface of the mass must be carefully scraped off ; and then one 
part of the salt dissolved in a mixture of four parts of water, and 
one part of caustic liquor of ammonia. 

Testing . — Pure carbonate of ammonia must completely evapo- 
rate, and after supersaturation with nitric acid, neither be coloured 
nor precipitated by solution of barytes, nor by solution of silver, 
nor by sulphuretted hydrogen. 

Uses . — Carbonate of ammonia precipitates most metallic oxides 
and earths, like carbonate of potash. The complete precipitation 
of many of them takes place only on boiling. Several of the pre- 
cipitated combinations redissolve again when this reagent is added 
in excess. Carbonate of ammonia dissolves many hydrates of 
oxides in a like manner, and thus enables us to separate them 


40 


CHLORIDE OF BARIUM. 


from others which are insoluble. This power of solution depends 
upon the tendency of ammoniucal salts, to form soluble double salts, 
indecomposible by free ammonia as well as by carbonate of 
ammonia. 

Like caustic ammonia, and for the same reason, carbonate of 
ammonia does not precipitate from acid solutions, many oxides 
which it precipitates from neutral solutions. (§ 30.) We apply 
carbonate of ammonia, in chemical analysis, especially for the 
precipitation of barytes, of strontian and of lime, and for the sepa- 
ration of these substances from magnesia, as the latter is not pre- 
cipitated in the presence of ammoniacal salts. 

§ 32. 

10. CHLORIDE OF BARIUM. (Ba, Cl.) 

Preparation . — Six parts of heavy spar reduced to a fine powder 
are mixed with one part of powdered charcoal and one and a half 
part of flour ; this mixture is put into a hessian crucible and ex- 
posed to the strongest possible red heat. The fused mass is rubbed 
to powder when cool ; about nine-tenths of the powder are boiled 
with four times their weight of water, and hydrochloric acid is 
added, until no more effervescence of sulphuretted hydrogen tidies 
place, and the liquid manifests an acid reaction. Then the last tenth 
of the fused mixture is added, and the boiling still continued for 
some time. The alkaline liquid is then filtered and crystallized. 
The crystals when dry are digested and washed with alcohol, 
redissolved in water, and again crystallized. For use, one part of 
the crystals is dissolved in ten parts of water. 

Testing . — Pure chloride of barium must not affect vegetable co- 
lours, nor ought its solution to be altered by sulphuretted hydrogen, 
nor by hydrosulphuret of ammonia. Pure sulphuric acid must 
precipitate every fixed particle from it, so that the filtered liquid 
leaves not the slightest residue when evaporated on a platinum 
plate. 

Uses . — Barytes forms, with many acids, soluble salts; with others, 
insoluble combinations. This property of barytes affords us a 
means of distinguishing the former acids, which ore not precipitated 


NITRATE OF BARYTES. CHLORIDE OF CALCIUM. 


4 L 








by chloride of barium, from the latter in saline solutions which 
are precipitated by chloride of barium. These barytes pre- 
cipitates manifest to other substances (acids) relations differing 
from each other. Consequently, by subjecting them to the action 
of such bodies, we may subdivide again the group of precipitable 
acids, and even directly detect certain acids. Chloride of barium 
is one of our most important reagents, on account of its applica- 
tion distinguishing one group of acids from another, and espe- 
cially as a means of detecting sulphuric acid. 


§ 33. 


11. NITRATE OF BARYTES. (Bft O, N0 4 .) 


Preparation . — A dilute solution of chloride of barium is boiled, 
and carbonate of ammonia added, as long as it causes any preci- 
pitate, and further until the liquid manifests an alkaline reaction. 
The carbonate of barytes obtained by this process is carefully 
washed, and then dissolved in hot and dilute nitric acid, until the 
liquid no longer manifests any acid reaction. The solution is 
then filtered and afterwards crystallized, by evaporation. One 
part of the crystallized salt is dissolved in ten parts of water, 
for use. The tests as to its purity are the same as in chloride 
of barium. Nitrate of silver must not render its solution 
turbid. 

Uses . — Nitrate of barytes is analogous in its action to chloride 
of barium, and may be substituted for this latter substance, when 
we wish to avoid the formation of a chloride in a liquid. 

§ 34. 

CHLORIDE OF CALCIUM. (Ca Cl.) 

Preparations. Chalk is added to hot and dilute hydrochloric 
acid, until all acid reaction ceases ; the solution is then filtered, 
and, with the addition of some ammonia, allowed to stand a few 
hours, at a moderate heat. It is then filtered again ; the filtrate 
| is heated to boiling, and carbonate of ammonia added until till 




42 


NITRATE OF SILVER. 


the lime is precipitated ; the thus obtained carbonate of lime is 
carefully washed. A mixture of one part of pure hydrochloric 
acid, with five parts of water, is then heated and the washed 
Carbonate of lime added to complete neutralization; the solu- 
tion is then boiled up several times, filtered, and preserved for 
use. 

Tenting . — Solution of chloride of calcium must be perfectly 
neutral, and neither he tinged nor precipitated by liydrosulphuret 
of ammonia; nor ought it to evolve ammonia when mixed with 
potash or with hydrate of lime. 

Use . — Chloride of calcium is, in its action and application, 
analogous to chloride of barium. For, as the latter is applied to 
divide the inorganic acids into groups, so the former serves for 
the same purpose with the organic acids, since it precipitates some 
of them, whilst it forms soluble combinations with others. And, 
as is the case with the barytes precipitates, the different conditions 
under which the various insoluble lime salts are precipitated, 
furnish us with means for a more special classification of these 
acids. 

§ 35. 

13. NITRATE OF SILVER <Ag O, NO:,.) 

Preparation . — To obtain nitrate of silver in a state of purity, 
silver alloyed with copper, as e. g. a piece of standard coin, is 
dissolved in nitric acid. The solution is evaporated to dryness, 
and the residue fused in a small porcelain crucible, at a moderate 
heat, by means of a spirit-lamp, till all the nitrate of copper is 
decomposed, i. e. till the green colour of the salt has completely 
vanished, even in the portions adhering to the upper sides of the 
crucible, and a portion dissolved in water becomes no longer blue 
when ammonia in excess is added. The mass, when cooled, is 
boiled with water, filtered, and crystallized. One part of the 
crystals is dissolved in twenty parts of water, for use. The oxide 
of copper remaining after the solution of the lused mass, always 
contains some silver, to remove which the residue is dissolved in 


CHLORIDE OF IRON. 


43 


nitric acid, and the silver precipitated from the solution, ns 
chloride of silver. 

Testing . — Nitrate of silver may be considered pure, if the fixed 
part of its solution is completely precipitated by dilute hydro- 
chloric acid, so that the fluid filtered from the chloride of silver 
leaves no residue upon evaporation on a watch-glass, and is 
neither precipitated nor tinged by sulphuretted hydrogen. 

Use . — Oxide of silver forms, with many acids, soluble, with 
others, insoluble combinations ; nitrate of silver may therefore be 
used, like chloride of barium, for the classification of acids into 
groups. 

Most of the insoluble silver combinations are soluble in dilute 
nitric acid, chloride, iodide, bromide, and cyanide of silver ex- 
cepted. Nitrate of silver is, therefore, an excellent means for 
distinguishing and separating the hydrncids corresponding to the 
last-named silver combinations from nil other acids. Nitrate of 
silver is also of great importance for the detection of individual 
acids, as many of the silver precipitates exhibit a particular 
colour, (chromate, and arseniate of silver, for example,) or a par- 
ticular relation to other reagents, or peculiar properties, on being 
heated, e. g. formiate of silver. 

§ 30. 

14. PERCIILORIDE OF IRON. (FOj Cl 3 .) 

Preparation. — To obtain pure perchloride of iron, two parts of 
hydrochloric acid, diluted with from six to eight parts of water, 
are heated with an excess of small iron nails free from rust, until 
the evolution of hydrogen ceases ; the solution is then decanted, 
mixed with one part of hydrochloric acid, boiled in a very capa- 
cious vessel, and, whilst boiling, nitric acid in small portions 
cautiously and gradually added, till a further addition pro- 
duces no longer any effervescence ; i. c. till no more red 
vapours of nitrous acid appear, and solution of ferricyanide of 
potassium (§ 42) no longer tinges the mixture blue. A small 
excess of nitric acid does no harm whatever. The solution ob- 
it) 


-I I 


SULPIIURET OF POTASH. 


tained is then diluted with water, boiled, ammonia added to alka- 
line reaction, and the produced precipitate of hydrated peroxide 
of iron well washed with hot water, and when still moist, 
added to a heated mixture of 272 parts of hydrochloric acid, and 
ten parts of water, till the last portions are not dissolved, even 
on continued heating. The solution is then filtered, and kept 
for use. 

Testing. — Solution of perchloride of iron, for the purposes of 
chemical analysis, must not contain acid in excess ; a portion of 
it must, therefore, when stirred with a small rod dipped in am- 
monia, yield a precipitate, which is not re-dissolved on shaking 
the vessel. Ferricyanide of potassium must not impart a blue 
tinge to it. 

Use . — Chloride of iron serves for a further classification of 
those organic acids which are not precipitated by chloride of 
calcium, as it produces precipitates with benzoic and succinic salts, 
whilst it leaves acetic and formic salts in solution. The neutral 
salts which these latter acids form with peroxide of iron, dissolve 
in water, imparting an intensely red colour to the latter ; chloride 
of iron affords, therefore, a useful means for their detection. 
(Vide § 98, a 7, for its application for the decomposition of 
phosphates of the alkaline earths, to which purpose it is exceed- 
ingly well adapted.) Chloride of iron serves also for the detection 
of ferrocyanide of hydrogen, producing Prussian blue with this 
substance. 

II. — SPECIAL REAGENTS IN THE HUMID WAY. 

a. Reagents which serve especially for the detection or separa- 
tion of individual bases. 

§ 37. 

1. SULPHATE OF POTASH. (KO, S0 3 .) 

Preparation. — The sulphate of potash of commerce is purified 
by re-crystallization, and one part of the pure salt is dissolved in 
twelve parts of water, for use. 


PHOSPHATE OF SODA. 


45 


Uses . — Sulphate of potash precipitates from solutions of barytes 
and strontian the sulphates of the oxides, which are insoluble in 
water. It serves, therefore, for their detection and separation. 
It also produces a precipitate in very highly concentrated solu- 
tions of lime, but, in most cases, only after the lapse of some 
time. It does not precipitate dilute solution of lime. The action 
of sulphate of potash being analogous to that of dilute sulphuric 
acid, it is in many cases preferable to the latter reagent, since it 
does not disturb the neutrality of the solution. 

§ 38. 

2. PHOSPHATE OF SODA. (2 N« O, P0 3 .) 

Preparation . — To obtain this reagent pure, dilute commercial 
phosphoric acid is heated, and solution of carbonate of soda 
added, till all effervescence ceases, and the liquid manifests a 
feeble alkaline reaction. The liquid is then filtered, evaporated, 
and crystallized. The crystals are dried, triturated with a portion 
of charcoal and flour, and the entire mass strongly heated in a 
hessian crucible. The heated mass is then boiled with w r ater, 
filtered, and crystallized. One part of the salt obtained is dis- 
solved in ten parts of water, for use. This solution must not 
become turbid on being heated with ammonia. The precipitates 
produced by the addition of solution of barytes, and of silver, 
must completely redissolve on the addition of dilute nitric acid. 

Uses . — Phosphate of soda precipitates the alkaline earths, and 
all metallic oxides, by double affinity. It serves in the course of 
analysis, after the separation of the heavy metallic oxides, as a 
test for alkaline earths in general ; and, after the separation of 
barytes, strontian, and lime, with simultaneous addition of am- 
monia, as a test for the detection of magnesia, which precipitates 
under these circumstances as basic phosphate of ammonia and 
magnesia. 


40 


CYANIDE OF POTASSIUM. 






§ 39. 

3. NEUTRAL CHROMATE OF POTASH. (KO, Cr 0 3 .) 

Preparation . — To obtain this reagent pure, tlie commercial bi- 
chromate of potash is dissolved in water, and carbonate of potash 
added, till the solution manifests a feeble alkaline reaction. The 
liquid, which is now of a yellow colour, is then crystallized. The 
crystals are well washed and re- dissolved in water, in the propor- 
tion of one part of the crystals to ten parts of water. The solu- 
tion must be neutral. 

Uses . — Chromate of potash decomposes, by double affinity, 
most of the soluble metallic salts. The precipitated metallic 
chromates are, for the most part, very difficult of solution, and 
often manifest such peculiar colourings, that the metals they 
contain may be easily detected. Wo use chromate of potash 
principally as a test for lead. 

§40. 

4. CYANIDE OF POTASSIUM. (KCy.) 

Preparation . — To obtain this reagent pure, commercial ferrocy- 
anate of potash is gently heated and stirred, till its water of crystalli- 
zation is completely expelled ; it is then pounded, and eight parts 
of the dry powder are mixed with three parts of perfectly dry car- 
bonate of potash. This mixture is put into a crucible heated to 
redness, and the latter well closed and kept at a bright red heat, 
till the mass is in a state of clear and calm fusion. The fused 
cyanide of potassium is then poured into a heated porcelain 
basin ; this must be doue cautiously, in order to prevent the 
passing over of any particles of the iron which, in a highly- 
divided state, has separated from the mass, and subsided to the 
bottom of the crucible. The thus obtained cyanide of potassium 
is exceedingly well adapted for application in analysis, although 
it contains cyanate of potash. It must be perfectly white. One 
part is dissolved in four parts of cold water. 


FE RROC VAN IDE OF POTASSIUM. 


47 


Uses . — Cyanide of potassium (containing cyanate of potasli) 
produces in the solutions of most metallic salts in water, insoluble 
precipitates of cyanides, oxides, or carbonates. The former of 
these precipitates are soluble in cyanide of potassium ; they may, 
therefore, by a further addition of the reagent, be separated from 
the oxides, &c., which are insoluble in cyanide of potassium. 
Some of the cyanides of metals always dissolve as cyanides com- 
bined with cyanide of potassium, even if free prussic acid be pre- 
sent ; others combine with cyanogen, forming new radicals, and 
as such, combined with potassium, remain in solution. Cobalti- 
cyanido of potassium, ferro and ferri-cyanide of potassium, ore 
the most common combinations of the latter kind. They 
differ from the double cyanogen compounds of the former de- 
scription, especially inasmuch as dilute acids do not separate 
from them the cyanides of metals. Those metals forming such 
combinations may, therefore, by cyanide of potassium, be sepa- 
rated from all those metals, the cyanides of which are precipitated 
by acids, from their solutions in cyanide of potassium. This 
reagent has a highly important special application, in analysis, for 
the separation of nickel from cobalt. 

\ - Ml. 

5. FERROCYANIDE OF POTASSIUM. (C„ N 3 Fc + 2 K=Cfy+2 K.) 

Preparation . — Commercial ferrocyanide of potassium is suffi- 
ciently pure for the purposes of chemical analysis. One part is 
dissolved in twelve parts of water, for use. 

Uses . — Ferrocyanide forms with most metals combinations in- 
soluble in water, and often very peculiarly coloured. These com- 
binations occur when ferrocyanide of potassium is brought into 
contact with soluble salts of metallic oxides, with chlorides, 
&c., the potassium changing places with the metals. Ferro- 
cyanide of copper, and ferrocyanide of iron, show the most cha- 
racteristic colourings of all ; and ferrocyanide of potassium is, 
therefore, especially applied as a reagent for the detection of oxide 
of copper and peroxide of iron. 


48 


HYDROFLUO SILICIC ACID. 


§42. 

6. FERRICYANIDE OF POTASSIUM. 

(C 12 N g Fe + 3 K=2 Cfy + 3 K.) 


Preparation . — Tliis reagent is obtained by transmitting chlo- 
rine gas through a solution of one part of ferrocyanide of potas- 
sium in ten parts of water, till a portion of the fluid, when added 
to a solution of perchloride of iron, no longer produces a blue pre- 
cipitate. or even a blue tinge. The solution is then concentrated 
by evaporation, and some carbonate of potash added, until a 
feeble alkaline reaction becomes manifest. The liquid is then 
filtered, and allowed to cool. The crystals obtained are of a 
magnificent red colour. One part is dissolved in ten parts of 
water, for use. The solution, as already remarked, must neither 
produce a blue precipitate nor a blue tinge, when added to solu- 
tion of perchloride of iron. 

Uses . — Ferricyanide of potassium decomposes with solutions of 
metallic oxides, in the same manner as ferrocyanide of potassium. 
Of all ferricyanides of metals, ferricyanide of iron is peculiarly 
characterized by its colour, and we apply, therefore, ferricyanide 
of potassium especially as a reagent for protoxide of iron. And 
for this purpose it may very well be prepared extempore, by gra- 
dually adding nitric acid to a solution of ferrocyanide of potas- 
sium, till a portion of the mixture no longer imparts a blue 
colour to a solution of chloride of iron. All elevation of tempe- 
rature must be avoided in this process, and the vessel ought to be 
agitated whilst the nitric acid is added. 














§ 43. 

7. HYDROFLUO SILICIC ACID. (3 HF + 2 Si F 3 . ) 

Preparation . — This reagent is obtained in the following man- 
ner : equal parts of fluor spar and sand, in powder, are mixed in 
a glass retort, with six parts of English sulphuric acid; the 
opening of the retort is closed with a perforated cork, into which 


HYDROFLUO SILICIC ACID. 


4!) 


:>ne end of a double-limbed tube is fitted air-tight. The exit 
iml) must reach to the bottom of a flat-bottomed glass jar, and 
:ts extremity be covered with a column of mercury, to the extent 
tf a few lines ; this glass-jar receiver contains four parts of water. 
I disengagement of the fluo- silicic gas immediately takes place, 
ven without the application of beat ; a gentle heat by the sand- 
ath is, however, required to aid the operation. Every bubble 
f gas, as it ascends through the mercury, produces a precipitate 
ff hydrate of silicic acid. One equivalent of ever)' three equi- 
alents of the fluoride of silicon is decomposed in this process, 
nd combines with three equivalents of water, forming silicic acid, 
,’hich precipitates, and hydrofluoric acid, which combines with 
he two remaining equivalents of the fluoride of silicon, forming 
ydrofluo silicic acid. The precipitated hydrate of silicic acid 
enders the liquid gelatinous, and it is on this account that the 
perture of the exit tube must be placed under mercury, for it 
ould speedily be choked if this precaution were neglected. It 
Dmetimes happens in the course, and especially towards the end, 
f the operation, that the gas forms complete tubes or channels 
f silica in the gelatinous liquid, through which it gains the 
ace without decomposition, if they are not broken from time 
> time by stirring. When the disengagement of gas has ceased, 
le gelatinous mass is poured on a piece of linen, and the fluid 
pieezed through. The liquid obtained is then filtered, and kept 
>r use, The hydrofluo-silieic acid, mixed with two parts 

water, produces no precipitate in the solution of salts of 
rontian. 

Uses . — Bases decompose with hydrofluo-silicie acid, form - 
.g water, and metallic fluo-silicates. Many of these com- 
> nations are soluble, others insoluble; the latter may, there- 
■re, by means of this reagent, be distinguished from the former. 
!i the course of analysis, it is only applied for the detection 
’ barytes. 


50 


OXALIC ACID. OXALATE OF AMMONIA. 


§ 44. 

8 . OXALIC ACID. (2 C0 + 0=C 2 0 3 =(J.) 

Preparation . — This ftcid is prepared by pouring upon one part 
of starch, contained in a porcelain basin, five parts of nitric acid, 
of 1 .42, diluted with two parts of water, and applying a gentle 
heat, till no more nitrous gas is evolved. The liquid is then 
filtered and crystallized ; the crystals obtained are drained and 
purified by a second crystallization. Oxalic acid must be pre- 
served in the form of a powder, as it soon decomposes in solution. 
Pure oxalic acid, when boiled with a small quantity of solution 
of indigo, does not discolour the latter. 

Uses . — Oxalic acid combines with many bases, forming salts 
insoluble in water; it may, therefore, bo used to precipitate these 
bases. Many of the oxalates insoluble in water, are easily 
dissolved by an excess of oxalic acid, whilst others dissolve 
with difficulty in the same menstruum. This relation affords 
us, therefore, a means of distinguishing the precipitated 
bases from each other. As all oxalates insoluble in water 
are soluble in stronger acids, (hydrochloric acid, nitric acid,) a 
complete precipitation by oxalic acid ensues, in most cases, only 
when the liberated acid is saturated by an alkali. In analysis, 
oxalic acid is of great importance for the detection and precipita- 
tion of lime. 


§ 45. 

9. OXALATE OF AMMONIA. (NH 4 +O, O.) 

Preparation . — This reagent is prepared by dissolving oxalic 
acid in water, adding ammonia till a feeble alkaline reaction takes 
place, and crystallising. One port of the salt is dissolved in 
twenty-four parts of water, for use. 

Uses . — Oxalate of ammonia is conveniently employed instead | 
of oxalic acid and ammonia. It possesses this advantage over K 
the free acid, that its solution does not decompose on keeping. 




ACETATE OF BARYTES. 


51 


§ 40 - 

10. TARTARIC ACID (C„ H 4 O 10 =T.) 

The tartaric acid of commerce is sufficiently pure for the pur- 
i poses of analysis.* It is best preserved in powder, since it decom- 
ooses with the formation of a white film when kept in solution for 
*•>50106 time. 

Uses . — The addition of tartaric acid to solutions of iron, man- 
ganese, chromium, alumina, cobalt, and many other metals, 
orevents their precipitation by alkalies, by the formation of 
double tartrates indecomposible by alkalies. Tartaric acid may, 
therefore, be employed to separate these metals from others, the 
irecipitation of which it does not prevent. Tartaric acid forms 
vitli potash, but not with soda, a bi-salt difficult of solution; 

: t is, therefore, one of tho best means of distinguishing potash 
tom soda. 

§ 47. 

11. BITARTRATE OF POTASH. (KO, HO, f.) 

The cream of tartar of commerce is sufficiently pure for the 
urposes of qualitative analysis. It should be preserved in powder. 

Uses . — Many metals dissolve in hot solution of tartar, forming 
ouble tartrates; others do not. The former may, therefore, 
•y means of this reagent, be separated from the latter. In ana- 
lysis, tartar is employed in certain cases to separate oxide of 
ntimony from oxide of tin. 

§ 48. 

12. ACETATE OF BARYTES. (Ba 0, A.) 

Preparation . — This reagent is obtained in the same manner as 
trato of barytes, (vide § 33,) substituting, of course, acetic 

* In cases where commercial salts are mentioned, well-defined crystals 
lould be selected. — E d. 

E 2 


CAUSTIC BARYTES. 


f>2 

acid for tho nitric acid. It may conveniently bo preserved in a 
dry state, as it is but of rare application. 

Uses . — The acetate of barytes is employed to convert sulphates 
into acetates, (especially sulphate of magnesia, and the alkaline 
sulphates). As these acetates arc converted by heat into carbon- 
ates, and as carbonate of magnesia is insoluble, whilst the alka- 
line carbonates are soluble in water, acetate of barytes indirectly 
serves to separate magnesia from tho alkalies. 

§ 49. 

13. CAUSTIC BARYTES. (Ba O.) 

Preparation . — To prepare this reagent, one part of sulphuret of 
barium is boiled with twenty parts of water; copper scales are 
then added in excess to tho solution, whilst boiling, till a filtered 
portion of the liquid ceases to blacken a solution of acetate of 
lead. The solution is then filtered, while still hot, and as much 
water added as will prevent any considerable portion of the 
hydrate of barytes in solution from crystallizing on cooling. The 
saturated water of barytes obtained is kept in well-closed bottles. 
Should it contain a small quantity of copper, some sulphuretted 
hydrogen must be cautiously added, and the liquid filtered from 
the precipitated sulphuret of copper. 

Uses . — Caustic barytes is analogous in its action to potash, i. e. 
it precipitates, as a strong base, from saline solutions, those 
metallic oxides and earths which are insoluble in water. In 
analysis, we apply this reagent only for the precipitation of mag- 
nesia. For this purpose a solution of sulphuret of barium may 
equally well be employed, inasmuch as (as is generally the case) 
it contains caustic barytes. Water of barytes may also, like the 
various salts of barytes, of which we have already treated, be 
used to precipitate those acids which form insoluble combinations 
with barytes ; we generally employ it thus only for the detection 
of carbonic acid. 


PROTOCHLORIDE OF TIN. CHLORIDE OF GOLD. 


53 


§ 50. 

14. PROTOCHLORIDE OF TIN. (Sll Cl.) 

Preparation . — To obtain this reagent, English tin is reduced 
to powder, by being fused in an iron spoon, then taken from the 
fire and rubbed in a mortar till it lias reassumed the solid state. 
This powder is then, for some length of time, boiled with con- 
centrated hydrochloric acid in a glass vessel ; (care must always be 
taken that the mixture contains tin in excess ;) the solution is 
diluted with four times its quantity of water, slightly acidulated 
with hydrochloric acid, and filtered. The clear solution is kept 
in a small closed bottle, containing small pieces of metallic tin. 
[f this latter precaution be neglected, the reagent soon becomes 
useless, the protochloride being converted into perchloride of tin. 

Tenting . — Pure protochloride of tin, when mixed with perchlo- 
ride of- mercury, immediately produces a white precipitate of pro- 
tochloride of mercury ; it yields a dark brown precipitate with 
sulphuretted hydrogen, and is neither precipitated nor disturbed 
by sulphuric acid. 

lines . — The great tendency which protochloride of tin has to ab- 
sorb oxygen, and thus to form peroxide of tin, or rather perchlo- 
: ride of tin, as the oxide at the moment of its formation, unites 
' with the free hydrochloric acid present, renders it one of the most 
I powerful means of reduction. We employ it, in analysis, for the 
detection of gold, for which purpose it must first be mixed with 
■some nitric acid, without the application of heat; we also use it 
to detect the presence of mercury. 

§ 51. 

15. CHLORIDE OF GOLD. (AuC1 3 .) 

Preparation . — To obtain this reagent, fine shreds of gold, 
\which may be alloyed either with silver or with copper, are 

I drenched, in a small retort, with aqua regia in excess, and a 
fgentle heat is applied till no more gold is dissolved. If the gold 


51 


CHLORIDE OF PLATINUM. 


was alloyed with copper, which is detected by the brown red pre- 
cipitate produced by ferrocyanide of potassium, in a portion of 
the solution diluted with water, the gold solution containing 
copper is mixed with sulphate of iron in excess. The gold be- 
comes reduced, and separates as a fine brownish black powder ; 
it is then washed in a small retort, re-dissolved in aqua regia, the 
solution evaporated to dryness in the water-bath, and the residue 
dissolved in thirty parts of water. If the gold is alloyed with 
silver, the latter metal remains undissolved as chloride of silver 
when treated with aqua regia. In this case, the first solution is 
evaporated to dryness, and the residue dissolved for use. 

Uses . — Chloride of gold has a great tendency to yield its chlorine 
to other substances ; it therefore easily converts protochlorides 
into perehlorides, protoxides into peroxides and perchlorides, &c. 
These oxidations usually manifest themselves by the precipitation 
of pure metallic gold, in the shape of a blackish brown powder. In 
analysis, chloride of gold serves only for the detection of protoxide 
of tin, as it produces a purple colour or precipitate in solutions 
containing this substance. (Vide infra.). 


§ 52. 

16. CHLORIDE OF PLATINUM. (PtCl 2 .) 

Preparation . — To obtain this reagent, platinum in powder is 
boiled with nitric acid, for the purpose of purification, and then, 
in a retort with narrow neck, drenched with concentrated hydro- 
chloric acid, and some nitric acid ; a gentle heat is applied, and 
from time to time some nitric acid added, until all the platinum 
is dissolved. The solution is, with the addition of hydrochloric 
acid, evaporated to dryness by a water-bath, and the residue 
dissolved in ten parts of water. 

Uses . — Chloride of platinum forms very sparingly soluble double 
salts, with chloride of potassium and hydrochlorate of ammonia, 
whilst it enters into no such combinations with chloride of sodium. 
It serves, therefore, to detect ammonia and potash, and is indeed, 


ZINC. IRON. COPPER. 


for the latter substance, nearly the most susceptible reagent we 
possess. 

§ 53. 

17. zinc. (Zn.) 

Pure, sublimed zinc is selected for the purposes of chemical 
analysis ; it must especially be free from arsenic. The method 
described in § 24 may be employed as a test to detect the pre- 
sence of any trace of this latter substance. The pure zinc should 
be fused, and a portion of it gradually dropped into a large 
vessel, containing water; the remainder should be poured into 
wooden moulds, coated with chalk, for the purpose of casting it 
] ! into little cylinders. 

Uses . — Zinc precipitates many metals in their metallic state, by 
depriving them of their oxygen and acid, owing to the great 
affinity it possesses for oxygen, and its oxide for acids. As tho 
precipitated metals vary in colour, form, &c., zinc may serve as 
well for their detection and distinction from each other, as for 
i their precipitation. We employ it especially for the precipitation 

• of antimony and of tin. Zinc is also frequently used for the pro- 

• duction of hydrogen. 


§ 54. 

18. iron. (Fe.) 

Iron, like zinc, reduces many metals, and precipitates them in 
a pure state. We employ it especially for the detection of cop- 
iper, which is precipitated on it with its characteristic colour. All 
i clean surfaces of iron, such as knife-blades, needles, pieces of 
wire, &c., are well adapted to this purpose. 

§ 55. 

19. copper. (Cu.) 

We employ copper exclusively for the reduction of mercury, 


ACETATE OF POTASH. CAUSTIC LIME 


r,n 


which precipitates thereon as a white coating, which shines witli 
silvery lustre when rubbed. Any copper coin scoured with fine 
sand, in fact any clean copper surface, may bo employed for this 
purpose. 

b. Special reagents which are particularly employed for the de- 
tection and separation of acids, 

§ 56, 

1. ACETATE OF POTASH. (KO, A.) 

Preparation . — This reagent is obtained by dissolving one part 
of pure carbonate of potash in two parts of water, heating the 
solution and exactly saturating with acetic acid. 

Uses . — Every salt of potash may serve to produce a precipitate 
of tartar, and therefore to detect tartaric acid. But the acetate 
of potash is peculiarly adapted for this purpose, as the precipi- 
tated tartar is insoluble in the liberated acetic acid. As this test 
is rarely employed, it is best to prepare it when needed. 

§ 57, 

2. CAUSTIC LIME. (Ca 0.) 

Newly prepared hydrate of lime is agitated and digested for 
somo time in cold distilled water, allowed to settle, and the clear 
fluid decanted and kept in well-closed bottles. Lime-water must 
impart a bright green tinge to Georgina paper, and yield with 
carbonate of potash no inconsiderable precipitate. It becomes use- 
less as soon as it no longer manifests these properties,’ ‘which soon 
takes place, when it is exposed to the access of air. Beside lime- 
water, hydrate of lime also ought to be kept at hand. 

Uses . — Lime forms with some acids insoluble, with others, 
soluble salts. Lime-water may therefore be employed to distin- 
guish those acids from each other, as it precipitates the former 
whilst it yields no precipitate with the latter. Many of the pre- 
cipitable acids are precipitated only under certain conditions, as 


SULPHATE OF LIME. CHLORIDE OF MAGNESIUM. 


5 7 


e. g. on boiling, (citric acid;) and it is therefore easy to distin- 
guish them from each other by altering these conditions. We 
employ lime-water especially for the detection of carbonic acid, 
and to distinguish from each other poratartaric acid, tartaric acid, 
and citric acid. Hydrate of lime serves, like caustic potash, 
to liberate ammonia, and is in many cases preferable to the latter 
reagent. 

| § 58. 

3. SULPHATE OF LIME. (Ca 0, S0 3 .) 

Preparation . — To obtain this reagent, a concentrated solu - 
i tiou of chloride of calcium is mixed with dilute sulphuric acid ; 
i the precipitate produced is well washed, digested, and for some 
' time agitated with water, then allowed to settle, and the clear 
fluid decanted and kept for use. 

Uses . — Sulphate of lime serves for the further subdivision of 
those acids which are precipitable by chloride of calcium, as, 
owing to its difficult solubility, a few acids only of that group 
(oxalic acid, paratartaric acid,) cause precipitates in its so- 
lution. The solution of sulphate of lime serves moreover as 
a reagent for bases, viz., to distinguish barytes, strontian, and 
lime from each other. For, of course, it cannot precipitate the 
latter, whilst it behaves with solutions of barytes and of strontian, 
in the same manner as highly dilute sulphuric acid, i. e. it pre- 
j i cipitates barytes immediately, and strontian only after the lapse of 
! some time. 

§ 59. 

4. CHLORIDE OF MAGNESIUM. (Mg Cl.) 

Preparation . — Chloride of magnesium is prepared by heating a 
; mixture of one pint of hydrochloric acid and two and a half parts 
i of water, and adding basic carbonate of magnesia, (magnesia; 

! carbonas of the shops,) till the liquid ceases to manifest any 
acid reaction. The solution is once more boiled up, filtered, and 


58 


PHOTO-SULPHATE OF IRON. 


kept for use. Sulphate of magnesia may, in most cases, be sub- 
stituted for chloride of magnesium. 

Uses . — Chloride of magnesium almost exclusively serves for the 
detection of phosphoric acid, as it precipitates from the aqueous 
solutions of phosphates, with presence of ammonia, a double salt, 
(basic phosphate of magnesia and ammonia,) which is almost in- 
soluble and highly characteristic in its properties. Chloride of 
magnesium is moreover employed as a test of the purity of hydro- 
sulphuret of ammonia. (Vide § 20.) 

§ 00 . 

5. Proto-sulphate of iron. (Fe O, S0 3 .) 

Preparation . — To obtain this reagent, a quantity of iron nails, 
(free from rust,) in excess, is heated with dilute sulphuric acid 
till no more hydrogen is evolved ; the solution is then filtered, and 
after the addition of a few drops of dilute sulphuric acid, left to 
cool. Crystals are immediately obtained, if the solution was 
sufficiently concentrated, but if more dilute, evaporation must be 
had recourse to. The crystals are washed with water slightly 
acidulated with sulphuric acid, dried and preserved. 

Uses. — Proto-sulphate of iron lias a great disposition to change 
to persulphate of iron, i. e. to absorb oxygen. It acts therefore 
ns a powerful means of reduction. We employ it especially for 
the reduction of nitric acid, from which it separates nitric oxide, 
by depriving it of three atoms of oxygen. As this decomposition 
is attended with the formation of a characteristic, intensely brown- 
ish-black coloured combination of nitric oxide with undecom- 
posed protosulphate of iron, this reaction is particularly charac- 
teristic and susceptible for the detection of nitric acid. Proto- 
sulpliate of iron serves moreover for the detection of ferricyanide 
of hydrogen, with which it produces a kind of Prussian blue, and 
for the detection of gold, wliicli it precipitates from its solutions in 
its metallic state. 


NEUTRAL ACETATE OF LEAD 


59 


§ 61. 

6. SOLUTION OF MAGNETIC OXIDE OF IRON (FERROSO-FERRIC OXIDE.) 

(Fe 0, Fe 2 0 3 .) 

This reagent is not kept on hand, but prepared, when needed, 
by mixing solution of protosulphate of iron with some percliloride 
of iron. (Fe 0, SOa + Fe 2 C1 3 .) It serves for the detection of 
hydrocyanic acid, which when previously combined with alkalies, 
yields with it a precipitate of sesquiferrocyanide of iron (Prussian 
blue) . 

§ 62. 

7. OXIDE OF LEAD. (Pb 0.) 

Oxido of lead is employed for the detection of free acetic acid, 
as it forms with no other acid than this, a soluble combination 
with an alkaline reaction. Finely-washed litharge answers this 
purpose sufficiently well. (Compare § 101, a.) 

§ 63. 

8. NEUTRAL ACETATE OF LEAD. (Pb O, A.) 

The better sorts of commercial acetate of lead are sufficiently 
pure for the purposes of chemical analysis. One part is dissolved 
in ten parts of water for use. 

Uses . — Oxide of lead forms, with a great many acids, combina- 
tions which are insoluble in water, and are distinguished by 
their colour or by some characteristic property. The acetate of 
lead produces, therefore, precipitates in solutions of these acids or 
their salts, and essentially contributes to ascertain and characterize 
several of them. Thus, in particular, chromate of lead is distin- 
guished by its yellow colour, phosphate of lead by its peculiar re- 
lation before the blow-pipe, and niulatc of lead by its easy 
fusibility. 


o 


60 


HYDRATED OXIDE OF BISMUTH. 


§ 64. 

BASIC ACETATE OF LEAD. (3PbO, A.) 

Preparation . — This reagent is obtained by drenching in a well- 
stopped bottle, seven parts of finely-washed litharge, and six parts 
of neutral acetate of lead, with thirty parts of water, and allowing 
them to stand at a moderate heat, shaking it from time to time, 
till the sediment in it has become perfectly white. The clear 
fluid is then decanted and preserved in a well-stopped bottle. This 
acetate of lead is unfit for use, if it contains copper, which is de- 
tected by the blue colour it exhibits on the addition of ammonia. 
It must, in this case, be purified by digesting it with metallic lead, 
till all the copper is precipitated. 

Uses . — The basic acetate of lead, like the neutral acetate, pre- 
cipitates those acids which form insoluble combinations with oxide 
of lead, and indeed all those soluble in acetic acid, more com- 
pletely than the former reagent. Wo employ it in analysis espe- 
cially for the detection of sulphuretted hydrogen, for which sub- 
stance it is nearly the most susceptible reagent. It serves, more- 
over, to neutralize free acids, in cases where it is desirable to avoid 
the application of an alkali, e. g. to render solutions of highly acid 
nitrate of bismuth precipitable by w r ater. 

§ 05. 

HYDRATED OXIDE OF BISMUTH. (Bi 0 + HO.) 

Preparation . — Bismuth reduced to a gross powder is projected 
into pure nitric acid, 1, 2 as long as solution takes place ; this pro- 
cess may be promoted by the application of a gentle heat. The 
solution obtained is diluted with about an equal quantity of warm 
water, (slightly acidified with nitric acid,) and then filtered ; the 
filtrate is mixed with from ten to twenty parts of water, and am- 
monia added to the milky fluid, till the reaction becomes percep- 
tibly alkaline ; the solution is then heated, and the precipitate ob- 
tained washed, first, by decanting the supematunt liquid, and then 


SULPHATE OF COPPER. 


01 


rinsing the precipitate upon a filter, and afterwards drying it be 
:tween some sheets of blotting-paper, at a moderate heat. 

Uses. — The oxide of bismuth, when boiled with alkaline solu- 
tions of sulphurets, decomposes with the latter, giving rise to the 
information of metallic oxides, (corresponding with the various de- 
i.grees of sulphuration of the sulphurets,) and of sulphuret of bis- 
jimuth. It affords us, therefore, especially, a very proper and effi- 
i cicnt means, to convert the sulphuret or bisulphuret of arsenic into 
it arsenious or arsenic acid. 

§ 06 . 

SULPHATE OF COPPER. (Cll 0 , SO3.) 

Preparation . — The blue vitriol of commerce may be purified by 
repeated recrystallization. 

Uses . — Sulphate of copper is employed in qualitative analysis, 
I for the precipitation of hydriodic acid as protiodide of copper. For 
1 this purpose a solution of one part of the blue vitriol must be 
1 mixed with two and a quarter parts of protosulphate of iron, or 
1 else half of the iodine will separate in a free state. The protoxide 
* of iron in this process changes to peroxide, by reducing the per- 
1 oxide of copper to protoxide. Sulphate of copper is besides used 
1 as a test for the detection of arsenious and arsenic acid, and it is 
i indeed as such very susceptible, but by no means characteristic. 
For this purpose it is best to prepare ammonio-sulphate of copper 
I by adding ammonia to a solution of sulphate of copper till the pre- 
1 cipitate which appears at first, is redissolved. We refer to § 94 , 
| d. 0 , for the manner in which sulphate of copper is employed, in 
| junction with caustic potash, to detect arsenious acid, and especially 
to distinguish it from arsenic acid. Sulphate of copper may, more- 
over, be employed for the detection of ferrocyanide of hydrogen. 










peroxide of mercury. 


02 


§ 07. 

12. TROTONITRATE OF MERCURY. (IIg2 0, N0 5 .) 

Preparation. — To prepare this reagent, nine parts of nitric 
acid, of 1.23, arc gently lieated in a small retort, with ten parts of 
mercury, till no more red vapour of nitrous acid appear ; the solu- 
tion is then boiled for some time with the undissolved metallic 
mercury, taking care to replace the water lost by evaporation, till 
a solution of common salt in excess precipitates from a portion of 
the liquid, all the mercury it contains, as a protochloride, so that 
protochloride of zinc produces no precipitate in the filtered liquid. 
The original solution is then shaken until cold ; the crystals ob- 
tained are pounded, and agitated with twenty parts of cold water, 
to which a very small quantity of nitric acid is added. The 
solution is then filtered, if necessary, and kept in a glass bottle, 
the bottom of which is covered with mercury. 

Uses . — The protonitrate of mercury acts in a manner analogous 
to the corresponding salt of silver. In the first place, it preci- 
pitates many acids, especially the hydracids ; and 2, it serves for 
the detection of several substances of easy oxidation, e. g. of formic 
acid, since their oxidation at the expense of the oxygen of the 
black oxide of mercury, is attended by the highly characteristic 
precipitation of metallic mercury. 

§ 08. 

13. PEROXIDE OF MERCURY. (Hg 0.) 

The peroxide of mercury of commerce is reduced to a fine 
powder, after having been moistened with some alcohol, in order to 
prevent its minute particles from rising into the air. This powder 
is then kept for use. As a reagent it affords us a certain means 
of detecting hydrocyanic acid, since it dissolves in an alkaline fluid 
only when this acid is present. (Compare § 100, d.) 


SULPHUROUS ACID. 


63 


§ 09. 

14. PERCHLORIDE OF MERCURY. (Hg Cl.) 

The commercial perchloride of mercury is sufficiently pure for 
: the purposes of chemical analysis. For use, one part is dissolved 
j i in sixteen parts of water. 

Uses. — Prechloride of mercury yields with various acids, e. g. with 
i hydriodic acid, precipitates of a characteristic colour, hut it is, 

I i nevertheless, one of the less essential reagents for the determina- 

I I tion of acids. It acts moreover as a means of oxidation, and allows 
j i us to detect the presence of easily oxidizahle bodies, e. g. of pro- 
toxide of tin, by the precipitation of protochloride of mercury. 

j § 70. 

AMMONIO-NITRATE OF SILVER. (Ag 0, N0 5 + 2 NH 3 . ) 

This reagent is not kept on hand, but prepared, when needed 
for use, by cautiously dropping caustic ammonia into a solution 
■ of nitrate of silver, till the precipitate which at first appears is re- 
i dissolved. It serves for the detection of arsenious and arsenic 
acid in solutions which contain a free acid. 

§ 71. 

SULPHUROUS ACID. (S0 2 .) 

Preparation. — To obtain tins acid, small pieces of charcoal are 
heated in a retort with six or eight times their weight of English 
sulphuric acid, and the evolved gas is transmitted through water 
' (which must be kept cool) till no more sulphurous acid is ab- 
i sorbed. The solution obtained must be kept in well-closed 
I ! bottles. 

Uses. — Sulphurous acid has a great disposition to be con- 
verted into sulphuric acid, by the absorption of oxygen. It is, 
i therefore, one of our most powerful means of reduction ; it 
precipitates metallic mercury from its solutions, and converts 


CHLORINE. 

chromic acid into oxide of chromium, in the same manner as proto- 
chloride of tin. We employ sulphurous acid principally for the con- 
version of arsenic acid into arsenious acid, in order to ho enabled 
to precipitate arsenic more rapidly and more completely, by means 
of sulphuretted hydrogen, (vide § 93, e .) Before applying this 
reagent, it is always necessary to ascertain by its odour whether it 
has undergone decomposition. 


§ 72. 

17. CHLORINE. (Cl.) 

Preparation . — One part of pounded peroxide of manganese is 
drenched in a retort, with from four to five parts of com- 
mercial hydrochloric acid ; a gentle heat is then applied to the re- 
tort, and the evolved gas is conducted into a jar containing about 
from thirty to forty parts of water at the lowest possible tempera- 
ture. The chlorino water obtained must be kept in a well-closed 
bottle, and cautiously protected from the influence of light, for if 
this precaution be neglected, it will soon become completely de- 
composed, i. e. converted into dilute hydrochloric acid, with evo- 
lution of oxygen, (owing to the decomposition of the water.) 

Uses . — Chlorine has a greater affinity for metals and for 
hydrogen than iodine and bromine. Chlorine water is therefore 
an efficient means of expelling iodine and bromine from their 
combinations. Free chlorine forms with bromine, chloride of 
bromine, and with iodine, chloride of iodine, and these combina- 
tions present a different relation to that of the uncombined metal- 
loids ; wc must, therefore, in certain cases, e. g. when testing for 
iodine by means of starch, (§ 100) carefully avoid adding chlorine 
water in excess. Chlorine serves, moreover, for the destruction of 
organic substances, by depriving water, which contains these sub- 
stances, of its hydrogen, so that the liberated oxygen is enabled 
to combine with the vegetable elements, and thus to effect their 
decomposition. For this latter purpose it is most advisable to 
evolve chlorine in the fluid, which contains the organic substances, 
by adding hvdrochloric acid to it, heating it to boiling, and then 


SOLUTION OF INDIGO. STARCH-PASTE. 


05 


adding chlorate of potash. In this process, chloride of potassium 
and water are formed, and chlorous acid and chlorine liberated. 


§ 73. 


18. SOLUTION OF INDIGO. 


Preparation . — One part of pounded indigo is heated with 
seven parts of fuming sulphuric acid. The solution obtained is 
diluted for use, with so much water that the fluid just appears still 
i distinctly blue. 

Uses . — Indigo becomes decomposed when boiled with nitric acid, 
giving rise to the formation of oxidation-products of a yellow colour. 
1 It is therefore employed for the detection of nitric acid, either in 
its free and uncombined state or in its salts ; in which latter 
case, however, the nitric acid must first be liberated by means 
of sulphuric acid. 


§ 74. 

19. STARCH-PASTE. 

Common starch is rubbed with cold water, and the mixture then 
heated to the boiling point, being at the same time constantly 
'Stirred. The paste must be uniform, and so thin as almost to 
rrun. 

Uses. — Starch, when brought into contact with free iodine, 
forms, with this latter substance, a peculiar dark-blue combination, 
Ihe colour of which is so intense that it is distinctly perceptible, 
even when the two substances aro brought together, in a 
highly dilute state. Starch-paste is therefore a most excel- 

lent and delicate test for free iodine. It is by far less susceptible 
with regard to bromine, as the fiery yellow colour of bromide of 
starch is far less characterestic and intense than that of iodide of 
starch. 


F 


(Hi 


CARBONATE OF BARYTES. 


B. REAGENTS IN TIIE DRY WAY. 

1. Fluxes and means of decomposition. 

§ 75. 

1 . MIXTURE OF CARBONATE OF SODA AND CARBONATE OF POTASH. 

( Na 0, C0 2 + KO, C0 2 . ) 

Preparation. — Ten parts of dried carbonate of soda are nibbed 
together with thirteen parts of dry carbonate of potash ; the mix- 
ture is kept in a closed vessel. 

Uses. — When silicic acid or silicates are fused with about four 
parts, (and consequently with an excess,) of carbonate of potash 
or soda, a basic alkaline silicate is formed, (carbonic acid escaping 
with effervescence,) which, being a combination soluble in water, 
may be separated from such metallic oxides as it may peradven- 
ture contain, and from which hydrochloric acid always separates j 
silicic acid in its soluble modification. When a fixed alkaline ; 
carbonate is fused together with sulphate of barytes, of strontia, 
or of lime, carbonates of the alkaline earths and sulphate of the 
alkali present are formed, in which combinations the base, as well 
as the acid of the previously insoluble salts, may now be ascer- , 
tained with facility. In order to enable us to render soluble the 
insoluble silicates and sulphates, we use neither carbonate of 
potash nor carbonate of soda, separately, but the above mixture , 
of both, because this mixture requires a far lower degree of heat ! 
for fusion than either of its components, and thus renders it pos- 
sible to conduct the operation over a Berzelius lamp. This should 
always be done in a platinum crucible, when no easily reducible 
metallic oxides are present. 

§ 76. 

2. CARBONATE OF BARYTES. ( Ba 0, C0 2 . ) 

For the preparation of this reagent we refer the reader to § 33. 

Uses. — When silicates are heated with about six times their 3 




NITRATE OF POTASH. 


G7 


weight of carbonate of barytes till they begin to fuse together, the 
silicates decompose with the salt of barytes, in the same manner 
as with alkaline carbonates, i. e. superbasic silicate of barytes is 
formed, which is easily decomposed by hydrochloric acid, the car- 
bonic acid escapes and the oxides separate. It is, however, by far 
more difficult to render silicates completely soluble by this method, 
than by means of alkaline carbonates, and we use carbonate of 
barytes, therefore, only, when we intend to test silicates as to the 
presence of alkalies. The operation with carbonate of barytes is 

conducted in a platinum crucible. 

• 

§ 77. 

3. NITRATE OF POTASH. ( KO, No 5 . ) 

Preparation . — Commercial saltpetre is dissolved to saturation 
in boiling water. The solution is then diluted with a small quan- 
tity of water, filtered hot into a glass beaker, this latter put into cold 
water, and the solution stirred till cold. The crystalline powder 
• obtained is thrown on a filter and washed with cold w T ater till the 
; filtrate is no longer disturbed by nitrate of silver. It is then well 
i dried and kept for use. 

Testing . — A solution of pure nitrate of potash must neither be 
< disturbed by solution of silver, nor by solution of barytes, nor pre- 
cipitated by carbonate of potash. 

Uses . — Saltpetre serves as a very powerful means of oxidation, 
by yielding oxygen to combustible substances when heated with 
i them. We use it principally to convert several metallic sulphurets, 
jit especially the sulphurets of tin, of antimony, and of arsenic, into 
oxides and acids ; and also for the rapid and complete combus- 
ttion of organic bodies. For this latter purpose, however, nitrate of 
lammonia is in most cases preferable : we obtain this by saturating 
nitric acid with carbonate of ammonia. 


08 


CARBONATE OF SODA. 


II. BLOW-PIPE REAGENTS. 

§ 78. 

1. CHARCOAL. (C.) 

Any kind of completely calcined wood-charcoal may he used for 
blow-pipe experiments. The charcoal of pine or linden- wood is 
however preferable to any other sort. Smooth pieces ought to be 
selected, as knotty pieces split and throw off fragments of the 
test specimen when heated. 

Uses . — Charcoal is principally used as a support for the matter 
under examination in blow-pipe experiments, (vide § 12.) The 
following are the properties which render it so valuable in this re- 
spect, First, its infusihility ; 2nd, its low conducting power for 
heat, which admits of a substance being heated more strongly upon 
a charcoal than on any other support ; 3rd, its porosity, by means 
of which it imbibes easily fusible substances, such as borax, soda, 
&c., wldlst infusible bodies remain on its surface ; 4th, its property 
of reducing oxidized bodies, by means of which it co-operates in 
the reduction of oxides by the inner flame of the blow-pipe. Char- 
coal serves, moreover, for the reduction of arsenious acid and of 
arsenic acid, by depriving them of their oxygen, at a red heat. 
Charcoal, for this purpose, is employed either in the shape of 
small splinters, or reduced to powder. Sometimes the simultane- 
ous application of an alkaline carbonate is necessary for the sepa- 
ration of arsenic ; in such cases it is best to use a mixture of soda 
in powder and lamp-black ; this mixture is heated in a covered 
crucible, and kept in a well-stopped bottle. 

§ 79. 

2. CARBONATE OF SODA. (NaO, C0 2 . ) 

Preparation . — One part of crystallized and three parts of dried 
carbonate of soda are intimately mixed together and then put into 
the broken-off neck of a retort, or into a wide glass tube, or some 


CARBONATE 01' SODA. 


09 


vessel of that description ; one aperture is closed by means of a 
perforated cork, the other remains open. To the perforated cork 
a tube is fitted, which is connected with a gas evolution flask, in 
which, when the entire apparatus is ready, carbonic acid is evolved 
from limestone and hydrochloric acid. We obtain in this manner 
bicarbonate of soda. The complete saturation of the carbo- 
nate of soda with carbonic acid is known by the falling of the tem- 
perature of the mixture which had become elevated in the course 
of the operation, and by the immediate extinction of an ignited 
wood- splint, when held before the open aperture of the tube. The 
salt is then thrown on a filter-funnel and washed with cold water, 
till the liquid which runs off, after supersatimition with nitric 
acid, is no longer disturbed by chloride of barium, or by nitrate 
of silver ; the salt is then diied, and heated in a crucible of silver, 
platinum, or porcelain. Carbonate of soda is thus obtained, 
one atom of carbonic acid being expelled. The purity of carbo- 
nate of soda is tested like that of carbonate of potash. Hydro- 
sulphuret of ammonia must not alter its solution. 

Uses . — We employ carbonate of soda, on account of its fusibi- 
lity, to promote the reduction of oxidized substances bv the inner 
flame of the blow-pipe. In fusing it brings the oxides into 
most intimate contact with the charcoal support, and allows the 
flame of the blow-pipe to embrace every part of the specimen. 
But it does not co-operate in this process by its matter, or by de- 
composition. If tire quantity operated upon is very' minute, the 
reduced metal will often be found in the pores of the coal. In 
such cases, the parts surrounding the little hole which contained 
the sample, are taken oft’ with a knife, triturated in a mortar, and 
the coal washed off from the metallic particles, which then become 
' visible, either as powder or as small and flat spangles, according 
i to their various nature. 

In many cases, e. g. in the reduction of peroxide of tin, it is ad- 
vantageous to add some borax to the carbonate of soda, in order 
tto render the mass more easily fusible. In the second place, car- 
lbonate of soda serves as solvent. It is best to use platinum wire 
as the support, when testing whether bodies are soluble in carbonate 


70 


CYANIDE OF POTASSIUM. 


of soda. For this purpose the substance is made into a paste with 
some carbonate of soda and water ; this paste is placed on the 
loop of a platinum wire, and heated. A few only of the bases dis- 
solve in melting carbonate of soda, but acids dissolve with facility 
therein. Silicic acid differs from all other acids, inasmuch as the 
glass which it forms with carbonate of soda, remains clear on 
cooling, if, of course, tho two constituents are present in the right 
proportion to each other. Carbonate of soda is moreover applied 
ns a means of decomposing, and rendering other bodies soluble, 
especially the insoluble sulphates, with which it exchanges acids, 
whilst, at the same time, a reduction of tho new-formed sulphate 
of soda to sulphuret of sodium takes place ; when fused together 
with sulphuret of arsenic, both are decomposed, giving rise 
to tho formation of sulphuret of arsenic and sodium, and of arsc- 
nito or arseniato of soda, and thus converting it into such a form 
as to admit of its being reduced by means of hydrogen. Finally, 
carbonate of soda is the most susceptible reagent in the dry way, 
for tho detection of manganese, since, when fused together in the 
outer flame of the blow-pipe, with a substance containing manga- 
neso, it produces a green, turbid button, owing to the formation 
of manganate of soda. 


§ 80. 

3. CYANIDE OF POTASSIUM. (KCy.) 

For the preparation of this reagent, vide § 40. 

Uses. — Cyanide of potassium is so powerful as a reducing 
agent in the dry way, that it excels in its action almost fill other 
reagents, and, indeed, it separates the radicals not only from 
oxygen combinations, but also from sulphur combinations, giving 
rise, in the first case, to the formation of cyanate of potash, by 
absorbing oxygen, and, in the latter case, to the formation of sul- 
phocyanide of potassium. We may, by means of this reagent, in 
the easiest manner (commonly merely in a porcelain crucible over 
a spirit-lamp) obtain pure metals from their combinations, as e. g. 
antimony from antimonious acid or from sulphuret of antimony, 


CYANIDE OF POTASSIUM. 


71 


iron from peroxide of iron, &c. &c. The separation of these metals 
is much promoted by the easy fusibility of cyanide of potassium. 
In analysis, this reagent is of the highest importance, for the re- 
duction of arsenites and arseniates, especially of some of those 
salts which have the heavy metals for bases, and the reduction of 
which by the usual means of deoxidizing succeeds only with 
difficulty. As cyanide of potassium is not yet universally known 
as a reagent in this respect, I invito particular attention to its 
superior usefulness in the reduction of arsenic. For experiments 
on a larger scale, glass tubes are selected, rounded at their closed 
end. The salt which it is intended to reduce, e. g. arseniate of 
silver, is thrown into a tube of this description, and covered by a 
small piece of cyanide of potassium ; all moisture is first removed 
from the tube by gently heating it from below upwards ; the 
cyanide of potassium is then heated to fusion and allowed to act 
on the test specimen. The deoxidation begins in a brisk man- 
ner, and with ignition ; it is therefore unnecessary to apply much 
external heat, at tins point of the operation. Up to this time, ge- 
nerally, no incrustation of arsenic appears, but if the melting mass 
be now somewhat more strongly heated, the arsenic will, after some 
time, completely sublime, and as the fused mass does not spout, 
if the interior of the tube is perfectly dry and clean, exceedingly 
beautiful mirror-incrustations will be obtained. For the reduction 
oi very small quantities of compounds of arsenic, we use a per- 
fectly dry mixture of equal portions of carbonate of soda and of 
cyanide of potassium, and cover the test specimen with about six 
times its quantity of this mixture ; conducting the operation in a 
small glass tube expanded at one end into a small bulb. From 
sulphurct ol arsenic also we may completely sublime the arsenic, 
by fusing the sulphuret together with cyanide of potassium. Se- 
veral arsenious and arsenic metallic-salts, when fused together with 
cyanide of potassium, are reduced in such a manner as to give rise 
to the formation of fixed arseniuret, (e. g. arseniate of iron.) In 
such cases no mirror incrustations of arsenic are obtained, which 
must be borne in mind. As a blow-pipe reagent, cyanide of po- 
tassium is also highly useful ; its action is indeed extraordinary : 


72 


BIBORATE OE SODA. 


substances like peroxide of tin, sulphuret of tin, &c. &o., which for 
their reduction with carbonate of soda, require rather a strong 
flame, are reduced with the greatest facility when cyanide of 
potassium is used. In blow-pipe experiments we always use a 
mixture of equal parts of carbonate of soda and of cyanide of 
potassium, since the cyanide of potassium alone fuses too easily. 
This mixture, besides its more powerful action, has another ad- 
vantage over carbonate of soda : it is with extreme facility im- 
bibed by the porous charcoal, so that the purest metallic globules 
are obtained. 


§ 81. 

BIBORATE OF SODA. (BORAX.) (Na 0, 2 B, 0 3 .) 

The purity of commercial borax may be tested, by adding to its 
solution, either carbonate of potash, or, after a previous addition of 
nitric acid, solution of nitrate of barytes or solution of nitrate of silver. 
The borax may be considered pure if these reagents cause no altera- 
tion ; but if they either disturb or precipitate its solution, it must 
be purified by recrystallization. The pure crystallized borax is 
exposed to a gentle heat, in a platinum crucible, till it no longer 
swells up ; it is then triturated and kept for use. 

Uses . — Boracic acid shows a great affinity for oxides, when 
brought into contact with them whilst fusing. It combines there- 
fore, in the first place, directly with oxides. 2. It expels weaker 
acids from their salts ; and 3, with the co-operation of the outer 
flame of the blow-pipe, it disposes metals, sulphur combinations, 
and haloid combinations to oxidize, in order to combine with the 
oxides. Tho borates produced, generally fuse readily by them- 
selves, but by far more easily when fused together with borate of 
soda ; the latter salt acts in this operation either as a mere flux, or 
by giving rise to the formation of double salts. In tho biborate 
of soda, we have 1 , free boracic acid ; and 2, borate of soda ; 
and thus both conditions united, by which, as before stated, oxides, 
sulpliurets, metals, &c. arc disposed for solution and fusion ; 
borax is therefore, as a blow-pipe reagent, of the greatest im- 


PHOSPHATE OF SODA AND AMMONIA. 


73 


fportance in analytical chemistry. We generally select platinum 
wire as support in this operation, heating the loop of it to red- 
mess, dipping it into the borax powder, and holding it in the outer 
■flame, whereby a colourless pearl is obtained. This pearl is 
brought into contact with the test specimen, either when still hot, 
or after being moistened, and thus a small quantity of the latter 
; attached to it ; it is then again exposed, first, to the flame of a 
-spirit-lamp, then to that of the blow-pipe, observing the pheno- 
. mena which appear. The following points ought to be examined 
i with especial care: 1. Whether the specimen dissolves trans- 

parent or not, and whether it retains this transparency on cooling, 
or not. 2. Whether this specimen shows a distinct and definite 
colour, which in many cases, e. g. with cobalt, leads to an in- 
stantaneous and certain detection; and 3. Whether the pearls 
- show the same or a different relation in the outer and inner flame, 
i Phenomena of the latter kind depend on the mutation from higher 
degrees of oxidation to lower, or even to the metallic state, and 
are for some substances particularly significant. 

§ 82. 

■5. PHOSPHITE OF SODA AND AMMONIA. (MICROCOSMIC SALT.) 

(Na O, NH 4 0, P0 S .) 

Preparation . — This salt is obtained by dissolving six parts of 
[phosphate of soda and one part of pure sal-ammoniac in two 
•.parts of hot water, and allowing the mixture to cool. The 
crystals of the double salt thus obtained are purified by recrystal- 
lization from the chloride of sodium which still adheres to them. 
They are then dried, powdered, and kept for use. 

Uses . — When phosphate of soda and ammonia is heated, the 
ammonia escapes together with the waiter of crystallization. 
There remains consequently a compound, which, with regard to 
.composition, (free acid and fusible salt,) very nearly approaches 
borax. The action of microcosmic salt is therefore quite analo- 
gous to that of biborate of soda. We prefer it, however, to borax 
in many cases as a solvent or flux, knowing by experience that 


74 


PROTO-NITRATE OE COBALT. 


the glasses which it forms with many substances, are more 
beautifully and distinctly coloured than those of borax. Platinum 
wire is equally used as a support when employing microcosmic 
salt as a flux ; it ought, however, here to be remarked, that the 
loop of the wire must be small and narrow, or else the pearl will not 
stick to it. The operation is conducted as stated § 81 in the pre- 
ceding paragraph. 


§ 83. 

TROTO-NITRATE OF COBALT. (Co O, NO/s.) 

Preparation . — To obtain this reagent, an intimate mixture of 
two parts of very finely pounded cobalt, four parts of saltpetre, 
one part of effloresced carbonate of soda, and one part of dry 
carbonate of potash, is projected in small portions into a crucible 
heated to redness ; the latter is then left exposed to the strongest 
possible heat, till the mass, although perhaps not in perfect fusion, 
yet is melting. The mass is then allowed to cool, and afterwards 
reduced to powder and boiled with water ; the impure peroxide of 
cobalt obtained is completely washed, digested and heated with 
hydrochloric acid until dissolved. This solution is of a dark 
green colour, and generally gelatinous, owing to the separation of 
silicic acid. It is evaporated to dryness, the residue boiled with 
water, filtered, and carbonate of ammonia added to the filtrate, 
whilst kept at the boiling point, till all acid reaction ceases. The 
filtered solution is precipitated by means of carbonate of potash, 
the precipitate obtained washed and then dissolved in nitric acid. 
The solution is evaporated to dryness, at a gentlo heat, and one 
part of the residue dissolved in ten parts of water, for use. 

Uses . — The protoxide of cobalt, when heated with certain infusible 
substances, forms with them combinations of divers various charac- 
teristic colours, and may therefore serve for the detection of thoso 
substances. Experiments of this kind are conducted in the fol- 
lowing manner. The substance under examination, reduced to 
powder, is heated to redness, on a charcoal support, the smallest 
possible drop of solution of proto-nitrate of cobalt is then dropped 




PROTO- NITRATE OF COBALT. 


75 


lupon it, and it is again heated to redness. In this process, 
oxide of zinc assumes an intensely green colour, alumina a blue, 
land magnesia a feeble rose tint. The rose tint of magnesia is of 
-so little intensity that beginners may easily overlook this reaction. 
-Silica also, when moistened with solution of nitrate of cobalt and 
heated to redness, assumes a feeble blue tint, which ought to be 
i borne in mind when testing for alumina. The blue compound of 
ithe latter is, however, by far more beautifully and intensely 
coloured, than that of silica. 


CHAPTER III. 


ON THE RELATION OF THE VARIOUS SUBSTANCES TO 

REAGENTS. 

§ 84 . 

As we have stated in our introductory remarks, qualitative 
analysis is based on experiments by means of which we endeavour to 
convert tire unknown constituents of a substance into forms with the 
relations and properties of which we are familiar, so as to enable us 
to determine the nature of constituents. It is the same with such 
experiments as with inquiries and investigations in general. They 
are the better the more certainly they lead to a definite result, no 
matter whether of a positive or negative character. But as a 
question does not render us a whit the wiser, if we do not under- 
stand the language in which the answer is returned, so an ex- 
periment cannot aviul us if we do not know the manner of ex- 
pression in which the information is conveyed to us, i. e., if we do 
not know what conclusion we are to draw from a reagent leaving 
a body unaltered, or producing some phenomenon or other, owing 
to a mutation of form or state in the substance operated upon. 

Before we can, therefore, proceed to the practice of analysis, we 
must, as an indispensable condition, first really and completely know 
those forms and combinations of substances, which are supposed 
to be known. But this perfect knowledge depends, first, on a com- 
prehensive conception of the conditions which are necessary for 
the formation of the new combinations, and thus, in short, for the 
manifestation of the various reactions ; and 2ndly, on a distinct 
impression of the colour, form, and physical properties in general 
which characterize the new combinations. 

It is, therefore, of paramount importance to the student, not 


POTASH, SODA, AMMONIA. 


77 


■ merely theoretically to study this branch of qualitative analysis, 
llmt also by actual experiments to verify every part of it. To 
t teach the relation of the various bodies to reagents, it is usual, in 
\ works like the present, to treat of the substances individually and 
-separately, and to point out their characteristic reactions. I have, 
i however, in the present work, deemed it more judicious and better 
adapted to its elementary character, to collect into groups those 
-substances which are in many respects analogous, and thus by 
confronting their analogies with their differences, to place the 
latter in the clearest possible light. 

A. — RELATION OF THE METALLIC OXIDES. 

§ 85. 

First Group. 

POTASH, SODA, AMMONIA. 

Properties of the group. — The alkalies are easily soluble in 
water, as whether in their pure — or caustic state — or as sulphurets 
i and carbonates. They, therefore, do not precipitate each other, 
t neither in their pure state nor as carbonates, nor are they preci- 
pitated by sulphuretted hydrogen under any condition whatever. 
The solutions of the pure alkalies, as well as of their sulphurets 
and carbonates, tinge reddened litmus paper blue, and impart an 
intensely brown tint to turmeric paper. 

Special reactions characteristic of the individual substances, 
a. potash. (K O.) 

1 . The salts of potash are not volatile in the heat of a spirit- 
lamp. They almost all dissolve in water with facility. Their 
‘solutions are colourless provided the constituent acid be so. The 
neutral salts of potash with strong acids, do not affect vegetable 
(colours. Carbonate of potash is of difficult crystallization. The 
dry salt as well as the crystals, (KO, COa, 2 aq.) which are 
formed in concentrated aqueous solutions of carbonate of potash, 


78 


POTASH, SODA, AMMONIA 


when allowed to stand for some time, deliquesce with rapidity 
when exposed to humid air. 

2. Chloride of platinum produces in the neutral and acid 
solutions of the salts of potash, a yellow crystalline heavy pre- 
cipitate. (Chloride of platinum and potassium. K Cl-f 
P + Cl 2 . ) In concentrated solutions, the formation of this pre- 
cipitate is immediate, in dilute solutions it takos place after a 
short time, and frequently even after the lapse of some time. 
The presence of free hydrochloric acid promotes its formation. It 
is difficultly soluble in water, and wholly insoluble in alcohol. 
Chloride of platinum is therefore a particularly delicate test for 
salts of potash when the latter is in alcoholic solution. Care 
should be taken to avoid confounding chlorido of platinum and 
potassium with chlorido of platinum and ammonium. 

8. Tartaric acid produces, in neutral or alkaline solutions of 
salts of potash, (to alkaline solutions the reagent must be added 
till a strongly acid reaction becomes manifest,) a white, quickly 
subsiding, granular crystalline precipitate of bi-tartrate of 
potash. (KO, HO, T.) In concentrated solutions this preci- 
pitate is formed immediately, in dilute solutions frequently only 
after the lapse of some time. Violent agitation of the liquid 
considerably promotes the formation of the precipitate. Free 
alkalies and free mineral acids dissolvo the precipitate; it is 
difficultly soluble in cold, but more easily so in hot water. 

4. When salts of potash, by means of a platinum wire, are held 
in the summit of the inner blow-pipe flame, the outer flame assumes 
a violet tint, owing to a reduction of potash, and a reoxidation 
of the potassium thus formed. This reaction is hardly percep- 
tible in phosphates and borates of potash. The presence of soda 
renders it completely imperceptible. 

5. When a salt of potash is heated with a small quantity of 
water, alcohol added, and the latter ignited, the flame appears 
violet. The presence of soda renders this reaction also imper- 
ceptible. 


SODA. 


79 


b. soda. (Nn 0.) 

1. The salts of soda present the same general relations as 
tthose of potash. Carbonate of soda crystallizes readily; the 
crystals (Na 0, C0 2 + 10 nq.) effloresce rapidly when exposed to 
idry air. 

2. If a neutral or alkaline solution of a soda salt be mixed 
with a solution of neutral antimoniate of potash* a white gra- 
mular crystalline precipitate, antimoniate of soda (Na 0, 
8Sb 0 5 ) is formed, (in concentrated solutions, almost immediately, 
;dn dilute solutions after the lapse of some time.) Violent agitation 

of the mixture promotes the separation of the precipitate very 
much ; rubbing the inner sides of the vessel with a glass rod is 
even more effective. Even in solutions of soda, diluted to the 
extent of 1000 to 1, we observe, after the lapse of some time, 
i a certain milkiness, and finally the formation of a crystalline 
i [precipitate. This reaction is not interfered with by the presence 
of salts of potash ; the presence of carbonate of potash, in excess, 
Malone has a preventive influence on the formation of the precipitate, 
:-since antimoniate of soda dissolves more readily in solution of 
ecarbonate of potash, than in water. The presence of free acids 
rmust always be avoided, since they separate from the reagent, 
Ibi-antimoniate of potash, or hydrate of antimonic acid, in the form 
i of a white precipitate. 

3. Salts of soda exposed on a platinum wire to the inner blow- 
i pipe flame, colour the outer flame intensely yellow, owing to 
:ia reduction of soda, and a re-oxidation of the sodium formed. 
This reaction is visible even if a large quantity of potash is mixed 

i with the soda. 

* This reagent is prepared by exposing fifty parts of antimonium diapho- 
rreticum ablutum, mixed with twenty and four tenth parts of pure carbonate 
cof potash, to a red heat for half an hour. The crumbling mass is kept in a 
•■well-stopped glass vessel. The solution is prepared by drenching four parts of 
ithe powder with one hundred parts of warm water, allowing it to digest, and 
' to cool completely, and then filtering the solution and preserving the clear 
filtrate, protected from the access of air. 


(5 


80 


AMMONIA. 


4. \\ lien n salt of soda is heated with a small quantity of water, 
alcohol added, and the latter ignited, the flame appears strongly 
yellow. The presence of a salt of potash has no preventive influ- 
ence on this reaction. 

!). Chloride of platinum produces no precipitate in solutions 
of soda : tartaric acid only when they are highly concentrated. 
The bitartrate of soda, (Na 0, IIO, T + 2 aq.) which crystal- 
lizes out in such cases, appears always in the shape of small 
needles and columns, and not, like the corresponding salt of 
potash, in the form of a granular crystalline precipitate. 


c. ammonia. (NH 4 0.) 

1. All salts of ammonia are volatile at a high temperature, 
either with decomposition, or remaining in combination. Most 
of them are easily soluble in water. Their solutions are colour- 
less. The neutral ammoniacal compounds with strong acids do 
not alter vegetable colours. 

2. When salts of ammonia are triturated with hydrate of lime, 
with the addition of a few drops of water, or when they are 
heated, cither in a solid form or in solution, with solution of 
potash, ammonia becomes liberated in its gaseous state, and 
manifests itself, 1, by its characteristic odour; 2, by its re- 
action on moistened test-papers; and 3, by giving rise to 
the formation of white fumes, when any object (e. g. a glass 
rod) moistened with hydrochloric acid, nitric acid, acetic acid, 
any volatile acids, is brought in contact with it. These 
fumes are caused by the formation of fixed salts, produced by 
the contact of the gases in the air. Hydrochloric acid is the 
most delicate test in this experiment ; acetic acid, however, less 
easily admits of any mistake. 

3. Chloride of platinum shows the same relation to salts of 
ammonia as to salts of potash ; the yellow precipitate of chloride 
of platinum and ammonium (NH 4 C1 + P + C1 2 ) has, however, a 
somewhat lighter colour than chloride of platinum and po- 
tassium. 

c. Tartaric acid produces in solutions of salts of ammonia a 




BARYTES, STRONTIAN, LIME, MAGNESIA. 


81 


I [precipitate of bitartrate of ammonia, (NH 4 0, HO, T,) which 
iis formed in the same manner, and under the same circumstances 
as the corresponding salt of potash, but is somewhat more 
soluble than the latter. 


Recapitulation and, remarks. — Salts of potash and of soda are 
mot volatile at a common red heat; salts of ammonia volatilize 
’easily. The latter may, therefore, be easily separated from the 
('former by the application of a red heat. The surest test of ammonia 
iis its expulsion by lime or potash. Salts of potash can only he 
f detected when salts of ammonia are removed, since both show 
] ithe same or similar relations to chloride of platinum and tartaric 
acid. Potash is characterized with certainty by either of these 
two reagents, when ammonia is removed. Soda can only be 
positively detected by the figure of crystallization, and the properties 
of some of its salts by its behaviour with antimoniate of potash, 
•and by the colour which its salts impart to the flame of the blow- 
pipe, and to that of alcohol. When testing for soda with anti- 
nmoniate of potash, ammoniacal salts must not be present, as they 
-mlso yield precipitates with the same reagent. If the soda is 
combined with potash in alkaline solution, and we intend to test 
for it with antimoniate of potash, acetic acid, or hydrochloric 
tacid, must first be added, until the alkaline reaction has nearly 
but yet not completely disappeared. If the fluid under exami- 
hnation contains a free acid , pure carbonate of potash is added, 
a until tho solution has acquired an incipient alkaline reaction. 


§ 86 . 


Second Group. 

BARYTES, STRONTIAN, LIME, MAGNESIA. 

Properties of the group. — The alkaline earths are soluble in 
r water, in their caustic state and as sulphurets. Magnesia, how- 
ever, is very difficult of solution. These solutions manifest 
nlkaline reactions. The neutral carbonates and phosphates of the 

G 


82 


BARYTES. 


nlkftline earths are insoluble in water. The solutions of the salts 
of the alkaline earths are, therefore, not precipitated by sulphu- 
retted hydrogen, under any condition, but alkaline carbonates 
and phosphates do precipitate them. This relation distinguishes 
the oxides of the second group from those of the first. The 
salts of the alkaline earths are colourless, partly soluble, partly 
insoluble, and not volatile. 


Special Reactions, 
a. barytes. (Ba 0.) 

1. Ammon ia causes no precipitate in the solutions of salts of 
barytes; potash only when they are concentrated. Water re- 
dissolves the precipitate of hydrate of barytes (BaO + aq.) 
which is formed. 

2. Alkaline carbonates throw down from solutions of barytes 
carbonate of barytes, (Ba 0, CO2. ) in the form of a white preci- 
pitate. In acid solutions, however, complete precipitation takes 
place only on boiling ; the same is the case when carbonate of 
ammonia is employed as the precipitant. The presence of salts of 
ammonia does not prevent this precipitation. 

3. Sulphuric acid, and all the soluble sulphates, produce, even 
in the most highly diluted solutions of barytes, immediately, a fine 
white precipitate, sulfhate of barytes, (Ba 0, SO3 ) which is 
insoluble in acids and alkalies. 

4. H;/dr of uo- silicic acid precipitates from solution of barytes 
silicofluoride of barium, (3 Ba F1+ 2 Si FI 3 ’) in the form of a 
colourless, crystalline, quickly-subsiding precipitate. In dilute 
solutions this precipitate is formed only after the lapse of some 
time, hydrochloric acid and nitric acid dissolve it, but only to 
a hardly perceptible extent. 

f,. Phosphate of soda causes in neutral or alkaline solution, a 
white precipitate of phosphate of barytes, (Ba O, P0 5 ) which 
is soluble in free acids. Addition of ammonia neither increases 
the quantity of this precipitate, nor promotes its formation. 

6. Oxalic acid causes only in concentrated solutions a white 






STRONTIAN. LIME. 


83 


precipitate of oxalate of barytes, (Ba 0, O + aq.) which is 
soluble in acids. But if ammonia be added, the reaction is by 
par more susceptible, and the solution must be highly dilute 
■indeed if no precipitate is formed. 

7. Salts of barytes, when heated with diluted spirit of untie, 
mpart to the flame of the latter a but little characteristic yellowish 
i colour. 


b. STRONTIAN. (Sr 0.) 

1. Salts of strontian show completely the same relations as 
[salts of barytes, to ammonia and potash, as well as to the alkaline 

•arbonates, and to phosphate of soda. 

2. Sulphuric acid and sulphates precipitate from solutions of 
trontian, sulphate of strontian, (Sr O, S0 3 ) in form of a 

iVhite powder, which is insoluble in acids and alkalies. Sulphate 
of strontian is by far more soluble in water than sulphate of 
■arytes, owing to which the precipitate in rather dilute solutions 
:>* generally only formed after the lapse of some time ; and this 
a always the case (even in concentrated solutions) if solution of 
gypsum is employed as the precipitant. 

3. Hydrofluo-silicic acid does not cause any precipitate, even 
l concentrated solutions of strontian. 

4. Oxalic acid precipitates even from rather highly dilute 
elutions, after the lapse of some time, oxalate of strontian, 
'Sr 0, O + aq.) as a white powder. Addition of ammonia pro- 
motes the formation of the precipitate, and considerably increases 
ss quantity’. 

5. If such salts of strontian as are soluble in water or alcohol, be 
eated with diluted alcohol, and the latter ignited, they impart to 
'S flame, especially on stirring, an intense carmine red colour. 

■ his colour must not be confounded with that which salts of lime 
i mmmunicate to the flame of alcohol. 


c. lime. (Ca 0.) 

1 . Ammonia, potash, alkaline carbonates, and pthosphate of 


G 2 


MAGNESIA. 


yi 

soda, show the same relations to salts of lime as to salts of 
barytes. 

2. Sulphuric acid and sulphate of soda produce in highly- 
concentrated solutions of lime immediately, white precipitates of 
SULPHATE OF lime, (Ca O, S0 3 , HO + aq.) which are completely 
dissolved by a large proportion of water, hut are far more 
soluble in acids than in water. In less concentrated solutions the 
precipitates are only formed after the lapse of some time ; and 
no precipitation whatever takes place in highly dilute solutions. 
Solution of gypsum, of course, cannot produce any precipitate ; 
but even a cold saturated solution of sulphate of potash, mixed 
with an equal quantity of water, produces no precipitate in solu- 
tions of lime, at least never immediately. If solutions of lirue 
are so highly dilute, that sulphuric acid causes no precipitation 
in them, a precipitate is immediately formed on the addition of 
alcohol. 

3. Hi/drojluo- silicic acid does not precipitate salts of lime. 

4. Oxalic acid produces a white precipitate of oxalate of 
lime, (Ca O, 0 + 2 aq.) even in highly dilute neutral solutions of 
lime. Addition of ammonia promotes the formation of this pre- 
cipitate, and increases its quantity. Oxalate of lime is easily 
soluble in hydrochloric acid and nitric acid, but not in acetic 
acid, nor in oxalic acid. 

Soluble salts of lime, when heated with dilute alcohol, impart 
to the flame of the latter a yellowish red colour, which is often 
confounded with that caused by strontium 

d. magnesia. (Mg O.) 

1. Ammonia throws down from the solutions of neutral salts of 
magnesia, a portion of the magnesia as hydrate of magnesia, 
(Mg O, HO,) in the form of a white bulky precipitate. The 
other portion of magnesia remains in solution, combined with the 
salt of ammonia to which the decomposition has given rise, and 
forming with it a double salt, not decomposible by ammonia. 
This disposition of the salts of magnesia to form such double 
salts with salts of ammonin, is the cause that salts of magnesia are 




MAGNESIA. 


85 


mot precipitated when salts of ammonia are present, or, what is in 
jaact the same, that ammonia does not produce any precipitate in 
Lcid solutions of magnesia, and that a precipitate caused by 
ammonia, in neutral solutions, is re-dissolved on the addition of a 
• >alt of ammonia. 

2. Potash and caustic barytes precipitate from solutions of 
(magnesia, hydrate of magnesia. The formation of this pre- 
cipitate is much promoted by boiling. Salts of ammonia re- 
l.issolve the precipitated hydrate ; and no precipitate is formed at 

; 11, if they are mixed in sufficient quantity with the magnesia 
olution, before the addition of the precipitant. But it will of 
:ourse make its appearance if the solution be then boiled with 
m excess of potash, for in that case the condition of its re- 
naming in solution, i. e. the salt of ammonia, becomes decom- 
iosed and is thus removed. 

3. Carbonate of potash causes in neutral solutions of magnesia a 
rkhite precipitate, a compound of one equivalent of hydrate 
i*F MAGNESIA, AND THREE EQUIVALENTS OF CARBONATE OF MAG- 
iesia. (Mg 0, HO + 3 Mg O, COo. ) The fourth part of the 
iurbonic acid contained in the carbonate of potash becomes 
liberated on the decomposition of this salt, and combining with a 

ortion of the new-formed carbonate of magnesia, keeps this part 
n solution as a bicarbonate of magnesia. Tliis carbonic acid may 
e expelled by boiling ; the application of heat to the solution, 
herefore, promotes the formation and increases the quantity of 
ie precipitate. Salts of ammonia prevent this precipitation also, 
nd re-dissolve a precipitate already formed. 

4. Carbonate of ammonia does not precipitate solutions of 
magnesia when cold, and but imperfectly when boiling. The 
ddition of salts of ammonia completely prevents the formation of 
(precipitate. 

Phosphate of soda precipitates phosphate of magnesia 
•2 Mg 0, PO5 ) as a white powder, from solutions of magnesia, 
rrovided they be not too highly dilute. The precipitation is 
much promoted by boiling the solution. But if ammonia be 
aided to even a highly diluted solution of magnesia, no matter 


80 


MAGNESIA. 


whether before or after the addition of the phosphate of soda, a 
white crystalline precipitate of basic phosphate of magnesia 
and ammonia (2 Mg O, NTH 0,) (P0 8 + 2 HO + 10 aq.) is 
formed. Its separation from dilute solutions is much promoted 
by violent stirring (with a glass rod), if even the solution is 
too highly diluted as to admit of the formation of a precipitate ; 
yet white lines appear after some time in those places of the sides 
of the vessel which have been touched by the glass rod whilst 
stirring the fluid. Muriate of ammonia and salts of ammonia in 
general do not dissolve the basic phosphate of magnesia and am- 
monia, but it is soluble in free acids, (even in acetic acid). 

G. Oxalate of ammonia (but not free oxalic acid) produces a 
white precipitate of oxalate of magnesia. (Mg 0, 6 + 2 aq.) 
Salts of ammonia prevent its formation. 

7. Sulphuric acid and hy dr ojiuo- silicic acid do not precipitate 
salts of magnesia. 

8. If magnesia, or a salt of magnesia, bo moistened with 
solution of protonitrate of cohalt, and for some time exposed on 
a coal to a strong blow-pipe flume, a feebly flesh-colouked 
mass is obtained, the tint of which only becomes distinct on cool- 
ing, but is never very intense. 

Recapitulation and remarks. — The difficult solubility of the 
hydrate of magnesia, the easy solubility of the sulphate of mag- 
nesia, and the disposition of salts of magnesia to form double 
salts with salts of ammonia, are the three main points in which mag- 
nesia differs from the other alkaline earths. To detect magnesia, 
we remove always first barytes, strontian, and lime, if they are 
present ; and we effect this purpose either by boiling with carbo- 
nate of ammonia with addition of sal ammoniac, or by means of 
sulphate of potash and of oxalate of ammonia, with addition of 
sal ammoniac, and then select for the detection of magnesia, the 
reaction with phosphate of soda, with addition of ammonia. The 
detection of barytes is always easy, for the immediately forming 
precipitate which it yields with solution of gypsum, and its reac- 


ALUMINA. 


87 


i on with liydrofluo silicic acid, leave no doubt as to its presence 
:trontian may also easily be detected by its relation to solution of 
vypsum, except in cases where barytes' is present. It must, there- 
brre, in such cases first be separated from barytes. This separa- 
on may best be effected by converting both earths into dry 
llorides, and digesting the latter with absolute alcohol. The 
lloride of strontian dissolves whilst the chloride of barium re- 
gains undissolved. When testing for strontian by means of the 
_oohol flame, we must avoid confounding the colour it imparts to 
, with that communicated by salts of lime. For the detection of 
me, oxalic acid is always selected. Barytes and strontian must, 
owever, first have been removed by means of sulphate of potash, 
ncc they manifest with oxalic acid an analogous reaction, only 
rarying in intensity. On the separation of barytes and strontian, 
y means of sulphate of potash, it may possibly happen that also 
[ portion of the lime precipitates. This is, however, a matter of 
u difference, since, at any rate, sufficient remains dissolved in the 
aid to admit of its presence being ascertained with indubitable 
rrtainty, by means of oxalic acid. 


§ 87 . 

Third Group. 

ALUMINA, OXIDE OF CHROMIUM. 

Properties of the group . — Alumina and oxide of chromium are 
oth in their pure state, and, as hydrates, insoluble in water. They 
rm no neutral salts with carbonic acid. Their sulphur combina- 
ons cannot be formed in the humid way. Sulphuretted hydro- 
?n, therefore, does not precipitate solutions of alumina or oxide 
chromium ; hydrosulphuret of ammonia precipitates the 
^drated oxides from these solutions. This relation to hydrosul- 
mret of ammonia distinguishes the oxides of the third from 
i ose of the two preceding groups. 


88 


OXIDE OE CHROMIUM. 


Special Reactions. 

a . ALUMINA. ( Al 2 Oa ) I 

1. The salts of alumina are colourless, for the most part not 
volatile ; some of them are soluble, others insoluble. The soluble 
salts redden litmus paper and lose their acids, when heated to 
redness. 

2. Potash throws down from the solutions of alumina a bulky 
precipitate of hydrate of alumina, (Al 2 0 3 + HO,) containing 
potash, which easily and completely dissolves in an excess of tlio 
precipitant, hut may again be precipitated from this solution by 
the addition of hydrochlorate of ammonia, even when the solution 
is cold, but more completely on heating it. The presence of salts 
of ammonia does not prevent this precipitation by potash. 

3. Ammonia also produces a precipitate of hydrate of alu- 
mina; and this precipitate also is redissolved by a very consi- 
derable excess of the precipitant, but only in such cases where the 
solution of alumina contains no salts of potash or soda. But if a 
certain quantity of these salts is present, ammonia is not able to 
redissolve the precipitate first formed. 

Upon this relation, the complete precipitation of the hydrate of 
alumina from a potash solution, by means of hydrochlorate of am- 
monia, depends. For in this process, potash and hydrochlorate of 
ammonia mutually decompose, giving rise to the formation of 
chloride of potassium and of ammonia ; and ammonia not being 
able to maintain the hydrate of alumina in solution, when a salt 
of potash is present, this hydrate of course precipitates. 

4. If alumina, or a compound of alumina, be heated to redness, 
on charcoal, before the blow-pipe, and then moistened with a few 
drops of solution of protonitrate of cobalt, and again strongly 
heated, an unfused mass of a deep sky-blue colour is obtained, ft 
compound of the two oxides. The colour becomes distinct only 
on cooling. By candle-light it appears violet. 


OXIDE OF CHROMIUM. 


39 


b. OXIDE OF CHROMIUM. (Cr 2 0 3 .) 

1 . The solutions of the compounds of oxide of chromium, have 
always, even when highly diluted, either an emerald-green or a 
ligrescent violet colour. The soluble neutral salts of oxide of 
•hromium redden litmus paper, and are decomposed by heat. 

2. Potash produces in solutions of oxide of chromium, a bluish- 
;:p-een precipitate of hydrated oxide of chromium (Cr 20 3 + HO) 
( \,vhich easily and completely redissolves in an excess of the preci- 
oitant, imparting an emerald-green colour to the fluid. If this 
solution is kept constantly boiling for a certain time, the preci- 
pitate completely separates again, so that the supernatant liquor 
appears perfectly colourless. The dissolved hydrated oxide of 
chromium is also precipitated, if the potash solution is mixed 
with hydrochlorate of ammonia and heated. 

3. Ammonia produces the same precipitate of hydrated oxide 
df chromium. An excess of the precipitant redissolves it to a 

t-small extent, at a low temperature, but the precipitation is com- 
plete, if the solution is boiled after the addition of ammonia in 
excess. 

4. If oxide of chromium, or a compound of this substance, are 
fused together with nitre, chromate of potash, (KO, Cr0 3> ) is 
obtained in all cases ; in this process a portion of the oxygen of 
itlie nitric acid leaves its combination, and forms with the oxide of 
chromium, chromic acid, which then combines with the potash of 
khe decomposed saltpetre. For the Reaction of Chromic Acid, 
'vide infra, § 95, b. 

5. Phosphate of soda and ammonia dissolves oxide of chro- 
mium and its salts, as well in the oxidizing as in the reducing 
flame of the blow-pipe, giving rise to the formation of clear, 
feebly yellowish-green glass, the colour of which changes to 
emerald-green, on cooling. Borax manifests a similar relation. 

Recapitulation and remarks. — The solubility of the hydrates 
of chromium and alumina, in potash and their precipitation from 




90 


OXIDE OF ZINC. 


potash solutions, by means of hydrochlorate of ammonia allows us, 
in the first place, to separate them from the oxides of other groups, 
and affords us, in the second place, a certain means of detection 
for alumina, when no oxide of chromium is present. If the 
latter, therefore, is present — which we may ascertain either by the 
colour of the solution, or, at any rate, by the reaction with phos- 
phate of soda and ammonia, — it must be separated before we can 
proceed to test for alumina. This separation may bo effected 
most completely by fusing the mixed oxides together with nitre. 
The precipitation of oxide of chromium, by means of boiling its 
potash solution, is also a sufficiently exact indication ; it gives, 
however frequently rise to mistakes. 

§ 88 . 

Fourth Group. 

OXIDE OF ZINC, PROTOXIDE OF MANGANESE, OXIDE OF NICKEL, 
PROTOXIDE OF COBALT, PROTOXIDE OF IRON, PEROXIDE OF 
IRON. 

Properties of tlie group . — The sulphurcts corresponding with 
these oxides, are more or less soluble in dilute acids, but in- 
soluble in water, alkalies, and alkaline sulphurcts. The solutions 
of the salts of these oxides, are therefore not at all precipitated by 
sulphuretted hydrogen, when they contain free acid, and either 
not at all, or at least but incompletely, when they are neutral, but 
completely, when they are alkaline, or when an alkaline sulpliuret 
is employed instead of sulphuretted hydrogen. 

Special Reactions, 
a. oxide of zinc. (ZnO.) 

1 . The compounds of oxide of zinc arc colourless. Its soluble 
neutral salts redden litmus paper, and are easily decomposed by 
heat, with the exception of sulphate of zinc, which can bear a 
slight degree of red heat. 




. PROTOXIDE OP MANGANESE. 


91 


2. Sulphuretted hydrogen precipitates from neutral zinc solu- 
i ions, a portion of the zinc as white sulphuret of zinc (Zn S.) 

in acid solutions no precipitate is formed, if the free acid present 
vG one of the stronger acids. 

3. Hydro.su Iph u ret of ammonia throws down from neutral as 
iulphuretted hydrogen does from alkaline solutions, all the zinc 
ihey contain, as sulphuret of zinc, in the form of a white pre- 
ipitate. This precipitate is not redissolved by liydrosulphuret 
f'f ammonia in excess, nor by potash or ammonia ; it is sparingly 
oluble in hydrochloric acid, but easy of solution in aqua regia. 

4. Potash and ammonia throw down from solutions of zinc, 
iydrated oxide of zinc (Zn 0, HO) in the form of a white 
gelatinous precipitate, which is easily and completely redissolved 
oy an excess of the precipitant. 

5. Carbonate of potash produces a precipitate of basic car- 
bonate of zinc 3(Zn O, HO) + 2(Zn 0, C0 2 ) which is inso- 
nble in an excess of the precipitant. The presence of salts of 
ammonia prevents its formation, or they redissolve it when already 
cbrmed, giving rise to the formation of double salts of oxide of 
rinc and ammonia. 

6. Carbonate of ammonia produces the same precipitate as 
carbonate of potash ; addition of carbonate of ammonia in excess 
•edissolves it. 

1 7. Oxide of zinc, or a salt of oxide of zinc mixed with carbo- 
nate oj soda, and exposed to the reducing flame of the blow-pipe, 
covers the coal support with an incrustation of oxide of zinc, 
presenting a yellow colour, as long as it is hot, and changing to 
.vliite, on cooling. This is caused by the reduced metallic zinc 
volatilizing at the moment of its reduction, and rcoxidizing in 
oassing through the outer flame. 

8. 11 oxide of zinc, or a salt of zinc, be moistened with solution 
of proion it rate of cobalt , and heated before the blow-pipe, an un- 
:used beautifully green coloured mass is obtained, consisting of 
• i combination ol oxide of ziuc with protoxide of cobalt. 


02 


PROTOXIDE OF MANGANESE. 


b. PROTOXIDE OF MANGANESE. (Mn 0.) 

1. The protosalts of manganese are colourless or of a pale red; 
some of them are soluble, others insoluble. The soluble salts aro 
decomposed by a red heat, with the exception of protosulplmte of 
manganese. The solutions of the manganese salts do not alter 
vegetable colours. 

2. Sulphuretted hydrogen does not precipitate acid nor neutral 
solutions of protoxide of manganese. 

3. Hydrosulpliuret of ammonia throws down from neutral so- 
lutions, as sulphuretted hydrogen does from alkaline, all the man- 
ganese they contain, as sulphuket of manganese (Mn S) in the 
form of a bright flesh-coloured precipitate, which changes to a 
dark-brown when exposed to the air ; this precipitate is insoluble 
in hydrosulpliuret of ammonia and in alkalies, but easily soluble 
in hydrochloric acid and nitric acid. 

4. Potash and ammonia produce whitish precipitates of 
HYDRATED PROTOXIDE OF MANGANESE, (Mn 0, IIO,) which, when 
exposed to the air, soon change to a brownish, and at last to a 
dark blackish brown colour, owing to the hydrated protoxide being 
converted into hydrated peroxide, by the absorption of oxygen from 
the air. Ammonia and carbonate of ammonia do not redissolve 
this precipitate ; but sal ammoniac prevents the precipitation by 
ammonia completely, and that by potash partly. Solution of sal 
ammoniac redissolves only those parts of the already-formed pre- 
cipitates which have not yet undergone a higher degree of oxida- 
tion. The solution of the hydrated protoxide in sal ammoniac 
depends on the disposition of the protosalts of manganese to form 
double salts with salts of ammonia. The pellucid solutions of 
these double salts become brown, when exposed to the air, and 
depose dark-brown peroxide of manganese. 

5. If any compound of manganese be fused with carbonate of 
soda , on a platinum wire, in the outer flame, manganate of 
soda is formed, which makes the test specimen appeal - green, as 
long as it is hot, but, after cooling, of a bluish green and opaque. 
This reaction enables us to detect the smallest quantities of man- 




OXIDE OF NICKEL. 


93 


iWnese. Tlie delicacy of the test is still further increased if a 
j: miute quantity of nitre is added to the carbonate of soda. 

6. Borax and phosphate of soda and ammonia dissolve man- 
ganese compounds, in the outer flame of the blow-pipe, giving 
• ise to the formation of clear and violet-red glasses, which, on 
ooling, appear of an amethyst red, and lose their colour when 
Deposed to the inner flame, owing to the peroxide becoming re- 
duced to protoxide. The glass which borax forms with man- 
ganese, appears black when containing a considerable proportion 
of peroxide of manganese, but the glass formed by phosphate of 
»oda and ammonia never loses its transparency. The latter, when 
exposed to the inner flame, becomes colourless far more easily 
.ban the former. 

C . OXIDE OF NICKEL. (Ni 0.) 

1 . The salts of nickel are yellow or green ; their solutions are 
of a bright green colour. The soluble neutral salts redden litmus 
[paper and .are decomposed at a red heat. 

2. Sulphuretted hydrogen precipitates neither acid nor neutral 
-solutions of nickel ; or the latter at least but very incompletely. 

3. Hydrosulphuret of ammonia produces in neutral, as sul- 
phuretted hydrogen does in alkaline solutions, a black precipitate 
of sulpiiuret of nickel, (Ni S,) which is not altogether inso- 
luble in hydrosulphuret of ammonia, owing to which property the 
fluid from which it has been precipitated, presents always a brown- 
ish colour. Sulphuret of nickel is dissolved with difficulty by 
hydrochloric acid, but easily by aqua regia. 

4. Potash produces a bright green precipitate of hydrated 
oxide of nickel, (Ni O, HO,) which is insoluble in potash, and 
does not alter when exposed to the air. Carbonate of ammoni ft 
re-dissolves this precipitate to a greenish -blue fluid, from which 
[potash again precipitates the nickel it contains, as a yellow-green 
! hydrated oxide of nickel. 

5. Ammonia precipitates also hydrated oxide of nickel, 
but an excess of the precipitant easily re-dissolves it to a blue 


94 


PROTOXIDE OF COBALT. 


fluid, as a double salt of oxide of nickel and ammonia. Potash 
precipitates hydrated oxide of nickel from this solution. 

6. Cyanide of potassium produces a yellowish-green precipi- 
tate of cyanide of nickel, (Ni Cy,) wliich by an excess of the 
precipitant is easily redissolved to a brownish-yellow fluid, con- 
taining cyanide of nickel and cyanide of potassium combined. 
Sulphuric acid and hydrochloric acid again precipitate from this 
solution cyanide of nickel, which is very difficultly soluble in an 
excess of these acids, at a low temperature. 

7. Borax and phosphate of soda and ammonia dissolve com- 
pounds of oxide of nickel, in the outer flame of the blow-pipe, 
giving rise to the formation of clear glasses of a dark yellow 
colour, with a tinge of red-brown, which become clearer and 
almost colourless on cooling. Addition of nitre or carbonate of 
potash changes the colour to blue or to dark purple. The glass 
which phosphate of soda and ammonia forms with nickel remains 
unaltered when exposed to the inner flame, but that of borax 
becomes grey and troubled owing to the reduction of nickel. 

d. PROTOXIDE OF COBALT. (Co O.) 

1. The protosalts of cobalt are blue in their anhydrous, and of 
a characteristic bright red tint in their hydrated state. Their 
solutions show their colour even when considerably diluted. The 
soluble neutral salts redden litmus paper, and are decomposed by 
a red heat. 

2. Sulphuretted hydrogen does not precipitate acid solutions 
of cobalt, and neutral solutions at the most, very incompletely, 
when they contain weak acids ; these latter precipitates are of a 
black colour. 

3. Hydrosulphuret of ammonia precipitates from neutral, as 
sulphuretted hydrogen does from alkaline solutions, all the cobalt 
they contain, as black sulphuret of cobalt. (Co S.) This 
substance is insoluble in alkalies and hydrosulphuret of ammonia, 
difficultly soluble in hydrochloric acid, easily soluble in aqua 
regia. 




PROTOXIDE OF IRON. 


95 


4. Potash produces in solutions of cobalt blue precipitates of 
,xsic salts of cobalt, which become green when exposed to the 

i.T, owing to the absorption of oxygen, and are converted into 
vdrates of a pale red colour when boiled. They are insoluble in 
otash. But neutral carbonate of ammonia dissolves them com- 
letely to intensely violet-red fluids, in which potash does not 
ause any, or at least but a very scanty, precipitate. 

5. Ammonia produces the same precipitate as potash, but an 
\scess of the precipitant redissolves it to a reddish-brown fluid, 

i which potash does not cause any, or at least but a very scanty, 
precipitate. 

6. If to a solution of cobalt acidified with some hydrochloric 
cid, cyanide of potassium be added, a brownish -wliite precipitate 
f protocyanide of cobalt is formed, which by an excess of the 

precipitant, with presence of free hydrocyanic acid, is easily dis- 
olved to cobaltocyanide of potassium. (Cy6 C 02 + 3 K.) 
ucids cause no precipitation in the solutions of this salt. 

7. Borax dissolves compounds of cobalt in the inner as well as 
tu the outer flame of the blow-pipe, to clear splendidly blue 

oloured glasses which appear almost black, when cobalt is 
rresent in any considerable proportion. This test is as delicate as 
. is characteristic. Phosphate of soda and ammonia manifest the 
iame reaction, but in a lesser degree. 

e. protoxide of iron. (Fe 0.) 

1. The protosalts of iron have a greenish colour ; their solu- 
tions appear coloured only when quite concentrated. The soluble 

eutral salts redden litmus paper and are decomposed by a red 
: eat. 

2. Acid solutions are not precipitated by sulphuretted hydrogen, 
nd neutral solutions, with weak acids, at the most but incom- 

i. letely ; these precipitates are of a black colour. 

3. Hydrosulpkuret of ammonia precipitates from neutral, as 
sulphuretted hydrogen does from alkaline solutions, all the iron 
hey contain, as black sulphuret of iron, (Fe S,) which is 

6 


90 


PEROXIDE OF IRON. 


insoluble in alkalies and alkaline sulphurets, but easy of solution 
in hydrochloric acid and nitric acid. 

4. Potash and ammonia produce a precipitate of hydrated 
protoxide of iron, (Fe O, HO,) which, in the first moment 
appears almost white, but, after a very short time, becomes of a dirty 
green, by absorption of oxygen from the air, and at last assumes 
a red-brown colour. The presence of salts of ammonia prevents the 
precipitation by potash partly, and that by ammonia totally. 

5. Ferrocyanide of potassium produces in solutions of pro- ■{ 
toxide of iron a bluish-white precipitate of ferrocyanide of 
potassium and iron, (2 Cfy + Iv + 3 Fo,) which, by absorption 
of oxygen from the air, soon becomes blue. In this change, all 
the potassium of three equivalents of the compound, and one 
equivalent of iron, become oxidized, and Prussian blue (3 Cfy + 2 
Fe 2 ) remains. Nitric acid or chlorine causes this oxidation im- 
mediately. 

0. Ferricyanide of potassium produces a splendidly blue pro- : 
cipitate of ferricy’Anide of iron, (2 Cfy + 3 Fe.) This pre- 
cipitate does not differ in colour from Prussian blue. It is in- 
soluble in hydrochloric acid, but easily decomposed by potash. 
When the solution of protosalt of iron is highly dilute, the reagent ; 
imparts to it only a dark bluish green colour. 

7. Borax dissolves protosalts of iron in the oxidizing flame, 
forming deep red glasses, the colour of which changes to 
bottle green when exposed to the inner flame, owing to the re. 
duction of the first formed peroxide to magnetic-oxide. Both tints 
disappear totally, or in a great measure, when the glasses become ; 
cool. Phosphate of soda and ammonia shows a similar relation 
to the protosalts of iron, but the colour of its glass vanishes even 
more decidedly than is the case with borax. 

f. peroxide of iron. (Fe 2 O 3 ') 

1 . The persalts of iron are of a more or less red yellow colour. 
Their solutions present this colour even when pretty highly 
diluted. The soluble neutral salts redden litmus paper and are 
decomposed by heat. 


PEROXIDE OF IRON. 


07 


2. Sulphuretted hydrogen produces in neutral and acid sol li- 
ons a slight precipitate of sulphur, which renders the solution 

iirbid and imparts a milky white tint to it. Peroxide of iron and 
ulphuretted hydrogen decompose each other ; in this process, 
le hydrogen withdraws from the peroxide of iron, one-third of 
-s oxygen combining with it to form water ; the persalt of iron 
i thus converted into a protosalt, and the sulphur of the decom- 
i osed sulphuretted hydrogen separates. 

3. Hydros u Iph it ret of ammonia precipitates from neutral, as 
ulphuretted hydrogen does from alkaline solutions, all the perox- 

e of iron they contain, as black sulphuret of iron ; this pre- 
pitation is preceded by the conversion of the persalt into a proto- 
,lt. The reagent produces only a blackish-green tint in the 
lid, if the solution is very dilute. The minutely divided sul- 
mret of iron subsides in such cases only after the lapse of some 
ne. For the several degrees of solubility of sulphuret of iron in 
rious substances, vide e. (Protoxide of iron.) 3. 

4. Potash and ammonia produce bulky red-brown precipitates 
i hydrated peroxide of iron, which are insoluble in an excess 
I the precipitant, as well as in salts of ammonia. 

•5. Ferrocyanide of potassium produces even in highly dilute 
lutions a splendidly blue precipitate of sesquiferrocyanide 
iron, (3 Cfy-f 4 Fe,) (prussian blue) which is insoluble in 
idrochloric acid, but easily decomposed by potash, with preci- 
ation of peroxide of iron. 

G. Ferricyanide of potassium imparts a reddish-brown tint to 
lutions of peroxide of iron, but it causes no precipitate. 

7. The persalts of iron present the same appearances as the 
otosalts, when exposed to the action of the blow-pipe flame, 
le e. (protoxide of iron,) 7. 

Recapitulation and remarks. — Of the metallic oxides belonging 
the fourth group, oxide of zinc alone is soluble in potash. It 
this property which distinguishes it from the other oxides of 
-s group, and connects it with those of the third group. But it 
Ters from oxide of chromium and from alumina, inasmuch as 

n 




0 8 


PEROXIDE OF IRON. 


sulphuretted hydrogen precipitates it from its solutions in potash. 
This characteristic property is the surest test of oxide of zinc. 
Protoxide of manganese, oxide of nickel, protoxide of cobalt, and 
protoxide of iron form with salts of ammonia double salts, from 
which the metallic oxides are not precipitated by free ammonia: 
but peroxide of iron, just like the oxides of the third group, is 
completely precipitated by ammonia, even when salts of ammonia 
are present. Hence it follows, in the first place, that by means 
of this property, manganese, nickel and cobalt may be separated, 
as well from peroxide of iron as from oxide of chromium and from 
alumina ; and, in the second place, that, in order to separate these 
metals from protoxide of iron, the latter substance must first bo 
peroxidized, which operation is best performed by boiling its solu- 
tion with nitric acid. The peroxide of iron differs from oxide of 
chromium, and from alumina, inasmuch as it is insoluble in potash ; 
and peroxide of iron may be distinguished from protoxide, by 
means of ferrocyanide of potassium. Hydrated oxide of nickel 
and hydrated protoxide of cobalt dissolve in carbonate of ammo- 
nia, whilst hydrated protoxide of manganeso is insoluble in this 
substance. We may, therefore, by means of this solvent, separate 
the protoxide of manganeso from the two other oxides. The 
brown tint assumed by the white hydrated protoxide when ex- 
posed to the air, and the blow-pipe reactions, especially that with 
soda, are the surest test of protoxide of manganese. Cyanide of 
nickel, and cyanide of cobalt are soluble in cyanide of potassium. 
But cyanido of nickel may be precipitated from this solution by 
acids, which is not the case with cyanido of cobalt. This pro- 
perty, i. e. the formation of a precipitate in a solution of these two 
cyanides in cyanide of potassium, by the addition of hydrochloric 
acid, is under all circumstances a perfectly sure test of the presence 
of nickel. Whether thisprecipitate be cyanide of nickel or cobalti- 
cyanide of nickel, is quite immaterial as far as the detection of 
nickel is concerned ; we have only to bear in mind that no preci- 
pitate forms if cobalt alone be contained in the solution, since 
cobalticyanide of potassium is not decomposed by hydrochloric 
acid. To explain the composition of the precipitates formed, and 


FEROXIDE OF IRON. 


99 


ae process in general, we will now proceed to consider and ex- 
mine three special cases, the difference of which depends on the 
nequal relative proportion of the nickel and the cobalt. 

1, Ni : Co = 3 eq. : 2 eq. 

2, Ni : Co = 3 eq. I 2 eq. + x 

3, Ni \ Co — 3 eq. + x • 2 eq. 

onsequently, we get in solution in the first case, one eq. : of cobal- 

lyanide of potassium, (Cy 6 , Co 2 + 3 K,) and 3 eq. : of cyanide 
‘nickel and cyanide of potassium combined, (Cy 3 Ni, + Cy 3 K,) 
id if we add hydrochloric acid in excess to this solution, we 
otoin a dirty green precipitate of cobalticyanide of nickel 
jy 6 Co 2 + 3 Ni,) which contains all the nickel and cohalt of 
e solution ; in this process the combination of cyanide of 
ckel and cyanide of potassium is decomposed, and the potassium 

the cobalticyanide of potassium changes places with the nickel 
tho cyanide of nickel. Besides the cobalticyanide of nickel, 
loride of potassium and hydrocyanic acid aro formed. In the 
cond case we obtain also a precipitate of cobalticyanide of 
ckel, hut this precipitate, though containing all the nickel, does 
•>t contain all the cobalt of the solution, for the excess of cobalti- 
lanido of potassium is not decomposed. In the third case, at 
rBt, we obtain a precipitate of cobalticyanide of nickel, which 
i ntains all the cobalt and a portion of the nickel, mixed with in- 
: lublo cyanide of nickel, which contains the remaining part of 
i e nickel. The precipitate of cobalticyanide of nickel has been 
rmed, as in the first case, whilst the cyanide of nickel is formed 
the decomposition of the double cyanido of nickel and po- 
Msium in excess. Hence it is evident, that nickel is in all cases 

I iecessary condition to the formation of a precipitate, and con- 
quently that this precipitate can leave no doubt as to its pre- 
ice. As cobalt may, under all circumstances, be safely and 
idly detected by its characteristic properties before the blow- 
oe, any further indications for the mere detection of either 
fctal, would almost seem superfluous; but since we are now 
oady far advanced towards the complete separation of these two 
istances from each other, we may as well briefly state how to 

h 2 


100 


OXIDE OF SILVER, &C. 


effect it. In the first, and second of the above-men tioned eases, 
we have, after tho addition of the hydrochloric acid, only to heat 
the fluid together with the therein suspended precipitate of cohalti- 
cyanide of nickel, till the free hydrocyanic acid is expelled, (the 
cohaltioyanide of nickel as well as the cohalticyanide of potassium 
present in the second case, remain unaltered during this opera- 
tion ;) and then we may, hy addition of caustic potash, easily de- 
compose the cohalticyanide of nickel, into cohalticyanide of potas- 
sium, which remains in solution, and oxide of nickel which preci- 
pitates as hydrated oxide. But in the third case we must add a 
larger quantity of hydrochloric acid, and boil the solution there- 
with, till the cyanide of nickel contained in the precipitate (which 
would only be incompletely decomposed hy potash) is converted 
into chloride of nickel, and till the hydrocyanic acid, formed 
during this operation, is completely expelled ; and then, after this 
preparatory process, we may, hy boiling with caustic potash, 
obtiun all the nickel ns an insoluble hydrated oxide, and all the 
cobalt as soluble cohalticyanide of potassium. Lastly, we must 
still mention, that the oxides of the fourth group are not preci- 
pitated hy alkalies, if non-volatile organic substances, (such as 
sugar, tartaric acid, &c.) are contained in their solutions. The 
same is the case with alumina and oxide of chromium. 

§ 89 . 

Fifth Group. 

OXIDE OF SILVER, PROTOXIDE OF MERCURY, PEROXIDE OF MEM 
CURY, OXIDE OF LEAD, OXIDE OF BISMUTH, OXIDE OF 
COPPER, OXIDE OF CADMIUM. 

Properties of the group . — The sulphurets corresponding with 
the oxides of this group, arc insoluble both in dilute acids and in 
alkaline sulphurets. The solutions of these oxides are therefore 
completely precipitated by sulphuretted hydrogen, no matter 
whether their reaction be neutral, alkaline, or acid. 

We divide the oxides of this group into two sections, and di$i 
tinguish 


OXIDE OF SILVER. 


101 


1. Oxides precipitable by hydrochloric acid, viz.: 
xxido of silver, protoxide of mercury, imd oxide of lead, from 

2. Oxides, not precipitable by hydrochloric acid, viz. : 
eroxide of mercury, oxide of copper, oxide of bismuth, oxide of 

; idmium. Lead must be considered in both sections, as the diffi- 
i lit solubility of its chloride renders it possible to confound it 
ith protoxide of mercury and oxide of silver, without affording us 
tuy means of separating it completely from the oxides of the 
;cond section. 

§ 90. 

IRST SECTION. OXIDES PRECIPITABLE BY HYDROCHLORIC ACID. 

Special Reactions. 

a . OXIDE OF SILVER. (Ag O.) 

I. The salts of oxide of silver are fixed and colourless ; most 
them blacken when exposed to light. The soluble neutral 
Its do not alter vegetable colours, and are decomposed at a red 
iat. 

•2. Sulphuretted hydrogen and hydrosulphuret of ammonia 
j-ecipitato black sulpiiuret of silver, (Ag S,) which is 
'Soluble in dilute acids, alkalies, alkaline sulphurets, and 
tranide of potassium. Boiling concentrated sulphuric acid 
sily decomposes and dissolves this precipitate, with separation 
sulphur. 

3. Potash and ammonia precipitate oxide of silver, in the 
rm of a bright brown powder, which is insoluble in potash, 
it easy of solution in ammonia. The presence of salts of arn- 
onia prevents this reaction either totally or partly. 

4. Hydrochloric acul and soluble chlorides produce a white 
rdv precipitate of chloride of silver. (Ag Cl.) In very 
ute solutions, this precipitate merely imparts to the fluid a 
.fish-white opalescent appearance. The white chloride of silver, 
len exposed to light, acquires first a violet tint, and at last a 


102 


PROTOXIDE OF MERCURY. 


black colour, but without any alteration in its composition ; it is 
insoluble in nitric acid, but dissolves easily in ammonia, giving 
rise to the formation of chloride of silver and ammonia. Acids 
precipitate it again from this combination. Chloride of silver, 
when heated, fuses without decomposition, forming a transparent 
horny mass. 

5. When silver compounds, mixed with carbonate of soda, are 
on a charcoal support, exposed to the inner flame of the blow- 
pipe, WHITE, SHINING, AND DUCTILE METALLIC GLOBULES OTO 
obtained, whilst no incrustation takes place. 

b. PROTOXIDE OF MERCURY. (Hg 2 0.) 

1. The salts of protoxido of mercury, when exposed to a red 
heat, either volatilize without decomposition, or decompose ; in 
the hitter case the mercury separated volatilizes in a metallic state. 
They are colourless. The soluble salts, when neutral, redden 
litmus paper; when mixed with much water, they separate into 
insoluble basic and soluble acid salts. 

2. Sulphuretted hydroyen and hydrosu Iph uret of ammonia 
produce black precipitates of sulphuret of mercury, (I:Ig 2 S,) 
which are insoluble, as well in dilute acids as in alkaline sulphu- 
rets, and in cyanide of potassium. Potash resolves this sulphuret 
into bisulphuret and globules of metallic mercury. Sulphuret 
of mercury is easily decomposed and dissolved by aqua regia, but 
not by boiling concentrated nitric acid. 

3. Potash and ammonia produce black precipitates, which are 
insoluble in an excess of the precipitants. The potash precipi- 
tates consist of protoxide of mercury ; those of ammonia, of a 
BASIC SALT OF PROTOXIDE OF MERCURY AND AMMONIA. 

4. Hydrochloric acid nnd soluble chlorides precipitate proto- 
chloride of MERCURY (Hg 2 Cl) as a shining white, fine powder. 
Cold hydrochloric acid, and cold nitric acid, do not dissolve this 
precipitate ; but it dissolves, although very difficultly and slowly, 
when long boiled with these acids, being converted by hydro- 
chloric acid into chloride of mercury, by nitric acid into chloride 
of mercury and per-nitrate of mercury. Ammonia and potash 


OXIDE OF LEAD. 


103 


decompose protocliloride of mercury, giviug rise to the formation 
jf black protoxide of mercury. 

5. If a drop of n neutral or feebly acid solution of protoxide of 
mercury be poured on a clean and smooth surface of copper, 
i vashed off after some time, and the spot rubbed with cloth or 
japer, &c. &c., it will appeal - of a silvery white colour, with 
metallic lustre. This apparent silvering vanishes when the 
copper is heated, owing to the volatilization of the metallic mer- 
cury precipitated on its surface. 

0. Protochloride of tin produces in solutions of protoxide of 
mercury, a grey precipitate of metallic mercury, which may be 
ini ted into globules by heating and agitating it, hut most easily 
ly boiling it with hydrochloric acid. 

7. If mercury compounds, intimately mixed with effloresced 
•tarbonate of soda, and covered with a layer of carbonate of soda 
n a distended glass- tube, are heated before the blow-pipe, a de- 
composition always takes place to the effect of liberating mctidlic 
mercury, which sublimes as a grey crust above the heated part of 
he tube. The fine particles of mercury unite into globules on 
'his crust being rubbed with a glass rod. 

C. OXIDE OF LEAD. (Pb 0.) 

1. The salts of oxide of lead are colourless and not volatile ; 
lie soluble salts, when neutral, redden litmus paper, and are de- 
:omposed at a red heat. 

2. Sulphuretted hydropen and hydrosulphuret of ammonia 
produce black precipitates of sulpiiuret of lead, (Pb S,) which 
ire insoluble in dilute acids, idkalies, alkaline sulphurets, and 
cyanide of potassium. This sulpiiuret of lead is decomposed by 
coiling concentrated nitric acid ; all the lead is first converted 
nto nitrate of lead, the greater portion of the sulphur separates, 
mother portion is converted into sulphuric acid, and this again 
lecomposes a part of the nitrate of lead, and thus, besides the 
precipitated sulphur, sulphate of lead is formed, and remains un- 
lissolved as a wliite powder. 

3. Potash and ammonia throw down basic salts of lead in 


104 


OXIDE OF LEAD. 


the form of white precipitates, which are insoluble in ammonia, 
mul of difficult solution in potash. 

4. Hydrochloric acid and soluble chlorides produce in con- 
centrated solutions heavy white precipitates of chloride of lead, 
(Pb Cl,) which arc soluble in much water, especially if the water 
be heated. This chloride of lead is not altered by ammonia, and 
is more difficult of solution in hydrochloric acid and in nitric acid 
than in water. 

5. Sulphuric acid and sulphates produce white precipitates of 
sulphate of lead, (Pb O, S0 3 , ) which are almost insoluble in 
water and dilute acids, but to a small extent soluble in concen- 
trated nitric acid, difficult of solution in boiling concentrated 
hydrochloric acid, and more easily soluble in solution of potash. 
Salts of ammonia, mid especially sulphate of ammonia, prevent 
the precipitation partly or altogether. 

0. Chromate of potash produces a yellow precipitate of chro- 
mate of lead, (Pb O, Cr 0 3 ) which is easily soluble in potash, 
hut insoluble in dilute nitric acid. 

7. Lead compounds, mixed with carbonate of soda, and on a 
charcoal support, exposed to the reducing blow-pipe flame, very 
easily yield soft and ductile metallic globules ; whilst the coal 
is, at the same time, covered with a yellow incrustation of oxide 

OF LEAD. 


Recapitulation and remarks . — The metallic oxides of the first 
section of the fifth group are the most easily characterized iu 
their corresponding chlorides, since the divers relations of these ! 
different chlorides to ammonia afford us means as well of detect- 
ing as of separating them from each other. For chloride of 
silver, as we have stated, is dissolved by ammonia, whilst protochlo- 
ride of mercury and chloride of lead remain undissolved. By add- I 
ing nitric acid to a solution of chloride of silver and ammonia, we ! 
may again precipitate the chloride of silver; and as tins reaction | 
admits of no mistake, we want in fact no further means for the 9 
detection of silver. Of the two remaining chlorides, the protocldo- V 


ride of mercury is converted by ammonia into black protoxide of 1 




PEROXIDE OF MERCURY. 


105 


i mercury, whilst the chloride of lead remains unaltered, llie 
i new-formed protoxide of mercury may be separated from the 
i chloride of lead by treating with nitric acid, whereby the prot- 
oxide of mercury is dissolved ; or by boiling with water, when 
•solution of the chloride of lead takes place. These relations 
sufficiently characterize the protoxide of mercury ; as further 
tests for lead, its reaction with sulphuric acid or with chromate of 
potash may be employed. 


§ 91 . 

SECOND SECTION OF THE FIFTH GROUP. OXIDES WHICH ARE NOT 
PRECIPITATED BY HYDROCHLORIC ACID. 

Special Reactions. 

a. PEROXIDE OF MERCURY. (Hg 0.) 

1 . The salts of peroxide of mercury volatilize when heated to 
redness, some with, some without decomposition. Most of them 
are colourless. The neutral soluble salts redden litmus paper. 
The nitrate and sulphate of peroxide of mercury are decomposed 
by much water into soluble acid and insoluble basic salts. 

2. If sulphuretted hydrogen , or h ydrosulph u ret of ammonia, 
be added in very small proportions to solutions of peroxide of 
mercury, and these solutions be then agitated, a perfectly white 
precipitate is obtained. The addition of somewhat large quan- 
tities of these reagents causes the precipitate to acquire a yellow, 
orange, or brown-red colour, as more or less of them is added ; 
an excess of the precipitate produces a black precipitate of 
bisulphuret of mercury, cinnabar. (Hg S.) This varia- 
tion of colour depends on the different proportions added of 
sulphuretted hydrogen, distinguishing the peroxide of mer- 
cury from all other substances. It is caused by the formation, 
at first, of a white-coloured double compound of bisulphuret of 
mercury, with still uudecomposed salt of peroxide of mer- 
cury, which then, becoming more and more mixed with black 


100 


PEROXIDE OF MERCURY. 


bisulphuret, causes the precipitate successively to assume the various 
tints described above. Bisulphuret of mercury is not dissolved by 
hydrosulphuret of ammonia, nor by cyanide of potassium ; it is 
quite insoluble in hydrochloric acid and nitric acid, even on beiiq 
boiled with these acids. Potash ley dissolves it completely, and 
aqua regia decomposes and dissolves it with facility. 

3. Potash, when added in insufficient quantity to neutral or 
feebly acid solutions of peroxide of mercury, yields with them a red- 
broyvn precipitate, which acquires a yellow tint when the re- 
agent is added in excess. The red-brown precipitate is a basic 
salt ; the yellow, on the contrary, consists of pure hydrated 
PEROXIDE OF MERCURY. (Hg O, HO.) An excess of the preci- 
pitant does not re-dissolve these precipitates. In very acid solu- 
tions this reaction either does not take place at all, or is at least 
incomplete. If salts of ammonia bo present, the precipitates 
formed ore neither red, brown, nor yellow, but white ; consisting 
of basic compounds of peroxide of mercury and ammonia. 

4. Ammonia causes the same white precipitate, which potash 
produces when salts of ammonia are present. 

5s Protochloride of tin, when added in small proportions to salts 
of peroxide of mercury, causes a reduction of this peroxide to prot- 
oxide, inconsequence of which a white precipitate of protochloride 
of mercury forms ; but when added in excess, it completely 
withdraws the oxygen and acid or the salt-radical from the mer- 
cury, and causes the latter to separate in a metallic form, just as is 
the case with protoxide of mercury, (vide § 90, b 6.) The preci- 
pitate, therefore, which in the first place was white, acquires now 
a grey tint, and may be united into globules of metallic mercury, 
by being boiled with hydrochloric acid. 

5. The salts of peroxide of mercury present the same relation 
to metallic copper as those of the protoxide ; and the same is the 
case with regard to their behaviour before the blow-pipe, when 
mixed with carbonate of soda. 


OXIDE OF COPPER. 


107 


b. OXIDE OF COPPER. (Cu 0.) 

1. The salts of oxide of copper undergo decomposition, even 
at a gentle red heat, -with the exception of blue vitriol, which can 
bear a somewhat higher temperature. They present in their an- 
hydrous state a white, hut as hydrates, a blue or green colour, 
which their solutions still retain, though rather highly diluted. 
Most of the neutral salts of oxide of copper are soluble in water ; 
those which are soluble redden litmus paper. 

2. Sulphuretted hydrogen and hydrosulphuret of ammonia pro- 
duce, under any circumstances, brown-black precipitates of bisul- 
phuret of copper (Cu S.) This substance is insoluble in dilute 
acids and caustic alkalies, as well as in hot solutions of sulphuret 
of potassium and of sulphuret of sodium ; but it is not quite in- 
soluble in hydrosulphuret of ammonia, on account of which this 
reagent is not applicable for the separation of bisulphuret of copper 
from other metallic sulphurets. Boiling concentrated nitric acid 
readily decomposes and dissolves bisulphuret of copper. Solu- 
tion of cyanide of potassium dissolves it completely. 

3. Potash produces a bright blue, bulky precipitate of 
hydrated oxide of copper, (Cu 0, HO.) In highly concen- 
trated solutions this precipitate becomes, on addition of potash in 
excess, black, and loses its bulkiness, even at a low temperature, 
after some time, but at any rate on being boiled with the fluid 
wherein it is suspended. In this process the hydrated oxide is 
converted into oxide. 

4. Ammonia, when added in a small proportion, produces a 
greenish blue precipitate, consisting of a basic salt of copper. 
This precipitate is easily redissolved when the addition of ammonia 
is continued, and a perfectly transparent magnificently 
azure blue solution obtained, which owes its colour to the new- 
formed BASIC AMMONIACAL SALT OF OXIDE OF COPPER. Tllis tint 
vanishes only when the solution is highly diluted. Potash causes 
in this blue solution — (at a low temperature only after having been 
allowed to stand at rest for some time) — a precipitate of blue 


JOB 


OXIDE OF BISMUTH. 


HYDRATED oxide, but nt the boiling point, it precipitates the en- 
tire copper as black oxide. Carbonate of ammonia presents the 
same relation to salts of copper, as pure ammonia. 

5. Ferrocyanide of potassium produces even in highly- dilute 
solutions, a reddish-brown precipitate of ferrocyanide of copper 
(Cfy + 2Cu) which is insoluble in dilute acids, but decomposed 
by potash. 

0. Metallic iron, when in contact with concentrated solutions 
of copper, is almost immediately covered with a coppery red 
crust of metallic copper ; but when the copper solution is 
highly dilute, this coating only takes place after the lapse of some 
time. This test is very delicate, but especially so, when the solu- 
tion contains a free acid, (e. g. hydrochloric acid.) 

7. If copper compounds, mixed with carbonate of soda, bo ex- 
posed on a charcoal support to the reducing flame of the blow- 
pipe, metallic copper is obtained without simultaneous incrus- 
tation of the coal. The best method of examining this copper, so 
as to leave no doubt of its presence, is to triturate the fused mass 
together with the surrounding particles of the charcoal support, in 
a mortar with some water, and then to wash off the charcoal 
powder. The coppery-red metallic spangles will remain. 

c. oxide of bismuth. (Bi 0.) 

1. The salts of bismuth are not volatile, with the exception of 
a few, (chloride of bismuth.) Most of them decompose at a red 
heat. They are colourless ; some are soluble in water, whilst 
others are insoluble. The soluble salts, when neutral, redden 
litmus paper, and are decomposed by much water into soluble acid 
and insoluble basic salts. 

2. Sulphuretted hydrogen and hgdrosulphuret of ammonia 
produce, under all circumstances, black precipitates of sulphuret 
of bismuth (Bi S) which arc insoluble in dilute acids, alkalies, 
alkaline sulphurets, and cyanide of potassium. Boiling concen- 
trated nitric acid readily decomposes and dissolves it. 

3. Potash and ammonia throw down from solutions of salts of 


OXIDE OF CADMIUM. 


109 


bismuth, hydrated oxide of bismuth (Bi O, HO) as a white 
precipitate, which is insoluble in an excess of the precipitants. 

4. Chromate of potash precipitates chromate of bismuth 
(Bi O, Cr 0 3 ) as a yellow powder. This substance differs from 

• chromate of lead, inasmuch as it is soluble in dilute nitric acid, 
and insoluble in potash. 

5. The reaction which particularly characterizes the oxide of 
bismuth, is the decomposition of its neutral salts by water into 
acid soluble and basic insoluble salts. For when a solution of 
bismuth is diluted with much water, a shining wliite precipitate 
immediately forms, provided free acid be not present in a too large 
proportion. This reaction is the most susceptible with chloride of 
bismuth, the basic chloride of bismuth being almost absolutely in- 
soluble in water. If water causes no precipitate in nitric solutions 
of bismuth, owing to the presence of a too large quantity of free 
acid, precipitation may immediately be induced by the addition of 
basic acetate of lead in excess. Before recurring to this means, 
we must, of course, be convinced of the absence of sulphuric acid, 
&c. &c. The precipitates of bismuth are easily to be distinguished 
by means of their insolubility in tartaric acid, from the basic 
salts of antimony which are formed under analogous circum- 
stances. 

G. If bismuth compounds, mixed with carbonate of soda, be ex- 
posed on a charcoal support, to the reducing flame, brittle grains 
of BISMUTH are obtained, which fly into pieces under the strobe 
of the hammer. The charcoul at the same time becomes covered 
with a slight yellow incrustation of oxide of bismuth. 

d. OXIDE OF CADMIUM. (Cd O.) 

1. The salts of oxide of cadmium are either colourless or white ; 
most of them are soluble in water. The soluble salts, when 
neutral, redden litmus paper and decompose at a red heat. 

2. Sulphuretted hydrogen and hydrosulphuret of ammonia 
produce, under all circumstances, precipitates of a rich yellow 
colour, consisting of sulphuret of cadmium (Cd, S.) This sub- 


1 10 


OXIDE OF CADMIUM. 


stance is insoluble in diluto acids, in alkalies, alkaline sulphurets, 
and cyanide of potassium. Boiling concentrated nitric acid readily 
decomposes and dissolves it. 

3. Potash produces a white precipitate of hydrated oxide op 
cadmium (Cd 0, HO) which is insoluble in an excess of the pre- 
cipitant. 

4. Ammonia also precipitates white hydrated oxide of cad- 
mium, but readily redissolves into a colourless fluid, when added 
in excess. 

5. Carbonate of potash and carbonate of ammonia produce 
white precipitates of cardonate of cadmium (Cd O, CO?) which 
are insoluble in an excess of the precipitants. The presence of 
salts of ammonia does not prevent the formation of these pre- 
cipitates. 

6. If cadmium compounds mixed with carbonate of soda be 
exposed on a charcoal support, to the reducing flame, the char- 
coal becomes covered with a reddish yellow incrustation of 
oxide of cadmium, owing to the reduced metal immediately vola- 
tilizing, and then becoming reoxidized in passing through the 
oxidizing flame. 

Recapitulation and remarks . — The metallic oxides of the 
second section of the fifth group may, as we have stated, be com- 
pletely separated, by means of hydrochloric acid, from protoxide 
of mercury and oxide of silver, but only incompletely from oxide 
of lead. The peroxide of mercury is distinguished from the other 
oxides of this section, by the insolubility of its bisulphuret in boil- 
ing nitric acid. This property affords a convenient means for its 
separation. Moreover, the reactions with protoxide of tin, or with 
metallic copper, as well as those in the dry way, readily admit of 
its detection when the protoxide has been previously removed. 

Of the still remaining oxides, those of copper and cadmium are 
distinguished, inasmuch as the precipitates which ammonia causes 
in their solutions, are soluble in an excess of ammonia, whilst the 
precipitates which this reagent produces in solutions of lead and 
bismuth, are not redissolved by an excess of the precipitant. The 


PEROXIDE OF GOLD, &C. 


1 1 1 


oxide of bismuth may be separated from the oxide of lead by 
>means of sulphuric acid, but is most safely detected by the de- 
composibility of its salts by water. The other tests of lead have 
a already been stated in the first section of this group. The oxide 
of copper may be separated from the oxide of cadmium, by means 
of carbonate of ammonia ; the former is especially characterized 
by the reactions with ferrocyanide of potassium and with iron, as 
well as by its relations before the blow-pipe ; and oxide of cad- 
imium may always be detected by its yellow sulphur et, which is 
: insoluble in hydrosulphuret of ammonia, and by the characteristic 
incrustration with which it covers charcoal when exposed to the 
r reducing flame. For a separation of the oxides of the fifth group 
: from each other, by means of cyanide of potassium, we refer to 
: the second section of Part II. 


§ 92 . 

Sixth Group. 

PEROXIDE OF GOLD, PEROXIDE OF PLATINUM, OXIDE OF ANTIMONY, 
PEROXIDE OF TIN, PROTOXIDE OF TIN, ARSENIOUS AND ARSENIC 
ACID.* 

Properties of the group . — The sulphurets corresponding with 
the oxides of the sixth group are insoluble in dilute acids. They 
combine with alkaline sulphurets, forming soluble sulphur salts 
in which compounds they perform the part of an acid. Sulphu- 
retted hydrogen, therefore, precipitates them completely from aci- 
dified, but not from alkaline solutions. The precipitated sul- 
phurets dissolvo in hydrosulphuret of ammonia, sulphuret of 

* The two acids of arsenic will be again referred to, when we treat of 
the relations between acids and reagents. We join them here to the me- 
tallic oxides, since the relation of sulphuret of arsenic easily admits of their 
being confounded with several oxides of the sixth group, and because in 
analysis we always obtain the sulphuret of arsenic as a precipitate, together 
with sulphuret of antimony, sulphuret of tin, &c. &c. 


G 


I 12 


PEROXIDE OF GOLD. 


potassium, Ac. &c., and arc again precipitated from these solu- 
tions by the addition of acids. 

We divide the oxides of this group into two classes, and dis- 
tinguish, 

1. OxrDES THE CORRESPONDING SULPHURF.TS OF WHICH ARE 
INSOLUBLE IN HYDROCHLORIC ACID AND IN NITRIC ACID, viz. 
peroxide of gold and peroxide of platinum, from 

2. Those the corresponding sulphurets of which are 

SOLUBLE IN HYDROCHLORIC ACID OR NITRIC ACID, viz. Oxide of 
antimony, protoxide and peroxide of tin, arsenious and arsenic 
acid. 

§ 93. 

First Class. 

Special Reactions, 
a. PEROXIDE OF GOLD. ( All 0 3 . ) 

1. Salts of gold with oxygen acids are at present almost un- 
known. The haloid salts of gold are yellow, and their solutions 
present this tint up to a high degree of dilution. They all readily 
decompose at a red heat; the soluble salts, when neutral, redden 
litmus paper. 

2. Sulphuretted hydrogen precipitates from neutral and acid 
solutions all the gold they contain, as black sulphuret of gold 
(Au S 3 ) which is insoluble in potash and in any single acid, but 
soluble in alkaline sulphurets and in aqua regia. 

3. Hydrosulphuret of ammonia produces the same precipitate. 
A considerable excess of the precipitant redissolves it. 

4. Potash in excess causes no precipitation, but a small pro- 
portion of potash produces in concentrated solutions, especially 
when heated, a reddish yellow precipitate of peroxide of gold, 
which is always mixed with an auric salt or chloride of gold, as 
well as with potash. 

6. Ammonia produces also only in concentrated solutions, 
reddish yellow precipitates of aurate of ammonia (fulminating 
gold.) 


PEROXIDE OF PLATINUM. 


IK} 


I 0. Protochloride of tin, containing perchloride of tin, produces 

1 'ven in highly dilute solutions of gold, u purple-red precipitate or 
:nt at least, which sometimes inclines more to violet or to brown-red. 
This precipitate has received the name of purple of Cassius ; it 
- i a mixture of peroxide of tin and metallic gold, and is insoluble 
i.i hydrochloric acid. 

7. Protosalts of iron reduce the peroxide of gold when added 
i ) its solutions, and precipitate metallic gold as a very fine brown 
ixiwder, which shows a metallic lustre, when pressed upon with 
itie blade of a knife, or when rubbed. The fluid in which the pre- 
i pitate is suspended, appears of a blackish-blue colour, by trans- 
litted light. 


If. PEROXIDE OF PLATINUM. ( Pt O*. ) 

1 . The persalts of platinum decompose at a red heat They 
re of a red-brown colour, which their solutions still show, though 
ionsiderably diluted. The soluble salts when neutral redden 
ttmus paper. 

2. Sulphuretted hydrogen precipitates from acid and neutral 
blutions — (but not from alkaline solutions) — after the lapse of 

1 Dme time blackish-brown sulpiiuret of platinum ( Pt S 2 . ) 
otash and alkaline sulphurets dissolve it when added greatly in 
Ucess. Sulphuret of platinum is iusoluble in hydrochloric 
bid as well as in nitric acid, but dissolves readily in aqua regia. 

3 Hydrosulphuret of ammonia produces the same precipitate, 
jlhich completely redissolves in a large excess of the precipitant, 
j cids precipitate it again unaltered from this solution. 

4. Potash and ammonia produce in solutions of platinum, when 
lot too highly dilute, yellow chrystalline precipitates of chloride 
r platinum and potassium and of chloride of platinum and 
mmonium, which are insoluble in acids, but soluble in an excess 
the precipitants, upon the application of heat. The presence 
free hydrochloric acid promotes the precipitation in a high de- 
K’ee, by effecting the conversion of the free alkalies into chlo- 
ities. 


1 


114 


OXIDE OF ANTIMONY. 


5. Protochloride of tin imparts an intense dark brownish red 
colour to solutions of persalts of platinum, but without yielding 
a precipitate ; this reaction is owing to a reduction of the peroxide 
or the perchloride to protoxide or protochloride. 

Recapitulation and remarks. — The reactions of gold and pla- 
tinum afford, at least partly, the means of detecting these metals 
as well when many other oxides are present, as also and espe- 1 
ciully, when platinum and gold are contained in one and the same 
solution. Protochloride of tin and protoxide of iron must be men- 4 
tioned here as particularly characteristic tests of gold, and with 
regard to platinum the same may be said of potash and ammonia 
with the presence of free hydrochloric acid, or what in fact is the 
same, of chloride of potassium and muriate of ammonia. 

Second Class of the Sixth Group. 

Special Reactions, 
a. oxide of antimony. ( Sb Ox ) 

1 . The salts of oxide of antimony partly decompose at a red 1 
heat ; the haloid salts volatilize readily, and without undergoing .. 
decomposition. The soluble neutral salts of antimony redden | 
litmus paper. The solution of oxide of antimony in hydrochloric I 
acid is characterized by the nature of the decomposition it under- 1 
goes when diluted with water ; in this decomposition, an acid salt re- 1 
mains in solution whilst a basic salt is thrown down as a white, f 
bulky precipitate, which, however, after some time, becomes dense } 
and chrystal line. Tartaric acid readily dissolves this precipitate, I 
and, consequently, prevents its precipitation when added to the 
solution before the dilution with water. It is by this property | 
that the basic protochloride of antimony is distinguished from the 
basic salts of bismuth formed under analogous circumstances. I 
The oxide of antimony, in whatever manner it may have been 


OXIDE OF ANTIMONY. 


J IT) 

prepared, is completely soluble in a hot solution ol bitartrate of 
potash. 

2. Sulphuretted hydrogen precipitates the oxide of antimony 
from neutral solutions very incompletely, from alkaline solutions 
aot at all, but from acid solutions completely as orange-red sul- 
phuretof antimony (Sb S 3 .) This precipitate is readily dissolved 
oy potash and by allvaline sulphurets, especially if the latter 
jontain sulphur in excess, whilst it is almost insoluble in am- 
monia, and totally so in bicarbonate of ammonia, when free from 
any admixture of sulphur, as well as from sulpliantimonious and 
mlphantimonic acid. It is insoluble in dilute acids. Concentrated 
ooiling hydrochloric acid dissolves it, with evolution of sulphu- 
retted hydrogen gas. When heated, with free access of air, it is 
converted into a mixture of antimonious acid with sulpliuret of 
antimony. When deflagrated with saltpetre, it yields sulphate of 
>otash and antimoniate of potash. If a potash solution of sul- 
ihuret of antimony be boiled together with oxide of copper, sul- 
ibhuret of copper is formed, and oxide of antimony dissolved in 
I'Otash remains in solution. 

3. Uydrosulphuret of ammonia produces an orange-red preci- 
itate of sulphurkt of antimony, wliich readily redissolves in an 
xxcess of the precipitant. Acids precipitate from this solution the 
ailphuret of antimony unaltered. But the colour of this second 
recipitato usually appears somewhat lighter, owing to an admix- 
are of sulphur. 

4. Potash, ammonia, carbonate of potash, and carbonate of 
mmonia, throw down from the solutions of simple salts of oxide 
if antimony, — but not, at least not immediately, from those of 
irtar emetic or analogous compounds, — a white and bulky preci- 
itate of HYDRATED OXIDE OF ANTIMONY (Sb 0 3 , HO) which 
eadily redissolves in an excess of potash, but is very difficult of 
dut.ion in an excess of the other three precipitants. 

5. Metallic zinc precipitates from all solutions of oxide of an- 
mouy, unless containing free nitric acid, metallic antimony as 
black powder. But if they contain free nitric acid, a precipi- 

1 2 


110 


OXIDE OF ANTIMONY. 


tftte of oxide of antimony forms simultaneously with the metallic 
precipitate. 

0. If a solution of oxide of antimony is mixed with zinc and 
sulphuric acid, the zinc oxidizes not only at the expense of the 
oxygen of the water, hut also at the expense of that of the oxide 
of antimony. Antimony, therefore, separates in its metallic 
state, hut a portion of the metal in the moment of its separation 
combines with the liberated hydrogen of the water, forming anti- 
moniuretted hydrogen ( Sb II 3 . ) If this operation be conducted 
in a gas-evolution flask, connected by means of a perforated cork 
with one limb of a bent tube, the other limb of which ends in a 
finely drawn-out point, pinched off at the top,*) and the hydrogen 
passing through this fine aperture, be kindled, after all atmo- 
spheric air has been previously expelled, the flame appears of a 
bluish-green, owing to the antimony separating in a state of intense ; 
heat, during the combustion of the antimoniuretted hydrogen ; white 
fumes of oxide of antimony rise from the flame, which readily con- 
dense upon cold substances, and are not dissolved by water. If a 
cold substance (such as a porcelain plate) be depressed upon the 
flame, a deep black and almost lustreless spot of metallic antimony 
in a state of minute division is formed upon the surface of the 
plate. If the tube through which the gas is passing be heated to 
redness in the middle, the bluish-green tint of the flame disap- 
pears, and a metallic mirror of antimony of silvery lustre is formed 
within the tube on both sides of the heated spot. If a stream of 
dry sulphuretted hydrogen be now very slowly transmitted through 
this tube, and the mirror be heated by a spirit-lamp, from its outer 
towards its inner extremity, i. e. in a direction opposite to that of 
the gas stream, the mirror of antimony changes into sulphuret of 
antimony, which appears of a more or less red-yellow colour, and 

* In very minute and exact experiments it is necessary further to transmit 
the gas through another connecting tube, loosely filled with cotton, in order 
to prevent it from carrying with it any moisture with which it may be charged, 
into the emission part of the tube. Vide engraving of Marsh’s apparatus for 
the reduction of arsenic, § 94 d 7. 


PROTOXIDE OF TIN. 


1 17 

jilmost black when in thick layers. If a weak stream of dry hydro- 
chloric acid gas be then transmitted through the same glass tube, the 
; ulphuret of antimony disappears, immediately, when only present 
uq thin layers, and, after a few seconds, when the incrustation is 
omewhat thicker. For sulpliuret of antimony readily decomposes 
uith hydrochloric acid gas, and the nascent chloride of antimony 
-s very volatile in the stream of hydrochloric acid gas. If 
his gas stream be transmitted through water, the presence of an- 
nnony in the latter may easily be proved by means of sulphu- 
retted hydrogen. By this combination of reactions, antimony may 
foe distinguished with certainty from all other metals. 

7. If compounds of antimony mixed with carbonate of soda, on a 
harcoal support, be exposed to the reducing blow-pipe flame, 
m kittle globules of metallic antimonv are obtained. At the 
ame time, volatilization of the reduced and reoxidized metal takes 
dace, which, even after the removal of the test specimen from the 
[lame, continues for some time, and becomes especially evident 
dhen a stream of air is directed by means of the blow-pipe 
ijpon the surface of the cooling mass. The oxide formed is partly 
I eposed on the charcoal as a white crust, and partly surrounds the 
metallic globule in the form of fine chrystalline needles. 

b. protoxide of tin. (SnO.) 

1. The protosalts of tin are colourless, and decompose when 
taeated. Tho soluble salts when neutral, redden litmus paper 
When solutions of neutral stannous salts are diluted with water, 
ihey become turbid and of a milky-white colour, owing to their 
kecomposition into soluble acid and insoluble basic salts. The 
Addition of hydrochloric acid causes the milkiness to disappear. 

2. Sulphuretted hydrogen precipitates from neutral and acid, 
ait not from alkaline solutions, dark brown sulphuret of tin, 
'Sn S,) which is soluble as well in potash and in alkaline sul- 

hurcts, especially in such as contain larger proportions of sul- 
lmr, as also in concentrated boiling hydrochloric acid. Boiling 
nitric acid converts it into insoluble peroxide of tin. 


1 1H 


PEROXIDE OE TIN. 


9. Hydrosulphuret of ammonia occasions the same precipitate 
of sulphuret of tin, which very sparingly dissolves in an ex- 
coss of the precipitant. If the hydrosulphuret of ammonia has 
already turned yellow, i. e. if it contains an excess of sulphur, or 
if finely powdered sulphur be added, the solution is much facili- 
tated. From this solution, in hydrosulphuret of ammonia, with 
excess of sulphur, acids precipitate yellow bisulphuret of tin mixed 
with sulphur. 

4. Potash, ammonia, carbonate of potash, and carbonate of 
ammonia, produce a white and bulky precipitate of hydrated pro- 
toxide of tin, (Sn O, HO,) which readily dissolves in an excess 
of potash, but is insoluble in an excess of the other three preci- 
pitants. 

5. Perchloride of gold produces in solutions of protochlorido 
or protoxide of tin, a precipitate or tinge of purple of Cassius, 
on the addition of some nitric acid, (without the application of 
heat,) vide § 93, a. G. 

0. If to a solution of protochloride or protoxide of tin, solution 
of perchloride of mercury be added in excess, a wliite precipitate of 
protochloride of mercury will be formed owing to the salt of 
tin depriving the perchloride of mercury of half its chlorine. 

7. If proto-compounds of tin be mixed with carbonate of soda 
and some borax, or better still, with equal parts of carbonate of 
soda and cyanide of potassium, and then, on a charcoal support, be 
exposed to the inner blow-pipe flame, ductile grains of metallic 
tin will be obtained, without simultaneous incrustation. They 
may be most easily detected by scraping off the specimen and the 
particles surrounding, that part of the charcoal which contained the 
specimen, strongly triturating them in a mortar, and washing the 
coal off from the metallic particles. 

c. peroxide of tin. (Sn 0 2 .) 

1 . Peroxide of tin exists in two modifications which exhibit a 
different relation to solvents. When precipitated from its salts, 
by alkalies, it is easily soluble both in potash and acids, but when 
produced by oxidation of metallic tin by means of nitre acid, 




PEROXIDE OE TIN. 


119 


is insoluble in these solvents, (the precipitated oxide of tin 
Iso becomes insoluble on being heated to redness.) The inso- 
ible modification is converted into the soluble, by fusion with 
arbonate of soda. 

2. The persalts of tin are colourless and decompose at a red 
eat. The soluble neutral persalts of tin redden litmus paper. 

3. Sulphuretted hydrogen throws down, from acid and neutral 
elutions, a yellow precipitate of bisulphuret of tin, (Sn S 2 .) 
.lkaline solutions are not precipitated. The bisulphuret of tin is 
aluble in pure alkalies, in alkaline carbonates and bicarbonates, 
l alkaline sulphurets, and in concentrated and boiling hvdro- 
hloric acid. Nitric acid converts it into insoluble peroxide of tin. 
)n deflagrating bisulpliurte of tin with nitre, sulphate of potash, 
ndstannate of potash are formed. If a solution of bisulphuret of 
n in potash be boiled with oxide of copper, sulphuret of copper 
ud peroxide of tin will be formed, which latter substance remains 
l solution in the potash. 

4. Hydrosulphuret of ammonia produces the same precipitate 
f bisulphuret of tin, which readily redissolves in an excess of 
le precipitant. Acids reprecipitate from this solution, the bi- 
llpliuret of tin in its unaltered state. 

5. Potash and ammonia, carbonate of potash, and carbonate 
f ammonia, precipitate a white hydrated peroxide of tin, 
liich readily redissolves in potash and carbonate of potash (in 
xeess,) but is sparingly soluble in ammonia, and quite insoluble 
i carbonate of ammonia. 

G. Metallic zinc precipitates, from solutions of perchloride or 
ersalts of tin, when containing no free nitric acid, metallic tin, 
i the shape of small grey leaves or as a spongy mass. If, on 
ic contrary, nitric acid be present, white peroxide or a mixture of 
letallic tin and of peroxide of tin will precipitate. 

7. I he per-compounds of tin exibit the same properties before 
ie blow-pipe as the proto-compounds. 


120 


ARSENIOUS ACID. 


( I . ARSENIOUS ACID. (As 0 3 .) 


1. Arsenious aciil on being heated volatilizes in white inodo- 
rous vapours. Its salts, on being heated to redness, generally are 
decomposed into fixed arseniates and arsenic, which volatilizes. 
Of the arsenites only those with an alkaline base are soluble. 

2. Sulphuretted hydrogen precipitates the solutions of arsenious 
acid and of neutral arsenites, slowly and incompl^cly, but when a 
free acid is present, totally and immediately ; these precipitates have 
a lively yellow colour. Alkaline solutions are not precipitated. The 
yellow precipitate of suldho-arsenious acid, (As S 3> ) is readily 
and completely redissolved in pure alkalies, in alkaline carbonates 
and bicarbonatcs, and in alkaline sulphurets, but is almost insoluble 
in hydrochloric acid. Boiling nitric acid readily decomposes and 
dissolves it. On deflagrating it with carbonate of soda and 
nitrate of potash, urseniated alkali and sulphated alkali are ob- 
tained. When a solution of sulpharsenious acid in potash is 
boiled with oxide of copper, sulphuret of copper and arseniate of 
potash are formed ; and when the same solution is boiled with 
pure oxide of bismuth, or with a carbonate or basic nitrate of the 
same substance, sulphuret of bismuth and arsenious acid are 
formed. If sulpharsenious acid be mixed with from three to 
four parts of carbonate of soda, with the addition of some water, 
and the magma be then spread over some small glass splin- 
ters, and the latter, after having been well dried, be rapidly heated 
to redness, in a glass tube, ( c . vide sketch,) through which 
dry hydrogen gas is transmitted, half of the arsenic contained in 
the mixture forms a metallic mirror within the tube. For when 
fusing two eq. of sulpharsenious acid, together with four eq. of 
soda, sulpliarsenico sulphuret of sodium and arsenite of soda are 
formed ; heating these products in hydrogen gas, all the arsenic 
is expelled, if the heat is strong and continuous. This method, 
although a great portion of the reduced arsenic is carried off, sus- 
pended in the hydrogen gas, yields nevertheless very good results. 
If the hydrogen gas be kindled at the exit aperture of the tube c, 
and a cold porcelain plate depressed on the flame, this arsenic 




ARSEN 10 US ACID. 


I 2 I 


carried away with the hydrogen gas) will condense upon the 
iblate. If a red heat be applied to another part of the tube c , 
more towards its anterior aperture, (the part first heated being at 
he same time maintained at a red heat,) another sublimate will 
oe formed beyond the heated spot, the particles of arsenic carried 
i, away with the stream of the hydrogen gas, being reconverted, at 
iLhe red hot spot, into arsenic vapours in a state of expansion, and 
[thus condensing again as a sublimate, on coming into contact 
with the cold part of the glass tube. If the heat thus simultaneously 
t ipplied to two parts of the tube be strong, whilst the stream of the 
hydrogen gas is feeble, scarcely any arsenic will be carried away 
with the gas. No arseniuretted hydrogen is formed in this opera- 
tion and those who explain the phenomena just described, by the 
formation of arseniuretted hydrogen, are in error. (Fresenius 
and Babo.) The apparatus may be constructed as in the annexed 
sketch. 


a is the evolution flask, b a tube containing chloride of calcium. 
c the tube in which, at the point d, the glass splinter with the 
•specimen is placed. This part is then (the apparatus being com- 
pletely filled with pure hydrogen gas) exposed to a slight heat, 
at first, in order to expel all moisture, and then suddenly to a 
very strong heat, (this is best done with a blow-pipe,) to prevent 
the sublimation of undecomposed sulphuret of arsenic. The 
metallic mirror is formed near the point e. 

3. Hydrosulphuret of ammonia causes also the formation of 
sulpharsenious acjd. In neutral or alkaline solutions, how- 



ARSENIOUS ACID. 


122 


ever, this substance is not precipitated, but remains in solution as 
sulpliarsenico sulphuret of ammonia. On the addition of free 
acid it precipitates immediately from this solution. 

4. Nitrate of silver produces in neutral solutions of the arse- 
nites, a yellow precipitate of arsenite of silver, (2 Ag 0, 
As O 3 ) which is soluble both in dilute nitric acid and in ammo, 
nia. Ammonio-nituate of silver yields the same precipitate with 
solutions of arsenious acid or arsenites when containing free acid. 

5. Sulphate of copper and ammonia-sulphate of copper pro- 
duce, under the same circumstances as the salts of silver, yellow 
gi*een precipitates of arsenitk of copper, (2 Cu 0, As Os.) 

0. If arsenious acid be dissolved in solution of caustic potash 
in excess, or if the solution of an alkaline arsenite bo mixed with 
caustic potash, and a few drops of a dilute solution of sulphate of 
copper be added and the mixture boiled, a red precipitate of pro- 
toxide of copper is formed, and arseniate of potash remains in 
solution. This reaction is highly sensible, provided only a 
minute cpiantity of solution of blue vitriol be used. If the red 
precipitate of protoxide of copper is no longer distinctly visible on 
the light falling through the tube in which the solution is con- 
tained, it will yet be distinctly seen on looking in at the top of the 
tube. That this reaction, though really important in individual 
cases as a confirmatory test of arsenious acid, and especially as a 
means of distinguishing arsenious acid from arsenic acid, yet 
cannot be employed as a means of directly detecting the presence 
of arsenic, is a matter of course, since grape sugar and other 
organic substances in the same manner separate protoxide of 
copper from salts of copper. 

7. If an acid or neutral solution of arsenious acid, or of an 
arsenite, bo mixed with zinc, water, and sulphuric acid, arse- 
niuretted hydrogen (As H 3 ) will be formed ; for the mode of its 
formation we refer to § 94, a 0. This property of arsenic affords 
us a most delicate test for its detection, and a highly important 
mcaus for its isolation. The operation is, under all circum- 
stances, conducted in the apparatus alluded to, § 94, a 6, of which 
we annex a sketch. 





AKSENIOUS ACID. 


1 2H 



a is the evolution flask, containing fragments of metallic zinc, 
sand water ; b a funnel tube, through which the sulphuric acid, 
and afterwards the liquor to be tested for arsenic, are poured into 
ifche flask ; c is a glass tube, loosely filled with smooth cotton, to 
■which a bent tube, d, is fitted by means of a perforated cork ; 
ithis tube is drawn out into a point, at its emission extremity, e, 
and pinched off at the top. When the evolution of hydrogen has 
poroceeded for some considerable time, so that it may safely be 
iinferred that all atmospheric air has been expelled from the 
apparatus, the gas is kindled at the emission aperture of the tube, 
Id, e. (It is advisable to envelope the flask with a piece of cloth 
: before kindling the gas, as an effectual means of preventing any 
accident, should an explosion take place.) It is absolutely 
•necessary to ascertain, first, whether the zinc and the sulphuric 
acid are quite free from arsenic. For this purpose, 1st, a porce- 
lain plate is depressed upon the flame, and, 2nd, the tube d e is 
heated to redness in the middle, the limb e being turned into a 
horizontal position for this purpose. If no incrustation be formed, 
■neither on the plate nor in the tube, the zinc and sulphuric acid 
contain no arsenic. The liquor to be tested is then introduced 
:into the flask through the funnel tube. If it contain arsenic, 
arson iuretted hydrogen will be evolved together with the hydrogen, 
imparting a bluish tint to the flame, owing to the arsenic separating 


AUSKNIOUS ACID. 


121 




at a red heat. At the same time white fumes of arsenious acid are 
observed, which condense upon cold objects. If a porcelain 
plate be now depressed upon the flame, black spots are formed 
on its surface, owing to the reduced and not yet reoxidized 
arsenic condensing on the plate. (Vide antimony, § 94, a 0.) 
Arsenic spots are of a rather blackish brown colour, and 
bright metallic lustre ; whilst those of antimony are of a deep 
black colour, and but very feebly lustrous. If the tube d e be 
heated to redness in the middle of its limb d, the arsenic will 
condense in the cold part of the tube, forming a particularly 
beautiful and distinct metallic crust, which is of a darker appear- 
ance and less silvery than that formed by antimony under similar 
circumstances ; it may moreover be clearly detected by the cha- 
racteristic odour of garlic which is perceived, if the tube is cut 
off near the incrustation, and the latter then volatilized by heat. 
The characteristic odour of alcarsin (vide 10 seq.) is even a safer 
indication than that of garlic. If the metallic spots of crust 
formed on the porcelain plate seem to indicate the presence of 
arsenic, it is still necessary to make quite sure that it is really 
arsenic and not antimony we have before us, for even the cha- 
racteristic odour of garlic or alcarsin is not sufficient to set all 
doubts at rest as to this point. The following are the best me- 
thods of ascertaining the presence of arsenic beyond doubt: — 
a, a fine and distinct metallic mirror is formed within the tube 
through which the arseniuretted hydrogen passes, on heating its 
middle part to redness. A very feeble stream of dry sulphuretted hy- 
drogen is then transmitted through this tube, with simultaneous ap- 
plication of the heat of a spirit-lamp to the metallic crust, from its 
outer towards its inner extremity. If arsenic alone be present, a 
yellow sulphuret of arsenic will be formed within the tube ; and if 
antimony alone be present, an orange or black sulphuret of anti- 
mony ; but if both metals be present, both sulphurets will be 
formed side by side, the sulphuret of arsenic, as the more volatile, 
always preceding the sulphuret of antimony. Not long ago, this 
conversion of antimony and arsenic into sulphurets was suggested 
as the surest means of distinguishing these two metals from each 





ARSENIOUS ACID. 


125 


I j tlier. Experience has, however, taught us that these differences 
n colour and volatility are not striking enough to prevent 
llie possibility of mistakes. But if dry hydrochloric acid gas be 
rransmitted through the tube containing the deposit under 
examination, without application of heat, no alteration what- 
ever will take place if sulphuret of arsenic alone is present, 
even if the gas be transmitted through the tube for a con- 
siderable time. If sulphuret of antimony alone he present, it 
will entirely vanish, and if both sulphurets be present, the sul- 
iphuret of antimony will vanish immediately, whilst the yellow 
■sulphuret of arsenic remains. If a small quantity of ammonia be 
then introduced into the tube, the sulphuret of arsenic will 
dissolve, and may thus easily be distinguished from the sulphur 
which peradvcnture may have separated. My personal experience 
has convinced me of the infallibility of these tests for the detection 
of arsenic. 

b. The limb e (vide sketch of the apparatus) is turned into an 
i horizontal position, and the gas kindled and made to burn in a 
ssmall glass receiver, having a capacity of about twelve ounces. 
This receiver is placed in a beaker glass filled with cold water, and 
constantly turned and moved, so as to prevent its becoming 
Ihot. After some time, when the oxygen in the receiver becomes 
exhausted, and the flame grows feeble, another is substi- 
; tuted for the first, and several are filled in k this manner. 
They contain, 1st, arsenious acid alone, or, 2nd, oxide of 
; antimony alone, or, 3rd, both together. If the first be the case 
i the white sublimate obtained will completely dissolve in hot 
water, and the solution may then be further tested for arsenic. 
In the second case nothing will dissolve, nor in the third, if the 
oxide of antimony is present in sufficient quantity, as this gives 
riso to the formation of arsenite of antimony. The arsenic in 
this last case may be detected by dissolving the sublimate in 
slightly dilute solution of potash, and adding sulphuretted hydro- 
gen first, and then bicarbonate of ammonia in excess. All the 
antimony will precipitate as sulphuret of antimony, whilst the 
sulphuret of arsenic remains dissolved in the excess of bicar- 


ARSEN10US ACID. 


120 

bonate of ammonia. The sulphuret of arsenic precipitates on the 
addition of hydrochloric acid to the solution, till an acid reaction 
becomes manifest. Marsh was the first who suggested the 
method of detecting arsenic by tbe production of arseniuretted 
hydrogen. 

8. If arsenious acid or an arsenite be mixed with carbonate of 
soda and charcoal , and the mixture (which must be perfectly 
dry) be then heated over a spirit-lamp to redness, in a well-dried 
glass tube, closed at one end, and drawn out into a point at the 
other, the charcoal will oxidize at tho expense of the oxygen of 
the arsenious acid, and arsenic will become liberated, which 
volatilizes and condenses above the heated part of tbe tube, form- 
ing a more or less dark brown metallic mirror of great lustre. 
This crust may be further driven on in the tube by gradually 
heating the latter to redness towards its emission aperture, and 
may thus finally be expelled, when the characteristic odour of 
arsenic (on volatilizing in the air) will afford a further proof of 
its presence. For the reduction of the free arsenious acid, a 
mere fragment of charcoal is used, instead of carbonate of soda and 
charcoal ; the arsenious acid is introduced into the drawn-out 
point of the tube, the fragment of charcoal is placed over it and 
heated to redness ; heat is then applied to the point of the tube. 
This process has the advantage over tho former of not soil- 
ing the tube which is done when operating with carbonate 
of soda and charcoal. The non-appearance of the metallic crust 
is not always a sure sign that no arsenic is present, when testing 
a supposed arsenite by means of carbonate of soda and char- 
coal, as there are several compounds of arsenious acid, especially 
of those with heavy metallic oxides, as e. g. oxide of iron, which 
do not yield metallic mirrors. 

9. If arsenites, or arsenious acid, or a sulphuret of arsenic, be 
fused together with a mixture of dry carbonate of soda and 
cyanide of potassium, all the arsenic contained in the test speci- 
men will become reduced, under all circumstances, and sometimes 
the bases also, if their properties admit of this reduction ; in this 
process the oxygen which these substances lose, converts a por- 


ARSENIOUS ACID. 


127 


ittion of the cyanide of potassium into cyanate of potash. The 
operation is conducted in the following manner: — the arsenic 
compound, which must be perfectly dry, is put into a small glass 
tube, expanded into a bulb at one end, and covered with six 
I times its quantity of the mixture of perfectly dry carbonate of 
-soda and cyanide of potassium. The quantity of the whole mass 
must not fill more than half of the bulb, or else the cyanide of 
[potassium, when in fusion, will get into the tube. The heat of a 
sspirit-lamp is then applied to the bulb, and continued, as the 
ftarsenic often requires some time for its complete sublimation. 
IThe mirrors which are obtained in this process are of exceeding 
purity. These crusts are produced from all arsenites, the bases 
of which remain either altogether unreduced, or are converted 
into such arseniurets as partly or totally lose their arsenic on the 
•simple application of heat. This method may bo especially re- 
commended on account of its simplicity, neatness, and cleanness, 
as well as for the certainty of its results, even though but minute 
quantities of arsenic be present. It is especially adapted for the 
( direct production of arsenic from sulphuret of arsenic, and is in 
| t this respect superior to all other methods suggested. The most 
j-exact results are obtained by placing the sulphuret of arsenic, 
rubbed together with twelve times its amount of a mixture con- 
i-sisting of three parts of dry carbonate of potash, and one part of 

! cyanide of potassium, into a glass tube, open at its anterior 

. 

extremity. 



The mixture is best introduced into the tube by means of a slip 
of paper, folded into the shape of a gutter. This paper contain- 
ing the mixture is inserted into the tube, and the latter then being 
'turned half way round its axis, the powder falls into it (at the 
-spot a c) without soiling any other part. The tube is then gently 
i heated in its entire length, transmitting at the same time a very 
slow stream of dry carbonic acid gas (dried by means of sulphuric 


128 


AKSKNIOUS ACID. 


acid) through it, till nil water is expelled. The spot h is then 
heated to a feeble degree of redness, when, as this point is 
attained, the mixture is heated from a towards c, by means of a 
second lamp. The arsenic condenses at d, forming a crust of 
admirable purity. In this manner the most distinct metallic 
mirrors may be obtained, from one 200th part of a grain of sul- 
pliuret of arsenic, and even less. Fresenius and Babo. 

10. If to arsenious acid (either in solid form or in solution) 
some acetic acid, and then some potash in excess, be added, the 
mixture evaporated to dryness, and the residue heated to redness 
in a tube, alcarsin (Oxide of cacodyl. C4 He As+O) will be 
formed, which is immediately detected by its characteristic and 
insupportable odour. This odour immediately changes into 
that not less characteristic of chloride of cacodyl, when the 
contents of the tube are again exposed to heat, with the addition 
of a few drops of protochloride of tin. This property affords 
us also a means of further testing the metallic crusts ob- 
tained by Marsh’s apparatus. They are for this purpose boiled 
with water containing atmospheric air, till completely dissolved ; 
acetic acid, and potash in excess, are then added to the solution, 
which is evaporated to dryness, the residue heated to redness 
in a small tube, and the further operation conducted as just now 
stated. Bunsen 1ms recently suggested this method of testing 
crusts of arsenic ; these are, however, but slowly dissolved in boil- 
ing water containing air. 

11. If arsenious acid or an arsenite be exposed on a charcoal 
support to the reducing jlamc of a blow-pipe, a higldy-charac- 
teristic odour of garlic will be perceived, especially if some car- 
bonato of soda be added to the test specimen. This odour is 
owing to the reduction and reoxidation of the arseuic, and 
enables us to detect even minute quantities of this substance. 
This test, however, cannot be implicitly relied upon. The garlic 
odour belongs neither to the vapour of arsenious acid, nor to 
those of arsenic, but probably to a lower degree of oxidation of 
the latter substance. It is always perceived on exposing arsenic 
to heat, with the free access of air. 


ARSENIC ACID. 


I2‘J 

e. ARSENIC ACID. (As 0 5 . ) 

1. Arsenic acid and the arseniates are volatile only at a very 
mgh degree of heat. Nearly all the arseniates are colourless, and 
nsoluble in water, with the exception of the alkaline arseniates. 

2. Sulphuretted hydrogen does not precipitate alkaline and 
ideutral solutions ; in acid solutions it produces a yellow precipitate 
ilf sulpharsenic acid, (As S 5 .) In dilute solutions this pre- 

ipitate is often formed after the lapse of a considerable time 
twenty-four hours). Heat promotes its separation. Thesulph- 
.rsenic acid shows the same relations as the sulpharsenious 
cid to these solvents and means of decomposition w r hich 
j/e have mentioned when treating of the latter substance. If to a 
; olution of free arsenic acid or of an arseniate, sulphurous acid is 
dded, this latter substance decomposes with the arsenic acid, 
r iving rise to the formation of arsenious acid and sulphuric acid 
ff sulphuretted hydrogen, and if needed, an acid be then added, 
111 the arsencic will immediately precipitate as sulpharsenious acid. 

3. Hydrosulphuret of ammonia in neutral and alkaline 
'blutions, converts arsenic acid into sulpharsenic acid, which 
rmains in solution as sulpharsenico-sulphuret of ammonium, 
hhis compound is decomposed on the addition of an acid, and 
iilpharsenic acid precipitates. This precipitation is more rapid 
aan that from acid solutions by means of sulphuretted hydrogen. 

is promoted by heat. 

4. Nitrate of silver produces in neutral solutions of the arse- 
nates highly characteristic reddish-brown precipitates of arse- 
r ATE of silver, (3 Ag 0, As O5 ) which is soluble both in 
lute nitric acid and in ammonia. Ammonio-nitrate of silver 
elds the same precipitate with solutions of arsenic acid or 
'Seniates. 

5. Ammonio- sulphate of copper produces, under the same 
•cumstances as the salts of silver, greenish blue precipitates of 

Useniate of corPER. (2 Cu O, As Oj. ) 

6. The arseniates present the same relations as the arsenites 

K 


1 - 8.0 


ARSENIC ACID. 


to hydrogen , to carbonate of soda, and charcoal, to cyanide of I 
potassium and before the blow-pipe. 

Recapitulation and. remarks. — The separation and safe detec- 4 
tion of the oxides belonging to the second section of the sixth 
group, and especially of oxide of tin, presents difficulties under 
certain circumstances. The protoxide of tin may be easily and 
safely detected by its reaction with perchloride of gold, even in the 4 
presence of other oxides. The separation of peroxide of tin | 
from oxide of antimony succeeds pretty well in the humid way Lyl 
means of a hot solution of bitartrate of potash, or of a solution of 
free tartaric acid ; but it succeeds only when the peroxide of tin | 
is present in the form of the modification obtained by the action •* 
of nitric acid on metallic tin. To obtain tills modification, it is f 
necessary to reduce the substanco under examination by means ? 
of zinc, if this substance is not an alloy ; in this reduction the 
presence of nitric acid must bo carefully avoided. The method 
of separating the sulphurets by means of ammonia gives rise to 
errors, as the higher degrees of sulphuration of the antimony are 
soluble in ammonia ; and even the simple sulphuret of antimony 
is not absolutely insoluble in it, when mixed with a trace of free 
sulphur, which cannot easily be avoided. The presence of per- 
oxide of tin is certain only when a ductile metallic grain of tin 
is obtained in the reducing flame ; its ductility in this case 
enables us to distinguish it from antimony. This reduction is 
very easily effected before the blow-pipe by means of a mixture 
of equal parts of cyanide of potassium and carbonate of soda; 
but care should be taken that the peroxide of tin be not mixed 
with nitre, which causes it to deflagrate, &c. Peroxide of tin 
and oxide of antimony may be detected before the blow-pipe, even 
if combined, the antimony being distinguished by its characte- 
ristic oxidation crust, and the tin by its ductility after the 
volatilization of the antimony. Inexperienced students, however, 
generally fail in this method. Antimony may moreover be detected 
by the decomposition of chloride of antimony by means of water, 
and bv the colour of its sulphuret. If the sulphuret of antimony is 


ARSENIC ACID. 


131 


nixed with a large proportion of any of the sulphur- compounds of 
nrsenic, this latter mark of detection is unsafe. In this case the mixed 
HBulphurets may be heated to redness, which causes the sulphuret of 
(Arsenic to volatilize ; and the residue may be dissolved in hydro- 
chloric acid, and this solution again tested by means of sulphu- 
retted hydrogen. 

The detection of arsenic upon the whole can by no means be 
■ aid to be difficult; but nevertheless frequent errors take place, 
-specially if we content ourselves with drawing definite conclu- 
ions from individual reactions, such as the characteristic odour 
when heated on charcoal. We must, therefore, lay it down as a 
:ule that the presence of arsenic can only he proved by a concur- 
ence of the various reactions, and especially by the formation of 
metallic arsenic. It may be pretty completely separated from tin 
iy deflagrating the sulphurets with carbonate of soda and nitre. 
The presence of tin does not, however, prevent the detection of 
rsenic. But the case is different with antimony, especially in 
testing by Marsh's method, which is now so generally followed. 
U metallic mirror obtained by Marsh’s apparatus ought, therefore, 
i-ever to be considered as a proof of the presence of arsenic, if 
iiirther tests do not give the most certain conviction that the 
metallic crust is indeed produced by arsenic. And this oonvic- 
i .on is sometimes very difficult to be obtained, when we operate 
pon very minute quantities, so that the formerly used methods 
if reduction are by far superior to Marsh's method, as far as 
r vrtainty is concerned, although it cannot be denied that they do 
ot equal it in delicacy, nor in rapidity and convenience. The 
Dimplete separation of arsenic from antimony may be effected 
yy means of bicarbonate of ammonia, the simple sulphuret of 
ntimony being insoluble in this substance, whilst sulphuret of 
rrsenic readily dissolves in it. But this method of distinction 
ields a positive and certain result only in a few eases, viz. in 
mose where we are quite sure that the simple sulphuret of anti- 
mony cannot be mixed with a higher sulphuret of antimony, nor 
iith free sulphur, whilst in all other cases it easily gives rise 
• mistakes. It is, therefore, exceedingly well adapted for the 

K 2 




ARSENIC ACID. 


testing of the products of combustion obtained by means of 
Marsh’s apparatus, (vide § 94, cl 7, b,) but it cannot be used for 
the separation of the sulphurate obtained in the usual way. And 
even less complete are those separations of antimony from arsenic 
which are founded on the relations of their sulphurets to concen- 
trated hyhrochloric acid or to caustic ammonia. The separation 
of both metals from each other does not succeed even by dis- J 
solving the sulphuret in potash, and boiling the solution with 
oxide of copper. A far more certain result may be obtained by 
deflagrating the sulphurets with carbonate of soda and nitre, J 
treating the mass obtained with water, filtering, and decomposing 
with nitric acid the basic alkaline antimoniates, which the filtrate ] 
contnins in solution to a small extent. By means of this process I 
almost all the antimony is obtained as an insoluble, and all the . 
arsenic as a soluble compound. 

The presence of antimony cannot easily give rise to any errors 
in the reduction of arsenites or arseniates, by means of carbonate 
of soda and charcoal, or cyanide of potassium and carbonate of 
soda. The reduction of sulphuret of arsenic by means of cyanide 
of potassium and carbonate of soda, in a stream of carbonic acid 
gas, does not admit even of the possibility of confounding arsenic 
with antimony, and is of all methods best adapted to yield a most 
conclusive proof of the presence of arsenic. Nitrate of silver is 
the safest test for distinguishing arsenious acid from arsenic acid, 
in their aqueous solutions. If extraneous substances be contained 
in the solution, they prevent its being directly tested for arsenious 
or arsenic acid ; in that case the solution must be completely 
precipitated by means of sulphuretted hydrogen, and the sul- 
phurets obtained dissolved in liquor of potash ; this solution must 
then be boiled with pure oxide of bismuth, or with the carbonate 
or basic nitrate of bismuth ; the liquid is then filtered off from 
the sulphuret of bismuth formed ; one part of the filtered liquid 
is tested for arsenious acid by means of sulphate of copper, ac- 
cording to the method described § 94, d 6, and the other part for 
arsenic acid, by means of nitrate of silver, after neutralization 
with nitric acid. 


RELATIONS OF THE ACIDS TO REAGENTS. 


1 33 


B. RELATIONS OF THE ACIDS TO REAGENTS. 

| § 95 . 

We divide the reagents which serve for the determination of 
::iftcids, in like manner as those used for the determination of the 
i bases into general reagents, i. e. such as indicate the group 
( to which the acid under examination belongs ; and special re- 
iagents, i. e. such as enable us to detect the individual acids. 
[The determination and limitation of the groups can hardly be 
made with the same degree of exactness with the acids as with 
the bases. 

The two principal groups into which acids are divided are that 
of inorganic and that of organic acids. No characteristic 
[distinction can, however, be selected which is applicable through 
(the entire series ; for we can neither select the ternary composi- 
tion as a distinguishing mark of organic acids, nor can we define 
organic acids to be such as require for their formation the co-opc- 
ration of the vital power, for this definition not only leaves us in 
lloubt as to a great many acids, for instance, formic acid, uric 
uicid, &c., but it is in itself altogether unscientific, since all the 
vital processes in the animal and vegetable body are in fact merely 
modified chemical processes. We shall therefore select, as the 
.•haracteristac mark by which we divide organic from inorganic 
liicids, the properties they exhibit at a liigh temperature, calling 
hose organic acids, the salts of which — (especially those with 
dkaline bases or bases of the alkaline earths) — are decomposed at 
u red heat, with separation of carbon. This mark of distinction 
las the advantage of being easily perceived, and of enabling us 
>y a very simple preliminary experiment immediately to decide 
lpou the principal group to which an acid belongs. 


INORGANIC ACIDS. 


134 


I. INORGANIC ACIDS. 

First Group. 

ACIDS WHICH ARE PRECIPITATED FROM THEIR NEUTRAL SOLU- 
TIONS BY CHLORIDE of barium : Arsenic Acid, Arsen ions Acid, 
Chromic Acid, Sulphuric Acid, Phosphoric Acid, Boracic 
Acid, Oxalic Acid, Hydrofluoric Acic, Carbonic Acid, Silicic 
Acid. 

Wo subdivide this group into four classes, as follow : 

1. Acids which are decomposed, in their acid solutions, by sul- 

phuretted hydrogen, and which we have therefore already re- 
marked upon, when treating of the bases, viz. arsenious 
ACID, ARSENIC ACID, and CHROMIC ACID. 

2. Acids which are not decomposed, in their acid solutions, by 

sulphuretted hydrogen, and the barytes compounds of which 
are insolublo in hydrochloric acid. Sulphuric acid alone 
belongs to this class. 

3. Acids which are not decomposed, in their acid solutions, by 

sulphuretted hydrogen, and the barytes compounds of which 
are dissolved by hydrochloric acid, without decomposition : 
these are phosphoric acid, boracic acid, oxalic acid, and 
hydrofluoric. (Although we intend to treat of oxalic acid 
also in the organic group, yet we must consider this acid, in 
the inorganic group too, since its salts have the property of 
being decomposed at a red heat, without real carbonization, 
and it might therefore easily he overlooked as an organic 
acid.) 

4. Acids which are not decomposed, in their acid solutions, by 

sulphuretted hydrogen, and the harytes salts of which are 
soluble in hydrochloric acid, with decomposition : car- 
bonic ACID, SILICIC ACID. 


CHROMIC ACID. 


185 


First Section of the First Group of the Inorganic Acids. 

§ 90. 

a. The arsenious acid and arsenic acid, are, as we have 
stated, decomposed by sulphuretted hydrogen, so as to separate 
heir corresponding sulphurets. On account of this property, we 
javc considered them together with the bases, as it leads to con- 
ounding them with the metallic oxides rather than with other 
acids. (Vide § 93.) 

h. chromic acid. (Cr0 3 .) 

1 . The cliromates are all red or yellow ; most of them are in- 
soluble in water. Some of them are decomposed at a red heat ; 
hose with an alkaline base are fixed, and soluble in water ; the so- 
utions of the neutral chromates are yellow, those of the acid chro- 
mates are red. These tints arc still visible in highly dilute solu- 
tions. The yellow’ colour of a neutral solution changes into red 

>n the addition of a mineral acid, owing to the formation of un 
ucid salt. 

2. Sulphuretted hydrogen reduces the chromic acid, as well when 
''free as combined in solution, so as to give rise to the formation of 
oxide of chromium, water, and sulphuric acid, with precipitation 
of sulphur. Heat promotes this decomposition. If no lree acid 
-s present, only a portion of the oxide of chromium formed is kept 
n solution by the sulphuric acid formed at the same time, and a 

greenish-gray precipitate is obtained, consisting of a mixture of 
lydrated oxide of chromium and sulphur. But if free acid is pre- 
sent, a far less considerable precipitate of pure sulphur is obtained. 
Fhe salt of oxide of chromium formed imparts a green tint to the 
iiuid, in either case. 

3. Chromic acid may be reduced to chromic oxide by means of 
many other substances, especially by sulphurous acid, or by being 
seated with hydrochloric acid, particularly on the addition of 
ilcohol, (whereupon hydrochloric ether and aldehyde escape,) or 
jy metallic zinc, or by heating with tartaric acid, oxalic acid. 


130 


SULPHURIC ACII). 


&c. All these reactions are clearly characterized by the red or 
yellow colour of the solution changing into the green tint of the 
salt of oxide of chromium. 

4. Chloride of barium produces a yellowish white precipitate 
of CHROMATE of barytes (Ba O, Cr 0 3 ) which is soluble in 
hydrochloric and in nitric acid. 

5. Nitrate of silver produces a dark purple precipitate of 
CHROMATE of silver (Ag O, Cr 0 3 ) which is soluble in nitric 
acid and in ammonia. 

6. Acetate of lead produces a yellow precipitate of chromate of 
lead (Pb O, Cr O3) which is soluble in potash, and sparingly 
soluble in dilute nitric acid. The yellow colour of this precipitate 
changes to red, on the addition of ammonia. 

7. If insoluble chromates bo fused with carbonate of soda and 
nitre, and the fused mass dissolved in water, a yellow coloured 
fluid will bo obtained, the colour of which is owing to the dis- 
solved alkaline chromate ; on the addition of an acid, this colour 
changes to red. The oxides remain either in their pure state or 
as carbonates. 

Remarks . — When testing for bases we always find the chromic 
acid as chromic oxide, sinco sulphuretted hydrogen converts the 
acid into the oxido. The colour of the solution is so characteristic, 
that a further testing for it is almost unnecessary. If we have any 
reason to suppose that chromic acid is present in a substance 
under examination, and if metallic oxides are at the same time in 
the solution, we prefer reducing the chromic acid by means of 
hydrochloric acid and alcohol, to effecting this reduction by sul- 
phuretted hydrogen. The reactions with salts of silver and of 
lead afford a safe test in aqueous solutions. 


Second Section of the First Group of the Inorganic Acids. 

§ 97. 

sulphuric acid. ( S O3. ) 

1. The sulphates are, for the most part, soluble in water; the 





SULPHURIC ACID. 


137 


i nsoluble sulphates are generally white, the soluble sulphates are 

I cor the most part colourless in their chrystalline state. The sul- 
phates of alkalies and of alkaline earths are not decomposed by a 
red heat. 

2. Chloride of barium produces in solutions of sulphuric acid 
sand sulphates, even when extremely dilute, a heavy white preci- 
pitate of sulphate of barytes (Ba 0, S0 3 ) in the form of a 
jiifine powder ; this precipitate is insoluble in hydrochloric acid nncl 
un nitric acid. 

3. Acetate of lead produces a heavy, white precipitate of sul- 
PPHATE OF lead (Pb 0, S0 3 ) which is sparingly soluble in dilute 
ji nitric acid, but completely so in hot and concentrated hydrochloric 
; acid. 

4. Those sulphates which are insoluble in water and acids, are 
converted into carbonates on being fused with alkaline carbo- 
nates, giving at the same time rise to the formation of an alkahne 
sulphate. 

5. The sulphates of alkalies and alkaline earths, may be reduced 
tto sulphurets by being exposed on charcoal to the reducing flame 
'■of the blow-pipe, either by themselves or (and with greater faci- 
Llity) mixed with carbonate of soda and charcoal. These sul- 
iphurets may be detected by the odour of sulphuretted hydrogen 
vwhich they emit upon being moistened with a few drops of an 
iiacid. If this is done on a paper which has been previously dipped 
:into a solution of lead, or on a clean silver plate, (such as a po- 
Uished coin,) a black stain of sulphuret of lead or sulphuretof silver 
ds immediately formed. 

Remarks. — Of all acids, sulphuric acid is almost the easiest to 
be detected, by its characteristic and excessively sensible reaction 
'with salts ol barytes. It is only necessary to take care not to 
■ mistake for sulphate of barytes, precipitates of chloride of barium, 
and especially of nitrate of barytes, wliich ore formed when aqueous 
I solutions of these salts are mixed with fluids containing a large 
I proportion of free hydrochloric acid or free nitric acid. It is very 
easy to distinguish these precipitates from sulphate of barytes, as 


138 


PHOSPHORIC ACID. 


they immediately disappear again, on the acid fluid being diluted 
with water. It is, however, possible to be misled by this relation 
to barytes, so as to confound sulphuric acid with hydrofluosilicic 
acid. Although we have not treated of this acid, yet we may here 
as well point out, that should any doubt exist as to the nature of 
a precipitate of barytes, this may be easily set at rest by treating 
the precipitate before the blow-pipe, with carbonate of soda and 
charcoal. (Compare § 97, 5.) 


Third Section of the First Group of the Inorganic Acids. 

§ 98. 

a. PHOSPHORIC ACID. ( P0 5 . ) 

We consider here only the tribasic phosphoric acid, since this 
and its salts alone arc most frequently employed in pharmacy, 
<fec. ; we disregard altogether the monobasic and bibasic phos- 
phoric acid. 

1 . The phosphates with a fixed base are not completely decom- 
posed by heat, but they may thereby be converted, according to 
the higher or lower degree applied, into pyrophosphates or meta- 
phospliates. Of the phosphates, only those with an alkaline base arc 
soluble in water, in their neutral state. The solutions have an 
alkaline reaction. 

2. Chloride of barium produces in aqueous solutions of neutral 
or basic phosphates, a white precipitate of phosphate of barytes 
(2BaO, P0 5 ) which is soluble in hydrochloric acid and in nitric 
acid, and sparingly soluble in muriate of ammonia. 

3. Solution of gypsum produces in neutral or alkaline solutions, 
a white precipitate of phosphate of lime (2 CaO, P0 5 ) which is 
easily soluble in acids, even in acetic acid. 

4. Chloride of magnesium or sulphate of magnesia produce in 
neutral or alkaline solutions white precipitates of phosphate of 
magnesia (2 Mg 0, P0 5> ) which are, however, perceptible only in 
rather concentrated solutions, especially on the application of heat. 
But if free ammonia or carbonate of ammonia be added to a 







PHOSPHORIC ACID. 


130 


, 3 ven highly dilute solution, n white, chrystalline and quickly sub- 
siding precipitate of basic phosphate of magnesia and am- 
nmonia (2 Mg 0, NH 4 0) (P0 5 + 2 HO +10 aq.) is formed, which 
is insoluble both in ammonia find in muriate of ammonia, but is 
of easy solution in acids, even in acetic acid. This precipitate 
often becomes risible only after the lapse of some time ; agitation 
■promotes its separation. (Vide § 86, d. 5.) 

5. Nitrate of silver throws down from the solution of the 
neutral and basic alkaline phosphates, a bright yellow precipitate 
of phosphate of silver. (3 Ag 0 P, 0 3 .) If the solution 
contained a basic phosphate, the fluid in which the precipitate is 
-suspended, manifest a neutral reaction, whilst it has an acid re- 
action if the solution contained a neutral phosphate. This is 
owing to the nitric acid receiving for 3 eq. of oxide of silver 
which it yields to the phosphoric acid, only 2 eq. of alkali and 
1 eq. of water, (for the water does not neutralize tlxe character- 
istic properties of the acid.) 

6. Acetate of lead produces in neutral and alkaline solutions 
ta white precipitate of phosphate of lead, (2 Pb 0, P 0 5 ,) 
■which is easily soluble in nitric acid, and almost insoluble in 
; acetic acid. By its behaviour before the blow-pipe this preci- 
ipitate affords us an excellent means of detecting the presence of 
I phosphoric acid. For, in the first place, it is not reduced, or at 
least., only with the greatest difficulty, on being exposed on 

(charcoal, even to the reducing flame ; and it is, in the second 
] place, distinguished inasmuch as the transparent and colourless 
jpearl which it presents in the oxidizing flame, chrystallizes on 
cooling, becomes apaque, and generally shows quite distinct dode- 
cahedrons. 

7. If to a hydrochloric solution of a phosphated alkaline earth 
, per chloride of iron be added in excess, and then ammonia till the 

solution manifest an alkaline reaction, a bulky, more or less dark, 
l reddish-brown precipitate is obtained, consisting of a mixture of 
j hydrated peroxide of iron and basic perphospiiate of iron. 

' Ammonia withdraws from it but very little of its phosphoric acid, 
whilst hydrosulphuret of ammonia completely decomposes it into 


140 


BORACIC ACID. OXALIC ACID. 


sulphuret of iron and phosphate of ammonia. If an insufficient 
quantity of percliloridc of iron is used, a white precipitate of neutral 
perpliosphate of iron is formed, which redissolves on the addition of 
ammonia in excess. 


b . BOUACIC acid. (B 0 3 .) 


1 . The aqueous solution of boracic acid reddens litmus paper, 
but it tinges turmeric paper brown. The borates are not decom- 
posed by a red heat ; only those with alkaline bases are easily 
soluble in water. The solutions are colourless, and all of them, 
even those of the acid salts manifest an alkaline reaction. 

2. Chloride of barium produces in solutions of borates, when 
not too highly dilute, a white precipitate of borate of barytes, 
(Ba O. B 03, ) which is soluble in acids and ummoniacal salts. 

3. Nitrate of silver produces in rather concentrated solutions 
of borates, a white precipitate of borate of silver, (Ag 0, 
B 0 3 ,) which is soluble in nitric acid and in ammonia. 

4. If Sulphuric acid or hydrochloric acid be added to highly 
concentrated, hot solutions of borates, the boracic acid will sepa- 
rate on cooling, in the fonn of shining chrystalline scales. 

5. If free boracic acid or a borate — (in which hitter case the 
boracic acid must be liberated by the addition of sulphuric acid) — 
be ignited with alcohol, the flame will appear of a very distinct 
yellowish-green colour, especially on stirring the mixture, 
owing to the boracic acid evaporating together with the alcohol, and 
becoming incandescent in the flame. This reaction becomes most 
sensible, if the cup containing the mixture is first heated, the 
alcohol then ignited, allowed to bum for a short time, then ex- 
tinguished and rekindled. At the first flickering of the flame 
its borders appear green in that case, even though the quantity of 
the boracic acid be so minute as to produce no perceptible colour- 
ing of the flame, when treated in the usual manner. 






c. oxalic acid. (0=C 2 03.) 


1 . All the oxalates are decomposed at a red heat, owing to the 
oxalic acid decomposing into carbonic acid and carbonic oxide. 





OXALIC AGIO. 


141 


IThose which have an alkali or au alkaline earth for their base, are 
iin tins process converted into carbonates (without separation of 
carbon, when pure) ; those with a metallic base leave the metal 
behind either in its metallic state or as an oxide, according to the 
degree of reducibility of the metallic oxide. The alkaline oxa- 
lates are soluble in water, and so are some oxalates with metallic 
1 base. 

2. Chloride of barium produces in the neutral solutions of 
oxalates, a white precipitate of oxalate of barytes, (Ba 0, 
<0 + aq.,) which is soluble in nitric acid and in hydrochloric acid, 

I but is more sparingly soluble in arumoniacal salts than borate of 
barytes. 

3. Nitrate of silver produces in neutral solutions of oxalates, a 
white precipitate of oxalate of silver (Ag 0, O,) which is solu- 
ble in nitric acid and in ammonia. 

4. Lime-water, and all the soluble salts of lime, and thus also 
solution of gypsum, produce in even highly dilute solutions of 
I free oxalic acid or of oxalates, precipitates of oxalate of lime, 
l(Ca 0, 0 + 2 aq.) in the form of a fine white powder, which readily 
i dissolve in hydrochloric acid and in nitric acid, but are almost in- 
i soluble in oxalic acid, and in acetic acid. The presence of ammo- 
niacal salts does not at all prevent the formation of these preci- 
pitates. The addition of ammonia considerably promotes the 
precipitation of the free oxalic acid, by salts of lime. 

5. If oxalic acid or an oxalate in a dry state be heated with 
concentrated sulphuric acid in excess, the latter withdraws from 
the oxalic acid its necessary constitutional water, the oxalic acid 
is decomposed into carbonic acid and carbonic oxide, and 
both these gases escape with effervescence. If the quantity operated 
upon is not too minute, the escaping carbonic oxide gas may 
be kindled ; it bums with a blue flame. If in this reaction the 
sulphuric acid assumes a dark tinge, it is a sign that the oxalic 
acid contained an admixture of some organic substance. 


HYDROFLUORIC ACID. 


uy 

( 1 . HYDROFLUORIC ACID. (H FI.) 

1 . Hydrofluoric ftcid is distinguished from all other acids by its 
property of dissolving the insoluble modification of silicic acid, as 
well as the silicates insoluble in hydrochloric acid, giving rise to 
the formation of fluoride of silicon, and of water. The hydro- 
fluoric acid decomposes in the same manner with metallic oxides, 
giving rise to the formation of fluorides and of water. The fluo- 
rides of the alkaline metals are soluble in water; those corresponding 
with the alkaline earths are either not at all or hut very sparingly 
soluble in water; floride of aluminum is easily soluble. Most of 
the fluorides corresponding with the oxides of the heavy metals 
are very sparingly soluble in water, such as, for instance, fluoride 
of copper, fluoride of lead, fluoride of zinc; many other fluorides 
are of easy solution in water, as, for instance, perfluoride of iron, 
fluoride of tin, perfluoride of mercury, &c. Of those compounds 
winch are either insoluble or but sparingly soluble in water, many 
dissolve in free hydrofluoric acid, whilst others remain undis- 
solved. Most of the fluorides do not undergo decomposition, when 
heated to redness in a crucible. 

2. If to the aqueous solution of hydrofluoric acid or of a flu- 
oride, chloride of calcium be added, fluoride of calcium, 
(Ca FI,) is obtained in the form of a gelatinous precipitate, which 
is so transparent, as at first to induce the belief, that the fluid has 
remained clear and unaltered. The addition of ammonia promotes 
the complete separation of this precipitate, which is insoluble in 
hydrochloric acid and nitric acid, as well as in alkaline fluids when 
cold; a minute quantity is however dissolved on boiling with 
hydrochloric acid. It is scarcely more soluble in tree hydrofluoric 
acid, than in water. 

3. If any fluoride, reduced to a fine powder, be mixed with 
pounded glass or sand, and the mixture be drenched in a test tube, 
with concentrated sulphuric acid and heat applied, fluosilicic 
gas (Si FI,) is evolved, giving rise to dense white fumes in the 
air when the latter contains moisture. If the gas be transmitted 
through water — (by means of a bent tube fitted to the test tube) 

7 


HYDROFLUORIC ACID. 


143 


silicic acid separates in a gelatinous form, whilst the fluid becomes 
•strongly acid, owing to the formation of hydrofluosilicic acid, 
i (Compare § 43.) 

4. If a plate of glass be covered with bees-wax, which can 
i readily be done by heating it and allowing the wax to spread 

equally over the surface, and lines be traced on it with a point, 
(which should not be too hard, a point of wood answers best,) 
i and the plate be then covered with the solution of a fluoride mixed 
with sulphuric acid, and allowed to dry, the lines exposed will be 
found, on removing the wax, to be etched upon the glass. If we 
have but very minute quantities to test, the acid solution of a 
! fluoride mixed with sulphuric acid is, at a gentle heat, evaporated 
i to dryness, in a watch glass ; after washing off the salt mass re- 
maining, the internal surface of the glass appears dimmed. 

5. If a fluoride, reduced to a fine powder, no matter whether 
soluble or insoluble, is drenched, in a platinum crucible, with con- 
centrated sulphuric acid, and the crucible, being covered with a 
glass plate, prepared as stated above, is exposed fifteen minutes or 
half-an-hour to a gentle heat, taking always care not to melt the 
wax, the exposed lines are found engraved after the removal of the 
wax. If the quantity of hydrofluoric acid evolved by means of the 
sulphuric acid was very minute, the etching frequently is not per- 
ceived, after the removal of the wax, but if the glass be breathed 
upon, the exposed lines become visible again, owing to the unequal 
capacity of condensing water, which the etched and untouched parts 
of the plate possess. 


Remarks . — The third section contains, as we have stated, phos- 
phoric acid, boracic acid, oxalic acid, and hydrofluoric acid. The 
barytes compounds of these acids, as we have seen, are dissolved 
by hydrochloric acid, without decomposition ; alkalies therefore 
precipitate them unaltered, by neutralizing the hydrochloric acid. 
The barytes compounds of arsenious acid, arsenic acid, and chromic 
acid, present the same property, and must therefore, if present, be 
removed before any conclusion, as to the presence of phosphoric 
acid, boracic acid, oxalic acid, or hydrofluoric acid, can be drawn 


144 


HYDROFLUORIC ACID. 


from tli is precipitation of a salt of barytes. But even without 
regard to this point, no great value can be placed on their re- 
action, not even for the detection of these acids, and far less for 
their separation from other acids, since the salts of barytes in 
question, and especially the borate of barytes, are not pre- 
cipitated from their hydrochloric solutions, by ammonia, if the 
quantity of free acids present is to any extent, or if any ammoni- 
acal salt in a certain quantity is present. Boracic acid may always 
be detected by the tint which it communicates to the flame of 
alcohol, if care is taken that the solution be sufficiently concen- 
trated before the addition of the alcohol, and when the substance 
under examination is a borate, that it be mixed with a sufficient 
quantity of sulphuric acid (best concentrated). If the boracic acid 
is free, it should first be combined with an alkali when evaporating 
its solution, or else a large portion of it will volatilize with the 
vapours of the water. The phosphoric acid is sufficiently charac- 
terized by the yellow silver precipitate, by the characteristic pro- 
perties of the basic phosphate of magnesia and ammonia, (espe- 
cially the insolubility of this compound in sal ammoniac,) and 
finally, by the behaviour of phosphate of lead before the blow-pipe. 
Perchloride of iron is undoubtedly the best means of decomposing 
those phosphates which have an alkaline earth for their base, after 
they have been dissolved in hydrochloric acid. Oxalic acid may 
always easily be detected by solution of gypsum, if we only keep 
in view, that the precipitate thereby formed must not disappear on 
the addition of acetic acid, (herein it is distinguished from phos- 
phoric acid,) and must readily dissolve in dilute hydrochloric acid, 
and be converted into carbonate of lime on the application of a 
red heat, (herein it differs from hydrochloric acid). The oxalates 
of the alkaline earths are completely decomposed by boiling with 
carbonate of soda. Lastly, the hydrofluoric acid cannot easily be 
confounded with other acids; since, under all circumstances, it is 
certainly detected by its property of etching glass. The most 
sensitive results are always obtained by treating solid fluorides 
with sulphuric acid. 


CARBONIC ACID. 


1 15 


Fourth Section of the First Group of Inorganic Acids. 

§ 99. 

a. CARBONIC ACID. (C 0 2 . ) 

1 . The carbonates lose a part of their carbonic acid, at a red beat. 
All carbonates of colourless oxides appear white or colourless. 

' Only those with an alkaline base are soluble in water, in their 

ii neutral state. Their solutions have a very strong alkaline re- 
i action. Further, the bi-carbonates with alkaline bases, those also 
1 winch have an alkaline earth for their base, and some with metallic 
bases, are soluble in water. 

2. The carbonates are decomposed by all free acids soluble in 
water, with the exception of hydrocyanic acid and hydrosulphuric 
acid. In this process, the carbonic acid escapes with effervescence, 
as a colourless and almost inodorous gas, which imparts a tran- 
sient reddish tint to litmus paper. It is necessary to use the 
decomposing acid in excess, especially when operating upon a 
salt with an alkaline base, since frequently no effervescence takes 
[place, when adding the acid in too small a quantity, owing to the 
I formation of acid carbonates. 

3. Lime-water and water of barytes produce, when brought 
; into contact with carbonic acid or soluble carbonates, white preci- 
jpitates of neutral carbonate of lime or barytes. When 
i testing for free carbonic acid, the reagent ought always to be em- 
iployed in excess, as the acid carbonates of the alkaline earths are 
j soluble in water. The precipitates formed dissolve in acids, with 

effervescence, and are not precipitated again by ammonia, after 
tthe complete expulsion of the carbonic acid, by boiling. 

4. Chloride of calcium and chloride of barium yield with 
neutral alkaline carbonates immediately, and with bicarbonates 
only on boiling, precipitates of carbonate of lime or of barytes. 
These reagents yield no precipitate with free carbonic acid. 

L 


1 Hi 


SILICIC ACID. 


b. SILICIC ACID. (Si 0 3 .) 

1 . Silicic acid occurs in tivo modifications, tlic ono is soluble in 
acids and water, the other is affected only by. hydrofluoric acid. 
The soluble modification is converted by heat into the insoluble. 
Tf the insoluble modification is fused with pure alkalies or alkaline 
carbonates, a basic alkaline silicate is produced, which is soluble 
in water and from which acids separato the silicic acid in its solu- 
ble modification. Tho soluble modification readily dissolves when 
boiled with solution of potash, tho insoluble modification dissolves 
only very slowly in the same menstruum. The silicates of the 
alkalies alone aro soluble in water. 

2. The solutions of the alkaline silicates are decomposed by all 
acids ; when the solutions are highly concentrated, the silicic 
acid precipitates in the form of gelatinous flakes, whilst it remains 
dissolved in more dilute solutions. If a solution of this kind, 
mixed with an acid, (hydrochloric acid or nitric acid,) is evapo- 
rated to dryness, the silicic acid is converted from its soluble into 
its insoluble modification, and remains, therefore, as a white 
gritty powder, on tho residue being treated with water. 

3. In the silicates which have an earth or a metal for their 
base, the silicic acid is also present either in its soluble or in its 
insoluble modification. The silicates with the soluble modifica- 
tion are decomposed by boiling hydrochloric or nitric acid, the 
silicic acid separating as a gelatinous hydrate, and the decom- 
posing acid combining with the base. But on silicates with the 
insoluble modification, these acids have no action ; in order to 
separate the silicic acid from its base, such silicates must be 
either treated in the humid way, with hydrofluoric acid, or fused 
with alkaline carbonates. 

4. Carbonate of soda dissolves a large proportion of silicic acid 
in the flame of the blow-pipe, forming silicate of soda as a colour- 
less glass, which remains transparent on cooling ; the carbonic 
acid escapes with effervescence. Inexperienced students often 




SECOND GROUP OF INORGANIC ACIDS. 147 

ffail in obtaining a clear glass, because they use too much carbo- 
nate of soda in proportion to the quantity of the test specimen. 

5. Phosphate of soda and ammonia leave silicic acid almost 
entirely undissolved. The silicic acid floats about as an opaque 
'.mass in the transparent glass, and may therefore be perceived 
with greater facility in the glass when red hot than after cooling. 
The silicates present the same property ; the phosphate of soda 
find am m onia withdraws their base from them, and separate silicic 
acid. The bases are dissolved, whilst the silicic acid remains un- 
lissolved. 

Recapitulation and remarks. — Carbonic acid is generally very 
. msily detected by its salts evolving an almost inodorous gas when 
; rented with acids. We transmit the gas through lime-water or 
water of barytes, when operating upon compounds which evolve 
'Other gases at the same time. Silicic acid in its soluble modi- 
fication, (into which it must always be converted first,) is detected. 
Hinder all circumstances, by supersaturating its compounds with 
Hydrochloric acid, evaporating to dryness, treating the residue 
■with water, and testing the undissolved part before the blow-pipe. 


Second Group of Inorganic Acids. 

.(iCIDS WHICH ARE PRECIPITATED BY NITRATE OF SILVER, BUT 
not by chloride of BARIUM: Hydrochloric Acid, Hydro- 
bromic Acid, Hydriodic Acid, Hydrocyanic Acid, Hydro- 
sulphuric Acid. 

§ mo. 

'V 

All the silver compounds of the oxides belonging to this group 

f ire insoluble in dilute nitric acul. The acids of this group de- 
ompose with metallic oxides, so as to give rise to the combination 
the metals with the metalloids, whilst the oxygen of the oxide 
i t the same time combines with the hydrogen of the acid forming 
Water. 


148 


HYDROCHLORIC ACID. 


O . HYDROCHLORIC ACID. (Cl H.) 

1. The chlorides are easily soluble in water, with the exception 
of chloride of lead, chloride of silver, and protochloride of mercury ; 
most of the chlorides are white or colourless. Many of them 
volatilize at a high temperature, without decomposition ; many 
chlorides are decomposed at a red heat, and hut few of them are 
fixed. 

2. Hydrochloric acid, and solutions of chlorides, yield with 
nitrate of silver, even when highly dilute, white precipitates of 
chloride of silver, (Ag Cl,) which, when exposed to light, 
cliunge first into a violet colour and then into a black ; these are 
readily soluble in ammonia, insoluble in nitric acid, and fuse 
without decomposition when heated. (Vide § 90, a 4.) 

8. Protonitrate of mercury and acetate of lead produce in 
solution, containing free hydrochloric acid or chloride, precipi- 
tates of CHLORURET OF MERCURY (Hg 2 Cl) and CHLORIDE OF LEAD 
(Pb Cl.) For the properties of these precipitates, vide § 90, b 4, 
and § 90, c 4. 

4. When chlorides are heated with manganese and sulphuric 
acid, chlorine is evolved, which is easilv detected bv its yellow- 
ish-green colour, and its odour. 

5. If a chloride he rubbed together with chromate of potash, 
and the mixture be drenched with concentrated sulphuric acid, ' 
in a tubular retort, and gentle heat applied, a deep brownish-red 
gas will be copiously evolved ; (chromate of rerciiloride of 
chromium, Cr Cl +2 Cr On ;) this gas condenses into a fluid 
of the same colour, and passes over into the receiver. If this 
chromate of percliloride of chromium is mixed with ammonia in 
excess, a yellow-coloured liquid is obtained, owing to the forma- 
tion of chromate of ammonia ; this yellow colour changes into 
a reddish yellow, on the addition of an acid, owing to the forma- 
tion of acid chromate of ammonia. 


HYDROBROMIC ACID. 


149 




b. HYDROBROMIC ACID. (Br H.) 

1. The bromides have in general a great analogy with the 
chlorides, in insolubility and in their relations when exposed to 

•iheat. 

2. Nitrate of silver produces in aqueous solution of hydro- 
Ibromic acid and bromides a yellowish-white precipitate of bromide 
of silver, (Ag Br,) which is insoluble in dilute nitric acid, 
and somewhat Sparingly soluble in ammonia. 

3. Nitric acid decomposes liydrobromic acid and the bromides, 

: with the application of heat, liberating bromine, by oxidizing the 
lhydrogen or the metal. The liberated bromine colours the solu- 
i tion yellowish-red ; but if we operate upon a bromide in a solid 

form, yellowish-red vapours of bromine gas escape, with the odour 
of chlorine ; these vapours, when present in sufficient quantity, 
(•condense in the cold part of the test-tube into small drops. 

4. Chlorine, or solution of chlorine, also liberates bromine in 
•solutions of its compounds ; the fluid assuming a yellowish-red 
ttint, if the quantity of the bromine present is not too minute. 
Hf a yellow-coloured solution of this kind be agitated with ether, 
iit becomes colourless ; all the bromine dissolves in the ether, 
which appears distinctly yellow, even though but a very minute 
iquantity of bromine be present. If the etherial solution of bro- 
imine be agitated with some solution of potash, the yellow tint 
'vanishes, and we have bromide of potassium and bromate of 
ipotasli in solution. If the solution be then evaporated, and the 
iresidue heated to redness, the bromate of potash is converted into 
Ibromide of potassium. This substance may be further tested as 
1 follows : 

5. If bromides are heated with manganese and sulphuric acid 
'yellowish-red vapours of bromine are evolved. If the 
bbromine is present only in very minute quantity, the colour of 
ibheir vapours may not be visible. The experiment, in that case, 
imust be conducted in a small retort, and the vapours passing over 


UYDIUODIC ACID. 


150 

transmitted through a long condensing glass tube into small test- 
tubes, containing some starch, for if 

0. Moist starch is brought into contact with free bromine, no 
matter whether in solution or in gaseous form, yellow bromide 
of starch is formed. The colouring does not always take place 
immediately. The reaction is rendered most delicate by closing 
the test-tube which contains the starch drenched with the fluid 
under examination, before a spirit-lamp, and then inverting it, 
so that the moist starch becomes placed above the liquid. The 
slightest trace of bromine will then, after twelve to twenty-four 
hours, impart a yellow tinge to the starch. This colour vanishes 
again on the tube being allowed to stand for a longer time. 

7. If a mixture of a bromide and of chromate of potash be 
drenched with sulphuric acid, and heat opplied, a brownish-red 
gas is evolved, just as is the case with the chlorides. But this 
gas consists of pure bromine, and the fluid passing on, therefore, 
becomes not yellow, but colourless, when supersaturated with 
ammonia. 


C . I1YDR10DIC ACID. (I H.) 

1. Tho iodides also correspond in many respects with the 
chlorides. Of those, however, which contain heavy metals, by 
far more are insoluble in water than is the case with the chlorides. 
Many iodides present characteristic tints. 

2. Nitrate of silver produces in aqueous solutions of hydriodic 
acid and of iodides, yellowish white precipitates of iodide or 
silver, (Ag I,) which blacken when exposed to light, are inso- 
luble in dilute nitric acid, and very sparingly solublo in am- 
monia. 

3. A solution of one part of sulphate of copper , and two and a 
quarter ports of sulphate of iron, precipitates from aqueous 
neutral solutions of the iodides, trotiodide of copper, (Cu 2 1,) 
in the form of a dirty-white precipitate. The addition of some 
ammonia promotes the complete precipitation of the iodine. 
Chlorides and bromides are not precipitated by this reagent. 


HYPRIODIC ACID. 


161 

4. Nitric acid decomposes the liydriodie acid and the iodides in 
tthe same manner as the bromides. Colourless solutions of 
Ihydriodic acid or of the iodides are, therefore, immediately 
coloured brownish-yellow by nitric acid, even at a low tempe- 
rrature ; and from concentrated solutions the iodine separates as a 
kblack precipitate, whilst nitric oxide gas escapes with efferves- 
cence. Solid iodides, when heated with nitric acid, evolve, besides 
itlie nitric acid gas, violet vapours of iodine, which condense on 
the colder parts of the vessel into a blackish sublimate. 

5. Chlorine, and solution of chlorine, liberate iodine from its 
combinations, hut the liberated iodine combines with these re- 
agents when they are added in excess, forming a colourless chlo- 
ride OF IODINE. 

6. If iodides arc heated with concentrated sulphuric acid , or 
with sulphuric acid and manganese, iodine becomes liberated, 
<and maybe easily detected by the violet colour of its gas. If 
concentrated sulphuric acid alone has been used, sulphurous acid 

iis evolved at the same time. If the quantity of the iodine 
[present is very minute, it can no longer be detected by the 

• colour of its gas, and we have recourse to the test with starch, as 
[follows : 

7. If to a solution of iodine or of liydriodie acid, or of an 
i iodide, (the iodine in the latter must first be liberated by means 

of niti*ic acid,) thin starch paste be added, a more or less black- 
ish-blue tint or precipitate of iodide of starch is formed, even 

• though but the most minute traces of iodine be present. When 
•solution of chlorine is employed for the liberation of the iodine, 
it ought to he added very cautiously, as, owing to the formation of 

• chloride of iodine, the blue tint does not appear, or at least 
manifests itself only after the addition of sulphuretted hydrogen, 
protochloride of tin, or some other means of reduction. Even the 
:most minute traces of iodine in dry compounds of any description, 
may he detected most safely by means of starch, in the following 
: manner. The substance under examination is drenched in a 
i retort, with concentrated nitric acid, and the retort loosely closed 
with a stopper, to which a moistened slip of paper, or, better still, 


1.02 


HYDROCYANIC ACID. 


a moistened strip of white cotton cloth, imbued with starch, is 
attached ; after a few hours this will appear blue, even though 
but the most minute trace of iodine be present 

8. The iodides present the same relation to chromate of potash 
and sulphuric acid combined, as to sulphuric acid alone. (Com- 
pare § 100, a 5.) 


d. HYDROCYANIC ACID. (Cy H.) 

1 . Those cyanides which have an alkali or alkaline earth for 
their base, are soluble in water, as liydrocyanates. They are 
easily decomposed by acids, even by carbonic acid, but are not 
decomposed by heat when the access of air is prevented. When 
fused with the oxide of lead, of copper, of antimony, of tin, and 
many other oxides, they reduce these oxides, and are converted 
into cyanates. Only a few of those cyanides which contain heavy 
metals are soluble in water ; all of them are decomposed at a 
red heat, giving rise either to the formation of cyanogen and 
metals, ns the cyanides of the noble metals, or of nitrogen gas and 
carbonates, as the cyanides of the other heavy metals. Many 
combinations of cyanogen with heavy metals are not decomposed 
by dilute oxygen acids, and with difficulty by concentrated nitric 
acid. Hydrochloric acid and sulphuretted hydrogen decompose 
most of them easily and completely. Cyanogen combines with 
several metals, (iron, manganese, cobalt, chromium,) forming 
compound radicals, in which these metals cannot be detected by 
many of the usual methods. 

2. Nitrate of silver produces, in solutions of free hydro- 
cyanic acid and of alkaline liydrocyanates, white precipitates of 
cyanide of silver, (Ag Cy,) which are easily soluble in cyanide 
of potassium, somewhat difficult of solution in ammonia, and in- 
soluble in dilute nitric acid ; these precipitates are decomposed 
at a red heat, leaving the pure metallic silver behind. 

3. If to the solution of an alkaline hydrocyanate, solution of 
sulphate of iron , which has been for some time in contact with 
the air, (magnetic oxide of iron,) is added, a precipitate or tint 




HYDROCYANIC ACID. 


153 


i of Prussian blue is formed. (Compare § b8,y' 5.) Free hydro- 
( cyanic acid, to be detected in this manner, must, therefore, first 
!be combined with an alkali. If the alkali is present in excess, 

I hydrated magnetic oxide of iron is precipitated beside the Prus- 
sian blue; in that case this latter precipitate must first be re- 
dissolved by hydrochloric acid, before the blue colour of the pre- 
cipitate can appear clearly and distinctly. 

3. If to a solution of hydrocyanic acid, potash be added in 
< excess, and then finely pounded peroxide of mercury, the latter 
•substance readily dissolves just as well as in free hydrocyanic acid. 

. As peroxide of mercury is soluble in an alkaline fluid only in 
I presence of hydrocyanic acid, it follows that by means of this 

reaction we can safely detect the presence of hydrocyanic acid. 

4. The cyanogen cannot be detected in cyanide of mercury by 
any of these methods. To detect it in this combination, we add 
hydrochloric acid and metallic iron to a solution of cyanide of 
mercury. Metallic mercury' is separated in this process, and 
hydrocyanic acid and protochloride of iron foimcd, (which latter 
substance is partly converted into perchloride of iron, on exposure 
to the air). If an alkali is then added to the fluid, Prussian blue 
is formed, the colour of which, however, becomes distinct only after 
having removed, by the addition of hydrochloric acid, the excess 
of the hydrated magnetic oxide of iron present. Cyanide of 
mercury may also be easily decomposed by sulphuretted hydrogen, 
giving rise to the formation of sulphuret of mercury and hydro- 
cyanic acid. \\ hen heated, the cyanide of mercury decomposes, 
as we have already stated, (1,) into metallic mercury and cyanogen, 
which latter substance may bo detected by its characteristic effect 
on the olfactory organs. 

5. In the ferrocyanides and ferricyanides with alkaline bases, 
the presence of these compound radicals may be easily detected, in 
the former by solution of protoxide of iron, or solution of copper, 
and in the latter by solution of peroxide of iron. Free hydro- 
cyanic acid may be obtained from these cyanides by distilling 
them with sulphuric acid. The insoluble ferrocyanides and 
ferricyanides are decomposed by being heated with caustic potash 


IIYDR08ULPHURIC ACID. 


I 6 4 


or carbonate of potash, giving rise to the formation of ferrocy- 
anide of potassium, and the separation of the metals either as 
carbonates or as pure oxides. 

C . HYDROSULPHURIC ACID. (H S.) 

Sulphuretted Hydrogen Gas. 

1. Only those sulpliurets are soluble in water which have an’ 
alkali or an alkaline earth for their base. These as well as those 
which contain metals of the fourth group, (such as iron, man- 
ganese, &c.,) are decomposed by dilute mineral acids, with evolu- 
tion of sulphuretted hydrogen gas, which may easily be detected hy 
its odour, and by its action on solution of lead. (Vide infra 2.) If 
the sulphuret is of a higher degree of sulplmration, a white precipi- 
tate of minutely divided sulphur is formed at the same time, which 
can easily be distinguished from similar precipitates by its inflam- 
mability. Part of the sulpliurets of the fifth and sixth group are 
decomposed by concentrated and boiling hydrochloric acid, with 
evolution of sulphuretted hydrogen gas, whilst others are not 
dissolved by hydrochloric acid, but by concentrated and boiling 
nitric acid. The combinations of sulphur with mercury resist both 
these acids, but dissolve readily in aqua regia. On the solution 
of sulpliurets in nitric acid, and in aqua regia, sulphuric acid is 
formed ; and in most cases, moreover, sulphur separates, which is 
easily detected by its colour and behaviour when heated. 

2. If sulphuretted hydrogen in solution, or in a gaseous form, 
is brought into contact with nitrate of silver or acetate of lead i 
black precipitates of sulphuret of silver and sulphuret of 
lead are formed. (Vide supra, § 89, a, and § 89 c.) If the odour 
of sulphuretted hydrogen is, therefore, not sufficient for its de- 
tection, these reagents will afford the surest proof of its presence. 
When the sulphuretted hydrogen is in a gaseous form, a small 
slip of paper, moistened with solution of lead, is placed in the 
air to be tested ; if sulphuretted hydrogen is present, this paper 
will become covered with a thin, brownish -black and lustrous film 
of sulphuret of lead. 


HYDROSULPHUBIC ACID. 


155 


3. Ifsulphurots are exposed to th q oxidizing flame of the blow- 
} .pipe, their sulphur bums with a blue flame, emitting at the same 
I I time the well-known odour of sulphurous acid. 

Recapitulation and remarks. — Most of the acids of the first 
group are precipitated by nitrate of silver ; but these precipitates 
will not be confounded with the silver compounds of the acids of 
the second group, as the former are soluble in dilute nitric acid, 
whilst the latter are insoluble in that fluid. The presence of hydro - 
; sulphuric acid prevents us more or less horn testing for the other 
acids of the second group ; this acid must, therefore, if present, 
first be removed previous to testing for the other acids. This 
; removal may be effected by mere boiling, if the hydrosulphurio 
; acid is free, but, if combined with an alkali, by the addition of a 

( metallic salt, which does not precipitate the other acids, or at 
; least not from acid solutions. Hydriodic and hydrocyanic acid 
may be detected even in presence of hydrochloric or hydrohromic 
acid, by the reactions with starch and magnetic oxide of iron, 
which are as characteristic as they are delicate. But the detec- 
tion of chlorine and bromine is more or less difficult in presence 
of iodine and cyanogen. These latter substances, if present, 
must therefore be removed first, before we can test for chlorine 
and bromine. The separation of cyanogen is easily effected by 
heating to redness the silver compounds of the group. Cyanide 
| of silver decomposes at a red heat, whilst chloride, bromide, and 
iodide of silver undergo no decomposition. Iodine may be 
separated from bromine and chlorine, by treating the silver 
compounds with ammonia, as the iodide of silver is almost inso- 
luble in this substance. But the separation is more perfect by 
precipitating the iodine as protiodide of copper, whilst chlorine and 
bromine remain in solution. Bromine may be detected and dis- 
tinguished from chlorine, by mixing the compound containing 
both substances with hydrochloric acid and chloride of lime, or 
with solution of chlorine, and absorbing the liberated bromine 
by ether. Chlorine may be detected when present with bromine, 
by the reaction with carbonate of potash and sulphuric acid. 




NITIUC ACID. 


1 5 () 


" a 'V- v'X 

Third Group of the inorganic Acids. 

ACIDS WHICH ARE PRECIPITATED NEITHER BY SALTS OF BARYTES 
NOR SALTS OF silver: Nitric Acid, Chloric Acid. 

§ 101 . 

a. NITRIC ACID. (N0 5 .) 

1. All the neutral salts of nitric acid arc soluble in water ; only 
a few basic nitrates are insoluble in water. All nitrates are de- 
composed at a strong red heat. Those with alkaline bases yield 
oxygen and nitrogen ; the other salts, oxygen and nitrous 
acid. 

2. If a nitrate is thrown upon red-hot charcoal, or if char- 
coal or some organic substance, paper, for instance, is brought into 
contact with a nitrate in fusion, deflagration takes place, i. e. 
the charcoal burns at the expense of the oxygen of the nitric acid, 
with vivid scintillations. 

3. If a nitrate is mixed with cyanide of potassium in powder 
and the mixture heated on a platinum plate, a vivid deflagration 
takes place combined with distinct ignition and feeble detona- 
tion. Even very minute quantities of nitrates may be detected by 
this reaction. 

4. If the solution of a nitrate be mixed with one-fourth part of 
its quantity of concentrated sulphuric acid, and a chrvstal of pro- 
tosulphate of iron be thrown into the mixture, the fluid imme- 
diately surrounding this crystal will assume a deep brown tint. 
This tint generally vanishes by merely agitating the fluid, and always 
after the application of heat for some time. In this process, the 
nitric acid is decomposed by the protoxide of iron, three-fifths of 
its oxygen combine with the protoxide, and convert a portion of it 
into peroxide, and the remaining nitric oxide combines with 
the remaining protoxide of iron, forming a characteristic com- 
pound, which dissolves in water producing a brownish -black colour. 

5. If to the solution of a nitrate some sulphuric acid be added, 
and as much solution of sulphate of indigo as to make the fluid 


CHLORIC ACID. 


157 

i appear of a feeble light blue colour, and the mixture be then 
1 heated to boiling, this blue tint will disappear, owing to the indigo 

[ becoming oxidized at the expense of the oxygen of the nitric acid 
liberated by the sulphuric acid ; the fluid becomes colourless, or 
: assumes a feeble yellowish tint. Several other substances, espe- 
i cially free chlorine, cause the same discoloration, which ought to 
; be especially borne in mind. 

1 6. If a nitrate is mixed with copper filings, and the mixture 
drenched with concentrated sulphuric acid, in a test tube, the air 
; in the tube assumes a yellowish red tint, owing to the nitric oxide 
j gas which becomes free on the oxidation of the copper by the 
; nitric acid, combining with the oxygen of the air, and forming 
nitrous acid. 


b. CHLORIC ACID. (Cl 0 5 .) 

1 . All chlorates are soluble in water. When heated to redness, 
their oxygen escapes completely, leaving chlorides behind. 

2. When heated with charcoal or some organic substance, the 
chlorates deflagrate, and this with by far greater violence 
than the nitrates. 

3. If a chlorate is mixed with cyanide of potassium, and the 
mixture heated on a platinum plate, deflagration takes place, 
with strong detonation and the appearance of flame, even though 
the chlorate be present only in a very minute quantity. 

4. Free chloric acid oxidizes and discolours indigo in the same 
manner as nitric acid ; if, therefore, the solution of a chlorate is 
mixed with sulphuric acid and solution of indigo, the phenomena 
manifest themselves which we have described when treating of 
nitric acid, (vide supra, a 5.) 

5. If cldorates be heated with hydrochloric acid, the consti- 
tuents of both acids are mutually decomposed, giving rise to the 
formation of water, chlorous acid and chlorine, which latter sub- 
stances may easily be detected by their odour and their greenish 
colour. (Cl H + Cl 0 6 = Cl 0 4 + C1 + HO.) 

6. If a chlorate be drenched with concentrated sulphuric acid, 
two-thirds of the metallic oxide are converted into a sulphate, and 


158 


CHLORIC ACID. 


the oilier third into a hyperchlorate, whilst chlorous acid escapes, 
which is characterized by its odour and greenish colour. [8 (KO, 
Cl O s ) + 2 S0 3 = 2 (KO, 2S0 3 ) + KO, CIO 7 + 2 (Cl O 4 .) ] 
The application of heat must bo avoided in this experiment, and 
small quantities only operated upon, or else the decomposition 
might take place with great violence, so as to occasion an ex- 
plosion. 

Recapitulation and remarks . — Of the reactions which have been 
suggested for the detection of nitric acid, those with sulphate of 
iron and sulphuric acid, and with copper filings and sulphuric 
acid, give the safest results, for deflagration with charcoal, detona- 
tion with cyanide of potassium, and discoloration of solution of 
indigo take place, as we have stated also when chlorates are pre- 
sent instead of nitrates. These latter reactions, therefore, are de- 
cisive only when no chloric acid is present. The best test to 
ascertain whether chloric acid bo present or not, is to heat the 
test specimen to redness, dissolving it and then testing its solu- 
tion with nitrate of silver. 

If a chlorate be present, it is converted into a chloride, on being 
heated to redness, and a precipitate of chloride of silver is ob- 
tained, on testing the solution with nitrate of silver. But this 
test is thus simple only when no chloride is present at the same 
time. But if the latter is the case, nitrate of silver must be added 
as long as any precipitate is formed ; the supernatant liquid is then 
filtered from this precipitate, evaporated to dryness, and the residue 
heated to redness. The results obtained by the fusion of chlorates 
with cyanide of potassium are less certain. The violence and de- 
tonation, with which the deflagration takes place, render it, how- 
ever, scarcely possible to confound the chlorates with nitrates. 


TARTARIC ACID. 


159 


II. ORGANIC ACIDS. 

First Group. 

ACIDS WHICH ARE PRECIPITATED BY CHLORIDE OF CALCIUM : Ox- 
alic Acid , Tartaric Acid, Paratartaric Acid, Citric Acid, 

Malic Acid. 

§ 102. 

None of these acids volatilize without decomposition. 

a. OXALIC ACID. 

For the reactions of oxalic acid we refer to § 98 c. 

1 ). TARTARIC ACID. (T = (C 8 H 4 Oio-) 

1 . The combinations of tartaric acid with alkalies, as well as 
• with those metallic oxides which are weak bases, are soluble in 
\ water. All tartrates insoluble in water are dissolved by hydro - 
i chloric acid. 

2. The tartaric acid and the tartrates carbonise when heated to 
rredness, emitting a perfectly characteristic odour. The salts 

which have an alkali or alkaline earth for their base, are in this 
[process converted into carbonates. 

3. If to a solution of tartaric acid, or to that of a tartrate, solu- 
tion of peroxide of iron, protoxide of manganese , or alumina, and 
then ammonia or potash be added, no precipitation takes place 
of peroxide of iron, protoxide of manganese or alumina, since the 
new-formed double tartrates are not decomposed by alkalies. Tar- 
taric acid prevents also the precipitation of several other oxides by 
alkalies. 

4. Free tartaric acid yields, with a salt of potash, and best with 
acetate of potash, a sparingly soluble precipitate of bitartrate of 
potash (KO, HO, T). The same precipitate is formed, if ace- 
tate of potash and free acetic acid, or bisulphate of potash, be 
added to a neutral tartrate. When using bisulphate of potash, wc 


100 


PARATARTARIC ACID. 


must be careful not to add it in excess. The acid tartrate of 
potash readily dissolves in alkalies and mineral acids , tartaric 
acid and acetic acid do not increase its solubility in water. Violent 
agitation greatly promotes the precipitation of tartar. 

5. Chloride of calcium throws down from the solutions of 
neutral tartrates, tartrate of lime as a -white precipitate. The 
presence of ammoniacal salts prevents the formation of this preci- 
pitate more or less. The precipitate of tartrate of lime dissolves | 
to a clear fluid, in cold and dilute solution of caustic potash. If 
this solution is boiled, the dissolved tartrate of lime separates in 
the form of a gelatinous precipitate. On cooling, the solution he- * 
comes clear again. 

6. Lime-water produces in solutions of neutral tartrates, or 
even in solutions of free tartaric acid, when added till an alkaline .*! 
reaction manifests itself, white precipitates of tartrate of lime 
(T, 2 Ca 0 8 aq.) which readily dissolve in tartaric acid. This * 
precipitate of tartrate of lime dissolves with the greatest facility ) 
in solution of sal ammoniac, and separates from this solution only 
after the lapse of several hours, in the form of small crystals, | 
deposited on the sides of the vessel. 

7. Solution of gypsum does not produce any precipitate in a 
solution of tartaric acid, and causes only a minute precipitate 
after the lapse of some time in the solution of a neutral tartrate. 


c. paratartaric acid, (racemic acid.) K= (C 4 H 2 Os.) 

1. The relations which paratartrates present to solvents, and 
their behaviour when heated, are very analogous to those of the 
tartrates, prevent, like the latter, the precipitation by alkalies of 
protoxide of manganese, peroxide of iron, alumina, &c. 

2. Paratartaric acid lias the same relations to salts of potash, 
as tartaric acid. The precipitate of acid paratartrate of potash is 
as difficult of solution ns tartar. 

3. Chloride of calcium precipitates from the solutions of free 
as well ns of combined paratartaric acid, paratartrate of lime, 
as n shining white powder. This precipitate is not soluble in sal 


CITRIC ACID. 


101 


ammoniac. Cold and concentrated solution of potash dissolves it 
completely, dilute solution of potash only partly ; tliis solution 
becomes turbid and gelatinous, on boiling, and clear again on 
cooling. 

4. Lime-water produces in the solutions of neutral paratartrates, 
instantaneously, white precipitates of paratartrate of lime. 

'<B. Ca 0 + 4 aq.) It yields the same precipitate with a solution 
of parntartaric acid, when added, till an alkaline reaction becomes 

! i manifest. When added in a smaller proportion, so that the solu- 
tion still remains acid, this precipitate is formed only after the 
! lapse of a few moments. Paratartrate of lime is insoluble in pa- 
, : ratartario acid as well as in tartaric acid ; when it is dissolved in 
I hydrochloric acid, and ammonia added in excess, it precipitates 
again instantaneously, or at loast after the lapse of a few mo- 
i ments. 

6. Solution of gypsum does not instantaneously produce a pre- 
icipitate in a solution of paratartaric acid ; after ten or fifteen 
miinutes, however, paratartrate of lime precipitates ; in solutions 
•of neutral paratartrates the precipitation is instantaneous. 

7. If chrystallized paratartaric acid, or a paratartrate is heated 
vwith concentrated sulphuric acid, the latter assumes a black tinge, 
cowing to tire evolution of sulphurous acid and carbonic oxide gas. 
TTartaric acid has the same property. 




d. citric acid. (Ci ~ (C 12 H On.) 

1. The citrates with alkaline bases arc easily soluble in water, 
as well in their neutral as in their acid state ; the same is the case 
with the combinations of citric acid with such of the metallic 
oxides as are weak bases. Citric acid prevents the precipitation 
of peroxide of iron, protoxide of manganese, alumina, &c., in the 

Lsame manner as tartaric acid. 

2. Citric acid and the citrates carbonize when heated to redness, 
'.emitting pungent acid vapour, which may be easily distinguished 
i by their odour from those caused by the combustion of tartaric 
uacid. 

M 


1G2 


MALIC ACID. 


3. Chloride of calcium produces no precipitate in a solution of 
citric acid, not even on boiling. But if the free acid be saturated 
with potash or soda, a precipitate of neutral citrate of lime 
(Ci, 3 CaO, 4 aq.) is formed instantaneously. This precipitate is 
insoluble in potash, but readily dissolves in solution of sal ammo- 
niac. If this solution in sal ammoniac is boiled, a white and 
heavy precipitate of basic citrate of lime (Ci, 3 Ca 0 + CaO + aq.) 
separates immediately. If a solution of citric acid, mixed with 
chloride of calcium, bo saturated with ammonia, no precipi- 
tate will be formed at a low temperature, (if the solution was 
not higlily concentrated.) But if the clear fluid be then boiled, a 
white, heavy precipitate of basic citrate of lime separates sud- 
denly. 

4. Lime-water produces no precipitate in a cold solution of 
citric acid or of a citrate. But on heating the solution to boiling 
with excess of lime-water, a white precipitate of basic citrate of 
lime is formed, which disappears again on cooling. 

6. If to a solution of citric acid, acetate of lead be added in 
excess, a white precipitate of citrate of lead (Ci, 3 Pb 0, aq.) is 
formed, which is very sparingly soluble in ammonia, but easy of 
solution in citrate of ammonia. A precipitate of citrate of lead is 
equally formed, on adding citric acid in excess to a solution of 
neutral acetate of lead. This precipitate readily redissolves on 
the addition of ammonia. We have just now seen that the citrate 
of lead is very sparingly soluble in ammonia ; tliis solution there- 
fore is not caused by the ammonia, but by the new citrate of am- 
monia. 

6. If citric acid or a citrate is heated with concentrated sul- 
phuric acid, carbonic oxide gas and carbonic acid escape first, 
without simultaneous blackening of the sulphuric acid ; but after 
boiling for some time, the solution becomes dark coloured, and sul- 
phurous acid escapes. 

e. malic acid. (M = ( C 8 H 4 0 8 . ) 

1. Malic acid forms with most bases, salts soluble in water. 
The acid malate of potash is not of difficult solution in water. 


MALIC ACID. 


1G3 


Malic acid prevents the precipitation of the peroxide of iron, &c. 
by alkalies, in the same manner as tartaric acid. 

2. When heated to 200° Reaumur, malic acid is decom- 
posed into maleic acid and HU mari c acid. This property is 
highly characteristic. If the experiment is made in a spoon, 
pungent acid vapours of maleic acid are evolved with froth, but 
if conducted in a tube, these vapours condense in the cold 
part of the tube, forming crystals. The fumaric acid remains 
behind. 

3. Chloride of calcium produces no precipitates, neither in so- 
lutions of free malic acid, nor in those of the malates. But if 

: after the addition of chloride of calcium, alcohol is added to the 
solution of a malate, malate of lime (M, 2Ca 0) immediately 
I j precipitates as a white powder. 

4. Lime-water precipitates neither the free nor the combined 
j i malic acid. 

6. Acetate of lead throws down from solutions of malic acid and 
< of malates, a white precipitate of malate of lead (M, 2Pb 0, 0 aq.) 
This precipitate is distinguished, 1st, by losing its curdiness, and 
(changing into concentrically-grouped needles, with the lustro of 
imother-o’-pearl, when the fluid is allowed to stand for some time; 

; and 2nd, by its melting point being lower than the boiling point 
of water. On heating, therefore, the fluid wherein this precipitate 
is suspended to the boiling point, the precipitate fuses and resem- 
Ibles resin which has been melted under water. 

G. On heating malic acid with concentrated sulphuric acid, the 
Hatter substances become black with evolution of sulphurous 
acid. 

Recapitulation and remarks. — Of the organic acids of this 
ggroup, the tartaric acid and paratartaric acid are sufficiently cha- 
rracterized by the sparing solubility of their acid salts of potash, 
lby the relation of their lime salts to solution of potash, and by 
ttlie characteristic odour which they emit during their combus- 
tion. Tartaric acid may be distinguished from paratartaric acid 
J ' best by means of its combination with lime, since tartrate of lime is 

M 2 


104 


MALIC ACID. 


soluble in free tartaric acid, and also in solution of sal ammoniac, 
and thus presents two properties, which arc wanting in paratartrate 
of lime. The paratortaric acid, moreover, difFcrs from tartaric acid 
in its relation to solution of gypsum. This relation to a certain 
extent assimilates paratartaiic acid to oxalic acid ; it does not, 
however, give rise to any mistake, when operating upon the 
free acids, since the precipitate which solution of gypsum produces s 
in solutions of paratartaric acid, is never formed instantaneously. 
The oxalates, moreover, are easily to be distinguished from the i 
paratartrates by the properties they exhibit when heated either by 
themselves or with sulphuric acid. Citric acid is best detected < 
by its relations to lime-water, or to chloride of calcium and am- 
monia. 

The sparing solubility of the washed citrate of lead in am- 
monia, distinguishes citric acid from tartaric and paratartaric acid. 
The other reagents which produce precipitates or other alterations 
in its solutions, such as chloride of gold, and salts of silver and 
mercury, &c., show the same or similar relations to tartaric and 
paratartaric acid, mid therefore do not afford us safe means of dis- ] 
tinguishing citric acid from the two latter substances. Malic acid 
would be sufficiently characterized by the properties which malate ■ 
of lead presents when heated under water, if this reaction were of 
greater sensibility, and if it were not prevented so easily by the 
presence of other acids. The precipitation of malate of lime by 
alcohol can only be of value for the detection of malic acid, when 
we have previously convinced ourselves of the absence of all other ' 
acids, the lime salts of which are sparingly soluble in water, and 
quite insoluble in alcohol, such, for instance, as sulphuric acid or 
boracic acid. It is, however, always necessary further to test the •' 
precipitate produced by alcohol. The heating of malic acid in a 
glass tube leads to the most certain result ; this test is, however, ' 
not applicable under all circumstances. 


SUCCINIC ACID. 


1 or. 


Second Group of the Organic Acids . 

ACIDS, WHICH ARE UNDER NO CONDITION WHATEVER PRECIPI- 
TATED BY CHLORIDE OF CALCIUM, BUT ARE PRECIPITATED 

FROM THEIR NEUTRAL SOLUTIONS BY PERCIILORIDE OF IRON : 

Succinic acid, Benzoic acid. 

§ 103. 

a. SUCCINIC ACID. S = ( C 4 H 2 0 3 .) 

1 . Pure succinic acid is inodorous, dissolves readily in water, 
and volatilizes completely when heated. The officinal acid, which 
has an empyreumatic odour, leaves a small carbonaceous residue. 
The succinates are decomposed at a red heat, with the exception 
of succinate of ammonia ; thoso which have an alkali or alkaline 
earth for their base, are converted into carbonates in this process. 
Most of the succinates are soluble in water ; succinic acid enters 
into insoluble or sparingly soluble combinations only with the 
metallic oxides which are weak bases. 

2. Perhloride of iron produces, in a solution of succinic acid, 
brownish pale red, bulky precipitate of tersuccinate of iron 
(Fe 9 On, 8S). To render this precipitation complete, the free acid 
must first be neutralized with ammonia. Persuccinate of iron 
readily dissolves in acids, and is decomposed by ammonia ; tho 
hydrated peroxide of iron separates, in this process of decomposi- 
tion, and succinic acid dissolves as succinate of ammonia. 

3. Acetate of lead yields with succinic acid a white precipitate 
of succinate of lead (Pb 0, S) which is soluble in succinic acid 
in excess, in solution of acetate of lead, and in acetic acid. 

4. Protonitrate of mercury and nitrate of silver also pre- 
cipitato the succinates ; these precipitates, however, are by no 
means characteristic. 

0 . The alkaline succinates are insoluble in alcohol, 


160 


BENZOIC ACID. 


b. benzoic acid. (13o=Bz 0 =Ci 4 II 3 0 3 .) 

1 . Pure benzoic acid appears in the form of white scales or 
needles, or merely as a chrystalline powder. It volatilizes com- 
pletely when heated. Its vapours causo a peculiar irritating sen- 
sation in the throat, and provoke coughing. The common officinal 
benzoic acid has the odour of benzoin, and on being heated, 
leaves a small carbonaceous residue. The benzoates of the alka- 
lies and alkalino earths, are converted into carbonates, by heat. 
Benzoic acid is very sparingly soluble in cold water, but of pretty 
easy solution in hot water and in alcohol. It forms wdtli most 
oxides salts soluble in water, and enters into insoluble or sparingly 
soluble combinations only with those oxides which are weak bases. 

2. Benzoic acid shows the same relation to chloride oj iron as 
succinic acid. The perbenzoate of iron, (Fc 2 , 0 3 , 3Be,) is how- 
ever by for brighter and more yellow than the succinate. Ammo- 
nia decomposes it in like manner as the succinate. When treated 
with stronger acids, the latter combine with the peroxide of iron, 
and the benzoic acid, on account of its sparing solubility, separates 
as a white precipitate. 

2. If to the solution of a benzoate a strong acid be added, the 
benzoic acid is expelled, and separates in the form of a shining 
white, sparingly soluble powder. The benzoic acid separates in 
the same manner from its soluble salts, (as already stated, 2,) if 
some stronger acid is added to these salts which forms soluble 
salts with the bases with which the benzoic acid was combined. 

Acetate of lead does not, or at least not immediately, precipitate 
the free benzoic acid nor the benzoate of ammonia, but it preci- 
pitates benzoates with fixed alkaline bases, in the form of white 
flakes. 

5. The alkaline benzoates are soluble in alcohol 

Recapitulation and remarks . — Succinic and benzoic acid are 
distinguished from all other acids by their ready volatility and 


ACETIC ACID. 


107 


their relation to perchloride of iron. They differ from each other in 
the colour of their persalts of iron, hut especially in their solubi- 
lity, succinic acid being readily soluble, whilst benzoic acid is very 
difficult of solution. Benzoic acid may, moreover, be detected by 
its irritating and cough-provoking vapours. Succinic acid is 
generally not quite pure, and may therefore also be detected by 
its odour of oil of amber. 

A separation of these acids from each other may be effected by 
decomposing their persalts of iron by ammonia, and treating the 
new-formed compounds with alcohol, after previous evaporation 
to dryness. The separation of these acids is, of course, even more 
simple, if we can combine them with alkalies in a more direct 
way. The benzoate in that case dissolves, whilst the succinate 
remains. 


Third Group of the Organic Acids. 

ACIDS WHICH ARE NOT PRECIPITATED, UNDER ANY CONDITION 
BY CHLORIDE OF CALCIUM OR PERCHLORIDE OF IRON : Acetic 
acid, Formic acid. 

§ 104. 

a. ACETIC ACID. (A=C 4 H 3 0 3 . ) 

1 . Acetic acid is completely volatilized by heat, forming vapours of 
a pungent odour, which in their concentrated state are inflammable 
and burn with a blue flame. The acetates are decomposed at a 
red heat. Among the products of their decomposition we usually 
find acetic acid, and invariably acetone. The acetates which have 
an alkali or alkaline earth for their base are converted into car- 
bonates, in this process. Many of those with a metallic base leave 
the rnetid behind in its metallic state, others as oxide. All the 
residues are carbonaceous. Almost all acetates are soluble in 
water and alcohol ; most of them readily dissolve in water, but a 
few are difficult of solution. 

2. If perchloride of iron is added to acetic acid, no alteration 

6 


168 


ACETIC ACID. 


takes place, but if the acid is previously saturated with ammonia, 
or if a neutral acetate is mixed with perchloride of iron, the solution 
assumes a deep and dark red tint, owing to the formation of per- 
acetate of iron. Ammonia precipitates all the peroxide of iron 
from such a solution. 

3. Neutral acetates (but not free acetic acid) yield with nitrate 
of silver, white clirystalline precipitates of acetate of silver, 
(Ag O, A) which are very sparingly soluble in cold water. They 
dissolve more readily in hot water, hut they separate again from 
the solution, on cooling, in the form of very fine crystals. 
Ammonia dissolves them readily ; free acetic acid does not in- 
crease their solubility in w r ater. 

4. Protonitrate of mercury produces in solutions of acetic acid, 
and even with greater facility in solutions of acetates, white scaly 
crystalline precipitates of frotacetate of mercury, (Hg 2 0, 
A,) which are sparingly soluble in water and acetic acid, at a low 
temperature, but easily soluble in an excess of the precipitant. 
Protaoetate of mercury dissolves in water on the application of 
heat, but separates again, on cooling, in the form of small crys- 
tals; it becomes partly decomposed in this process, metallic mer- 
cury separates and imparts a grey colour to the precipitate. If 
protonitrate of mercury is boiled with dilute acetic acid instead of 
water, the quantity of the metallic mercury separating is exceedingly 
minute. 

f>. If acetates ore heated with dilute sulphuric acid, acetic 
acid is evolved, which may be detected by its pungent odour. 
And if the acetates are heated with about equal weights of con- 
centrated sulphuric acid and alcohol, acetic ether is evolved ; 
the odour of this ether is highly characteristic and agreeable ; it 
becomes particularly perceptible on agitating the mixture when 
somewhat cooled down, and scarcely admits of any mistake, and 
certainly far less than the pungent odour of free acetic acid. 

6. If acetates are distilled with dilute sulphuric acid, and the 
distillate digested with oxide of lead in excoss, part of this oxide 
will be dissolved as a basic acetate of lead, which may easily be 
detected by its alkaline reaction. 








FORMIC ACID. 


100 


6 . FORMTC ACID. (Fo O 3 = C 2 H0 3 . ) 

1 . Formic acid has a characteristic pungent odour ; it volati- 
lizes completely on heating ; the vapours of the concentrated acid 
are inflammable and bum with a blue flame. The formiatcs, like 
the corresponding acetates, when heated to redness, leave either 
carbonates, or oxides, or metals behind ; with simultaneous sepa- 
ration of carbon, carburetted hydrogen, and escape of carbonic acid 
and of water. All combinations of formic acid with bases arc soluble 
in water ; alcohol does not dissolve all of them. 

2. Formic acid presents the same relation to per chloride of iron 
as acetic acid. 

3. Nitrate of .silver does not precipitate free formic acid, and 
precipitates alkaline formiates only from concentrated solution. 
The white, sparingly soluble, chrystalline precipitate of FORMIATE 
of silver (Fo 0 3 Ag O) soon assumes a deeper tint, owing to 
the separation of metallic silver. This reduction to metallic 
silver takes place, even at a low temperature, after the solution 
containing the formiate of silver has been allowed to stand for 
some time, but it follows instantaneously upon the fluid being 
heated with the precipitate. The same reduction of the oxide of 
silver ensues even if the solution of the formate was so dilute, 
that no precipitate had been formed, or if we have to operate upon 
free formic acid. In this process, the formic acid, which may 
he considered a compound of carbonic oxide and water, deprives 
the oxide of silver of its oxygen, giving rise to the formation of 
carbonic acid, which escapes, and of water; the metal is precipi- 
tated in its metallic state. 

4. Protonitrate of mercury does not produce precipitation in 
free formic acid ; but in concentrated solutions of alkaline for- 
miates it causes a white, sparingly soluble precipitate of proto- 
formiate of mercury, (Fo 0 3 Hg 2 0,) which after a very short 
time turns grey, owing to the separation of metallic mercury ; 
complete reduction takes place, sometimes even at a low tempe- 
rature. but instantaneously on heating. In this process, also. 


170 


FORMIC ACID. 


carbonic acid and water are formed. This reduction, in the same 
manner, as is the case with the nitrate of silver, takes place, even 
if the fluid is so dilute, that the protoformiate of mercury remains 
in solution, or if we have free formic acid to operate upon. 

5. If formic acid or an alkaline formiate he heated with perchlo- 
ride of mercury to 00-70° lleaumur, a precipitate of frotociiloride 
of mercury is obtained. When heated to the boiling point of 
water, metallic mercury separates besides the protochloride. 

0. If formic acid or a formiate is heated with concentrated sul- 
phuric acid, it becomes decomposed, without blackening the fluid, 
giving rise to the formation of water and carbonic oxide gas, which 
escapes with effervescence, and when ignited, burns with a blue 
flame. The sulphuric acid withdraws from the formic acid, the 
water or oxide necessary to the existence of this substance, and 
thus causes a transposition of its atoms to take place (0 2 H 0 3 = 
2 CO + HO.) If a formiate is heated with dilute nitric acid, 
formic acid escapes, which may easily be detected by its odour. 
If a formiate is drenched with a mixturo of sulphuric acid and 
alcohol, formic ether is evolved, which is characterized by its pecu- 
liar arrack smell. 

Recapitulation and remarks . — As the reactions of acetic acid 
and formic acid arc not so characteristic as those of many other 
acids, their safe detection can only be based on the concurrence of 
all the reactions we have stated. Acetic acid is most easily detected 
by its odour or by that of acotic ether, but most safely by its 
behaviour with oxide of lead. Formic acid may best be detected 
by its behaviour with sulphuric acid and with the salts of the 
noble metals. The separation of acetic acid from formic acid is 
effected by heating both acids with peroxide of mercury in excess, 
or with oxide of silver. The formic acid reduces the oxides, mid 
becomes decomposed at the same time ; the acetic acid combines 
with them and remains in solution. 


F A II T II. 


SYSTEMATIC COURSE 


OF 


QUALITATIVE CHEMICAL ANALYSIS. 





178 


PART II. 


PRELIMINARY REMARKS 


ON THE 

COURSE OF QUALITATIVE ANALYSIS IN GENERAL 

AND ON THE 

PLAN OF THIS SECOND PART OF THE PRESENT WORK 

IN PARTICULAR. 

When wo are once acquainted with the reagents and the rela- 
tion of other bodies to them, we are immediately able to determine, 
whether some simple compound or other, the physical qualities of 
which admit of drawing an inference as to its nature, is in reality 
what we take it to be. Thus, for instance, a few simple reactions 
convince us that a body which we suppose to be calcareous spar, 
is really carbonate of lime, and another substance, which we deem 
gypsum, is really sulphate of lime. This knowledge is usually 
equally sufficient to ascertain, whether a certain body be present 
or not in some compound substance or other ; for instance, 
whether a white powder contains protochloride of mercury or not. 
But if our design is to ascertain the chemical nature of a sub- 
stance entirely unknown to us, — if we wish to discover all the con- 
stituents of a mixture or a chemical combination, — if we intend to 
prove that, besides certain bodies we bavo detected in a mixture 
or compound, no other substance can be present in it, and, con- 


174 


SYSTEMATIC COURSE OF 


sequently, if a comflete qualitative analysis is our object, the 
mere knowledge of reagents and reactions is no longer sufficient ; 
wo must of necessity know besides how to proceed systematically 
in our analysis ; i. o. we must know in what order we have to 
apply solvents, and general and especial reagents, so as to be 
enabled with celerity and certainty to determine that all those 
substances which a compound or mixture does not contain, are 
really not contained in it ; and on tlio other hand, quickly and 
safely to detect those bodies which are present in the substance 
under examination. If we do not possess the knowledge of this 
systematic course, or if, in tho hope of more rapidly attaining our 
object, we adhere to no method whatever in our investigations and 
experiments, analysis becomes (at least in the hand of a novice) 
mere guessing, and the results obtained are no longer the fruits of 
scientific calculation, but mere matters of accident, which some- 
times may prove lucky hits and at others total failures. 

A definite method, therefore, must form tho basis of every 
analytical investigation. But it is not by any means necessary 
that this method should be in all cases one and tho same. Prac- 
tice, reflection, and a due attention to circumstances, will, on the 
contrary, in most cases direct us to various and different methods. 
But all analytical methods agree in this, that the substances 
existing, or supposed to exist, must first bo divided into certain 
groups, and the bodies belonging to these groups be further dis- 
tinguished from each other, so as at last to admit of their 
individual detection. The diversity of analytical methods de- 
pends partly on the order in which reagents are applied, and 
partly on their selection. 

Before we can venture upon inventing methods of our own for 
individual cases, we must first make ourselves thoroughly con- 
versant with a certain definite course or system of chemical analysis 
in general. This system must have passed through the ordeal of 
experience, and must be adapted to every case imaginable, so as 
to enable us afterwards, when we have acquired some practice in 
analysis, to determine which modification of the general method 


QUALITATIVE CHEMICAL ANALYSIS. 175 

will, in certain given cases, most easily and rapidly lead to tlie 
attainment of the object in view. 

The exposition of such a systematic course, adapted to all 
cases, tested by experience, and combining the greatest possible 
simplicity with the greatest possible security, is the object of 
the second part of this work. 

The elements and combinations comprised in it, are the same 
which we have enumerated in our preliminary remarks. 

Since it is necessary in the formation of such a systematic 
course to provide for every possible circumstance which may 
occur, it follows as a matter of course that we are obliged to 
suppose those substances which we treat of — (however mixed and 
intermixed with each other we may admit them to be) — free from 
extraneous organic matters, since the presence of such matters pre- 
vents the manifestation of many reactions, and causes various modi- 
fications in others. We by no means intend to assort here that the 
proposed systematic course may not be exactly followed even in 
presence of many organic substances, especially of those which 
dissolve in water, forming colourless transparent fluids. Expe- 
rience and reflection in every individual case will best instinct us 
how to act in cases where dark colouring slimy matters are 
present. For the most important rules, and the method in gene 
ral, we refer to § 129. 

This second part is divided into two sections ; the first contains 
practical instructions in analysis, wherein wo have pointed 
out a way which must lead to the end in view, if systematically 
followed. At first sight, many parts of it may perhaps be deemed 
rather prolix ; I think, however, that it would have scarcely been 
possible to abbreviate it, except at the expense of clearness and 
perspicuity for beginners. I hope, moreover, that my readers 
will soon become convinced by experience that this prolixity, 
after all, does not prove any bar to the celerity with which the 
systematic course may be gone through, as I have always divided 
tho phenomena which may occur, into clearly characterized in- 
stances, and thus a given object being the only one to be con- 
sidered, and one number always referring to the other, the 


170 


SYSTEMATIC COURSE, &C. 


student may save himself the trouble of reading through those parts 
which are not adapted for the especial case engaging his attention, 
J he subdivisions of this practical course are, 1, Preliminary 
examination ; 2, Solution ; 3, Real examination ; 4, Confirmatory 
experiments. The third subdivision (the real examination) is 
again subdivided into, 1, Examination of compounds in which 
we suppose but one basis and but one acid present ; and, 2, Ex- 
amination of mixtures or compounds in which we suppose that 
all those substances which we have taken into consideration may 
be present. With respect to the latter, it must be observed that 
where the preliminary examination has not afforded us the most 
certain conviction of the absence of certain groups of substances, 
we cannot safely disregard any paragraph to which we refer, in 
consequence of the phenomena that manifest themselves. In 
cases where we merely intend to test a combination or mixture for 
certain substances, and not for all its constituents, it will be easy to 
find those numbers which we have to take into consideration. 

The second section contains an explanation of the practical 
process, an exposition and explanation of the grounds whereon 
the separation, and the causes, whereon the detection of substances 
depend ; and, moreover, various additions to the first section. 
Students would do well to make themselves early acquainted with 
this section, which may be advantageously studied, concurrently 
with the practical process. 

As an appendix, w r e give a general scheme of the order in 
WHICH THOSE SUBSTANCES WHICH ARE TO BE ANALYZED FOR THE 
SAKE OF PRACTICE MAY MOST JUDICIOUSLY BE SUCCESSIVELY 
TAKEN ; and ALSO A TABULAR ARRANGEMENT OF THE MORE FRE- 
QUENTLY OCCURRING FORMS AND COMBINATIONS OF THE SUB- 
STANCES ENUMERATED IN OUR PRELIMINARY REMARKS, ACCORD- 
ING TO THEIR VARIOUS DEGREES OF SOLUBILITY IN WATER AND 
acids. The first is intended to serve the pupil as a guide to the 
rapid and certain attainment of his object; i. e. a sound and 
complete acquisition of qualitative analysis ; and the second will 
undoubtedly prove useful to many who are not yet quite conver- 
sant with the various degrees of solubility of compound bodies, 


PRELIMINARY EXAMINATION. 


177 


especially in cases where they have to draw conclusions ns to how 
the detected acids, bases, &c., have been combined, or what par- 
ticular acids cannot possibly be present in aqueous or acid solu- 
tions, when the latter contain certain bases. 


FIRST SECTION. 

PRACTICAL PROCESS. 

I. PRELIMINARY EXAMINATION. 

§ 105 . 

In the first place, the external and sensible properties of the sub- 
stance under examination should be considered, such as its colour, 
shape, hardness, gravity, odour, &c., as many conclusions may 
often be drawn therefrom. Before proceeding any further, we 
ought to consider well how much of the substance to be examined 
we have at command, since it is necessary at this early period of 
the examination to determine the quantity which we may use in 
the preliminary investigation. A reasonable economy is in all 
cases advisable, though we may possess the substance in large 
quantities ; and it must bo laid down as a fixed rule, never to 
use at once all we possess of a substance, but always to keep at 
least a small portion of it for unforeseen accidents, and for con- 
firmatory experiments. 

A. THE BODY UNDER EXAMINATION IS SOLID. 

1. IT IS NEITHER A PURE METAL NOR AN ALLOY. 

1. The substance is fit for examination when in powder or in 
small crystals ; but when in larger crystals or in solid pieces, a 
portion of it, if possible, must first be reduced to powder. 


178 


PRELIMINARY EXAMINATION 


i 


2. Tho powder is heated over the spirit-lamp, in a small iron 
spoon. Tho phenomena resulting admit of many safo inferences 
as to tho nature of the substance, and allow us to draw many 
probable conclusions. 

a. The sudstance remains unaltered : no organic 
substances, no salts containing water of crystallization, no 
easily fusible matter, no volatile bodies. 

b. It fuses easily, and becomes solid again with the 
E xruLSiON of aqueous vapour ; salts which contain water 
of crystallization. If tho solidified residue fuses again upon 
the application of an increased heat, c must be re- 
ferred to. 

c. It fuses without expulsion of aqueous vapour. A 
small piece of paper is added to the melting mass ; if defla- 
gration takes place, it indicates nitrates, or more rarely, 
CHLORATES. 

d. It volatilizes completely or partly. In the first 
case, no fixed bases are present ; in the latter, tho substance 
contains a volatilo body in admixture. 

a. No odour is emitted. In this case we must espe- 
cially have regard to compounds of ammonia, mercury, 
and arsenic. 

/3. An odour is emitted at tho same time. If it is that 
of sulphurous acid, sulphur is present ; if that of iodine, 
and if the vapours are violet, the presence of free iodine | 
is certain. With equal certainty free benzoic acid, and 
many other substances, may be detected by the odour of 
their vapours. 

e. The substance is a white towder, turning to 
yellow on heating ; this indicates OXIDE of zinc or OXIDE 
of lead ; the latter substance remains yellow on cooling, 
whilst the oxide of zinc resumes its whito colour. 

f. Carbonization takes place : organic substances. If 
the residue effervesces when drenched with acids, whilst the 
original substance does not present that property, it indi- 
cates the presence of organic acids, combined with alkalies i 


BY HEAT. THE BLOW-PIPE. 


1 71) 


or alkaline matter. If the odour of cyanogen is perceptible, 
it indicates the presence of a cyanide. 

Many substances, moreover, swell up considerably, as 
for instance, borax, sulphate of alumina ; others decrepitate, 
e. g. chloride of sodium, and chloride of potassium, &c. ; 
these phenomena, however, less admit of general and cer- 
tain conclusions than those stated above. 

3. A small portion of the substance is put on a charcoal sup- 
port, and exposed to the reducing flame of the blow-pipe. Since 
most of the phenomena just now described (2) are equally ob- 
tained by this process, we will here mention only those which 
particularly belong to the latter. 

a. The substance volatilizes partly or completely. 
This indicates besides the substances mentioned in § 105, 
2, d, also oxide of antimony, and several other oxides. 
(Compare § 105, 0, d, fi.) Oxide of antimony fuses pre- 
vious to its volatilization in the form of a white vapour, 
It must moreover bo remarked, that when arsenious or ar- 
senic acid are present, a characteristic odour of garlic is 
perceptible, which is stronger if soda lias previously been 
added to the test specimen. 

b. The body fuses, and is imbibed by the charcoal ; 
this indicates the presence of alkalies. This process is 
conducted by putting a portion of the substance reduced to 
powder on the moistened loop of a platinum wire, and apply- 
ing the heat of the reducing blow-pipo flame to it. If the 
oxidizing flame assumes a violet tint, it indicates the pre- 
sence of potash alone ; if a yellow tint, the presence of 
soda, which may, however, be mixed with potash, even in a 
considerable proportion, since the flamo always appears 
yellow when both these alkalies are present. 

c. An infusible white residue remains on the char- 
coal, EITHER IMMEDIATELY, OR AFTER PREVIOUS MELTING 
in THE WATER of crystallization ; this indicates espe- 
cially the presence of barytes, strontian, lime, magnesia, alu- 
mina, zinc, and silicic acid. Of these substances strontian, 

N 2 


180 


PRELIMINARY EXAMINATION 


lime, magnesia, and zinc, arc distinguished by being very 
luminous in the blow-pipe flame. A drop of solution of 
nitrate of cobalt is added to the white residue, and the bitter 
then again strongly heated. Alumina presents a fine blue 
tint, magnesia a reddish, and ztnc a green colour. When 
silicic acid is present, the flame assumes also a feeble 
bluish tint, which should not be confounded with that pro- 
duced by alumina. Silicic acid is moreover distinguished by 
forming a clear glass, with effervescence, when mixed with 
carbonate of soda, and exposed to a strong blow-pipe flame. 
(§ 99, b.) 

d. An infusible residue of a different colour re- 
mains, OR A METALLIC REDUCTION TAKES PLACE, WITH OR 
WITHOUT INCRUSTATION OF TIIE CHARCOAL SUPPORT. A 
portion of the powder is mixed with carbonate of soda, and 
heated in the reducing flame on charcoal. 

a. A metallic grain is obtained, without simultaneous 
incrustation of the charcoal ; this indicates the presence 
of gold, silver, tin, or copper. Platinum, iron, cobalt, 
and nickel, equally become reduced, but yield no metallic 
grains. 

/3. The charcoal support is coated over with an incrus- 
tation, either with or without simultaneous formation of a 
metallic gniin ; this indicates the presence of bismuth, 
lead, cadmium, antimony, or zinc. 

aa. If the incrustation is white, antimony or zinc 
may be supposed present. The incrustation produced 
by zinc appears yellow as long as it remains hot. The 
pure metallic grain of antimony evolves white vapour, 
even for a long time after all application of heat has 
been withdrawn ; and at last, on cooling, becomes gene- 
rally surrounded with crystals of oxide of antimony. It 
is brittle under the stroke of a hammer. 

bb. The incrustation is more or less yellow or brown ; 
this indicates the presence of bismuth, lead, or cad- 
mium. The yellow incrustation of oxide of cadmium 


OF METALS AND ALLOYS. 


181 


lias a shade of orange colour in it ; the brownish-yellow 
incrustations of oxide of lead and oxides of bismuth 
change into a light yellow on cooling. Cadmium im- 
mediately volatilizes on becoming reduced. The grains 
of lead are very ductile, wliilst the grains of bismuth are 
brittle under the stroke of the hammer. 

The student must be prepared, of course, to meet with combi- 
nations of bodies giving rise to mixed phenomena, and must 
deduce his conclusions accordingly, since we cannot give strictly 
defined cases in these general rules. 


II. THE SUBSTANCE IS A METAL OR AN ALLOY. 

1. The test-specimen is drenched and heated with water, mixed 
with some acetic acid. 

a . Hydrogen is evolved ; this indicates the presence of 
a light metal. The presence of alkalies and of alkaline 
earths must be had regard to in the real examination. 

b. No hydrogen is evolved ; this indicates the absence 
of light metals. Alkalies and alkaline earths need not bo 
considered in the course of the special investigation. 

2. The test-specimen is heated on charcoal, in the reducing 
blow-pipe flame, and the phenomena observed, such as, for in- 
stance, whether the substance fuses, whether an incrustation is 
formed, whether any odour is emitted, &c. 

a . The substance remains unaltered; this is pretty 
conclusive of the absence of antimony, zinc, lead, bismuth, 
cadmium, tin, mercury, and arsenic ; the absence of gold, 
silver, and copper, is also probable ; it indicates the presence 
of PLATINUM, IRON, MANGANESE, NICKEL, or COBALT. 

b . The substance fuses without simultaneous in- 
crustation, and without emission of odour ; this indi- 
cates the absence of antimony, zinc, lead, bismuth, cadmium, 
and arsenic, and the presence of gold, silver, copper, or 

TIN. 


182 


PRELIMINARY EXAMINATION. 


c. Tiie substance fuses wiTn tiie formation of a 

CRUST, BUT WITHOUT EMITTING ANY ODOUR ; this indicates 
the nbsence of arsenic, and the presence of antimony, zinc, 
bismuth, lead, or cadmium. (Compare § 105 A. I., 
3 d, (3.) 

d. The substance emits a garlic odour ; this indicates 
the presence of arsenic. For the other phenomena which 
may manifest themselves, we refer to a, l, or c. 

3. The suhstanco is heated before the blow-pipe in a glass tube, 
closed at ono end. 

a. No SUBLIMATE IS FORMED IN THE COLDER PART OF 
THE tube ; this indicates the absence of mercury. 

b. A sublimate is formed; this indicates the presence 
mercury, CADMIUM, or arsenic. The sublimate of mercury, 
which consists of small globules, cannot bo confounded with 
the sublimate of cadmium or arsenic. 

B. TnE SUBSTANCE UNDER EXAMINATION IS A FLUID. 

1. A small portion of the fluid is evaporated in a platinum 
spoon, or in a small porcelain crucible, to enable us to determine 
whether the fluid contains any substance in solution, and what is 
the nature of the residue. (§ 105 A.) 

2. The fluid is tested by litmus papers. 

a. Blue litmus paper becomes red. This reaction 
may bo caused either by a free acid, or an acid salt, or by a 
soluble metallic salt. In order to distinguish these two 
cases from each other, a small quantity of the liquid is 
poured into a watch-glass, and a little rod placed into it, the 
extreme point of which has previously been dipped into dilute 
solution of carbonate of potash; if the fluid remains clear, or if 
the precipitate which may form is redissolved on stirring the 
liquid, it indicates the presence of a free acid or an acid 
salt ; but if the fluid becomes turbid, it proves the presence 
of a soluble metallic salt, at least generally. As a matter of 
course, with the presence of a free acid or acid salt, the 


CLASSIFICATION OF SUBSTANCES. 


183 


solution cnnnot be considered as a mere aqueous one, and 
consequently we must look carefully to all those phenomena 
which may indicate the presence of bodies insoluble in water, 
and soluble only in acids. 

b. Reddened litmus paper becomes blue ; this indi- 
cates the presence of free alkalies, or alkaline carbonates, 
free alkaline earths, or alkaline sulphurets, and also of n 
series of other salts of which this reaction is characteristic. 
With the presence of a free alkali, a body dissolved in the 
fluid may as well belong to those soluble as to those inso- 
luble in water. We refer to § 114 I., 2, for further informa- 
tion on this subject. 

3. We test by smelling and tasting, or should this not yield 
any safe results, hy distillation, whether the simple solvent present 
is water, alcohol, ether, &c. If it is found not to be water, the 
solution is evaporated to dryness, and the residue treated accord- 
ing to § 100 A. 

4. If the solution is aqueous, and manifests an acid reaction, a 
portion of it is highly diluted with water. If it becomes milkv, 
the presence of antimony, bismuth, or tin, may be supposed. 
If the precipitate disappears on the addition of tartaric acid, we 
may conclude that antimony is present, whilst its disappearance 
on the addition of acetic acid, but not of tartaric acid, indicates 
the presence of bismuth. The original fluid is then treated either 
as § 107 directs, or § 114, according to whether we have reason 
to suppose it to bo the solution of a simple or of a compound or 
mixed substance. 

II. SOLUTION OF BODIES OR CLASSIFICATION OF SUBSTANCES AC- 
CORDING TO TIIEIR RELATIONS TO CERTAIN SOLVENTS. 

§ 10G. 

Water and hydrochloric acid, or in certain cases acetic acid, 
are the solvents used to classify simple or compound substances, 
and to isolate the component parts of mixtures. We divide sub- 
stances into three classes, according to their relations to these 
solvents. 


164 


CLASSIFICATION OF SUBSTANCES. 


First class. — Substances soluble in water. 

Second class. — Substances insoluble or sparingly 
soluble in water, but soluble in hydrochloric or 
nitric acid. 

Third class— Substances insoluble or sparingly solu- 
ble, both in water, and also in hydrochloric or 
IN nitric acid. 

A special method for the solution of alloys is given in § 100 B, 
as it is advisable to dissolve them in a manner somewhat different 
from that employed for other bodies. 

The process of solution or separation is conducted in the follow- 
ing manner. 

A. THE SUBSTANCE UNDER EXAMINATION IS NEITHER A METAL 

NOR AN ALLOY. 

1. About fifteen or twenty grains of the substance to he ex- 
amined, reduced to powder, are covered in a test-tube with ten or 
twelve times as much water, and heated to the boiling point over 
a spirit-lamp. 

a . The substance is completely dissolved. In this 
case it belongs to the first class ; regard must he had to what 
wo have stated in § 105 B, 2, concerning reactions. The 
solution is treated either as stated at § 107, and at § 114, 
according as to whether one or several acids and bases are 
supposed to be present. 

b. A RESIDUE REMAINS, EVEN AFTER BOILING THE SOLU- 
TION for A long time. The solution is allowed to settle, 
and filtered, so that the residue remains in the test-tube if 
possible ; a few chops of the clear filtrate are then evaporated 
on a clean platinum plate ; if no residue remains, the sub- 
stance is completely insoluble in water, and is then further 
tested, as stated in § 10G, 2. But if a residue remains, the 
substance is at least partly soluble. It is then again boiled 
with water, filtered, and the filtrate added to the original 
solution. This fluid is treated, according to circumstances. 


SOLUTION AND SEPARATION. 


185 


either ns § 107 directs, or ns stated § 114. The residue is 
washed, and treated according to § 100, 2. 

2. This residue is drenched with dilute hydrochloric acid. If 
it does not dissolve, it is heated to the boiling point, and if even 
then no complete solution takes place, the fluid is decanted, and 
the residue boiled with concentrated hydrochloric acid. 

The phenomena which may manifest themselves in this 
operation, and which ought to be carefully observed, are, a, 
Effervescence, which indicates the presence of carbonic acid, 
or sulphuretted hydrogen, vide § 108, 2. ft. Evolution of 
chlorine, which indicates the presence of hyperoxides, chro- 
mates, &c. y. Emission of the odour of hydrocyanic acid, 
which indicates the presence of insoluble cyanides. Since it 
is advisable to decompose the hitter in a different manner, a 
special paragraph will be devoted to them. (Vide § 128.) 

a. The residue is completely dissolved by the hy- 
drochloric acid ; the solution is treated according to cir- 
cumstances, either as directed § 110, or as stated § 114. 
The substance belongs to the second class. 

The separation of undissolved sulphur, which is easily 
detected by its colour and specific gravity, belong also to 
this category. 

b. A residue REMAINS. In this case the test-tube con- 
taining the specimen boiled with hydrochloric acid, is put 
aside pro tempore, and another specimen of the substance 
under examination is boiled with nitric acid, with the subse- 
quent addition of water. 

a. The specimen is completely dissolved , or undissolved 
sulphur alone remains; the body in these cases also 
belongs to the second class ; the solution is further tested 
for bases, according to circumstances, either as directed 
§ 110, or as stated § 114, iii. 
ft. A residue remains. 

aa. We have reason to suppose that the sub- 
stance UNDER EXAMINATION CONTAINS BUT ONE BASE 


18G 


EXAMINATION OF METALS AN1) ALLOYS. 


and one acid. Tlio substance is drenched with aqua 
regia, and then heated. 

aa. The substance dissolves. The solution is treated 
according to § 110. 

/3/3. The substance does not dissolve. In that case wo 
proceed according to § 113. 

bb. We have reason to suppose that tiie substance 

UNDER EXAMINATION IS A COMBINATION OR MIXTURE OF 
several compounds. In this case tho reserved hydro- 
clilorio solution (§ 100 A. 2, b.) is used to test for tho 
bases. It is for this purpose heated to boiling with tho 
insoluble residue — (which latter must then he treated as 
stated, § 100, 3) — and filtered hot into a tube containing 
some water, the residue is then boiled with some water, fil- 
tered hot, and the filtrate added to the hydrochloric solution. 

an. The filtrate becomes turbid and milky ; this indi- 
cates antimony or bismuth ; or it deposits fine crys- 
tals ; this indicates the presence of lead. The filtrate 
is heated again (if needed, with the addition of some 
hydrochloric acid) till it appeal's clear, and then treated, 
according to § 114, II. 

/3/3. The Jilt rate remains clear. A few r drops of it arc 
evaporated to satisfy ourselves whether the hydrochloric 
acid has dissolved anything. If any residue remains, 
the filtrate is treated according to § 114, II. 

3. If boiling concentrated hydrochloric acid has left a residue, it 
is washed with water, and treated as directed, § 127. 

B. the substance under examination is a metal or an 

ALLOY. 

The metals are best divided according to their behaviour with 
nitrio acid. 

I. Metals which are not affected by nitric acid : gold, 
platinum. 


DIVISION OF METALS. 


187 


II. Metals which are oxidized by nitric acid, but the 

OXIDES OF WHICH DO NOT DISSOLVE IN AN EXCESS OF THE ACID: 
antimony, tin. 

III. Metals which are oxidized by nitric acid, and the 

OXIDES OF WHICH DISSOLVE IN AN EXCESS OF THE ACID, FORM- 
ING nitrates : nil other metals. 

A specimen of the substance is drenched with nitric acid of 1'25 
sp. gr., and heated. 

1. CoMFLETE SOLUTION TAKES PLACE, OR IS EFFECTED BY 
the addition of water ; this indicates the absence of platinum, 
gold, antimony, and tin : a small specimen of the solution is di- 
luted with much water. 

a. The solution remains clear ; some hydrochloric acid 
is added ; if this produces a white precipitate, which does 
not dissolve, on heating the fluid, but is dissolved by am- 
monia, after having been rinsed previously, silver is present. 
The original solution is treated, as directed § 115. 

b. The solution becomes turbid and milky ; this indicates 
the presence of bismuth. The solution is filtered, and the 
filtrate tested for silver, as stated, § 106, B, 1, a. The ori- 
ginal solution is treated according to § 115. 

2. A RESIDUE REMAINS. 

a. A metallic residue remains. The solution is fil- 
tered, and the filtrate treated as directed § 106, B, 1, after 
having examined whether anything has been dissolved. The 
residue is by rinsing freed from all dissolved metallic 
particles, dissolved in aqua regio, and divided into two 
portions ; chlorido of potassium is added to one portion : 
if a yellow precipitate is formed, it indicates the pre- 
sence of platinum. Protosulphate of iron is added to the 
other portion : if a black precipitate is formed, it indicates 
the presence of gold. 

b. A white pulverulent residue remains; this indicates 
the presence of antimony or tin. The solution is filtered, 
and the filtrate treated as directed § 106, B, 1, after having 


188 


SUBSTANCES SOLUBLE IN WATER. 


examined whether anything has been dissolved. The re- 
sidue is eiu-cfully rinsed, and heated with a hot saturated 
solution of bitartrate of potash, or a solution of tartaric 
acid. 

«. Complete solution takes place ; this indicates the 
presence of oxide of antimony alone ; the solution is 
tested with solution of sulphuretted hydrogen. 

/>. A white precipitate remains, even after boiling with 
a fresh portion of solution of bitartrate of potash or of tar- 
taric acid ; this indicates the probable presence of tin. The 
solution is iiltercd and mixed with solution of sulphuretted 
hydrogen If an orange-red precipitate is formed, oxide 
of antimony is present. The presence of oxide of tin is 
ascertained by mixing the residue with cyanide of potas- 
sium and carbonate of soda, and reducing it before the 
blow-pipo. (Compare § 94, c, 7.) 


III. REAL EXAMINATION. 

Compounds supposed to consist simply of one base and one acid ; 
or one metal and one metalloid. 

A. Substances soluble in water. 

Detection of the base.* 

§ 107. 

1. Some hydrochloric acid is added to a portion of the aqueous 
solution. 

a. No precipitate is formed; this indicates the absence 
of silver and protoxide of mercury with certainty, and is also 
a probable indication of the absence of lead. For further ex- 
amination, vide § 107, 2. 

b. A precipitate is formed. Divide the fluid, in which 

* We include here arsenious and arsenic acid. 


SUBSTANCES SOLUBLE IN WATER. 


180 


the precipitate is suspended, into two portions, and add am- 
monia in excess to the one. 

a. The precipitate vanishes, and the Jluid becomes 
clear ; the precipitate in this case consists of chloride of 
silver, and is therefore indicative of the presence of silver. 
To obtain a conviction on this point, the original solution 
must he tested with chromate of potash, and with sulphu- 
retted hydrogen. (Vide § 90, a, 2, and 90, b, 5.) 

ft. The precipitate becomes black ; it consists in this 
case of protocliloride of mercury, which has been converted 
by the ammonia into protoxide of mercury, and is conse- 
quently indicative of the presence of protoxide of mer- 
cury. To set all doubt at rest as to this point, test the 
original solution with protocliloride of tin and with metallic 
copper. (Vide § 90, b.) 

y. The precipitate remains unaltered; it consists in 
this case of chloride of lead, which is neither decomposed 
nor dissolved by ammouia ; this reaction is therefore in- 
dicative of the presence of lead. We assure ourselves of 
the presence of this substance; 1st, by diluting the second 
portion of the fluid in which the precipitate produced by 
hydrochloric acid is suspended, with much water and ap- 
plying heat. The precipitate must dissolve if it really is 
chloride of lead ; 2nd, by adding dilute sulphuric acid to 
the original solution, (§ 90, c .) 

2. Solution of sulphuretted hydrogen is added to the fluid aci- 
dified with hydrochloric acid, till it has imparted its characteristic 
odour to this fluid, which the hitter must still retain even after 
stirring and shaking ; the liquid is then heated. 

a. Ihe fluid remains clear. Pass over to 3 , for lend, 
bismuth, copper, cadmium, peroxide of mercury, gold, plati- 
num, tin, antimony, arsenic, and peroxide of iron, are not 
present. 

b. A precipitate is formed. 

a. This precipitate is white; it is in this case 
produced by the separation of sulphur, and is indicative of 


190 


SUBSTANCES SOLUBLE IN WATER. 


tlio presence of peroxide of iron. (§ 88, /.) The ori- 
ginal solution is then further tested with ammonia and with 
ferrocyanide of potassium, in order to ascertain whether 
the substance present is really peroxide of iron. 

( 1 . The precipitate is yellow; in this case it may 
consist either of sulphuret of cadmium, or a sulphuret of 
arsenic, or bisulphuret of tin, and indicates therefore the 
presence either of cadmium, or of arsenic, or of peroxide of 
tin. To distinguish them, ammonia in excess is added to 
the fluid, wherein the precipitate is suspended. 

act. The precipitate does not disappear ; cadmium is 
present, sulphuret of cadmium being soluble in ammonia. 
The blow-pipe is resorted to for further proof. (§ 91, d.) 

hb. The precipitate disappears. It consists either of 
peroxide of tin or of arsenic. Ammonia is added to a 
portion of the original solution. 

act. A white precipitate is formed. Peroxide of 
tin is the substance present. Asa conclusive proof, 
the precipitate is then mixed with cyanide of potas- 
sium and carbonato of soda, and reduced before the 
blow-pipe. (§ 94, b.) 

fift. No precipitate is formed. This indicates the 
presence of arsenic. The real presence of the arsenic 
may then be ascertained by the production of a me- 
tallic crust, either from the original substance, or 
from the precipitated sulphuret of arsenic, mixed with 
cyanide of potassium and carbonate of soda, or in 
some other way, and also by mixing the original sub- 
stance with carbonate of soda, and exposing it to the 
reducing flame of the blow-pipe. (§ 94, d.) 
y. The precipitate is orange-coloured ; in this 
case it consists of sulphuret of antimony, and indicates the 
presence of oxide of antimony. The blow-pipe is re- 
sorted to for further proof. (§ 94, a.) 

S . The precipitate is brown. It consists of sul- 
phuret of tin, and indicates the presence of protoxide of 


DETECTION OF THE BASES. 


191 


tin. For conclusive proof, one portion of the original 
solution is tested with solution of perchloride of mercury, 
and another with solution of gold. (§ 94, b.) 

e. The precipitate is black. It may in this case 
consist of sulplmret of lead, or sulpliuret of copper, or sul- 
phuret of bismuth, or sulpliuret of gold, or sulpliuret of 
platinum, or bisulphuret of mercury. To distinguish these 
from each other, the following experiments are made with 
the original solution. 

aa. Dilute sulphuric acid is added to a portion of it ; 
a white precipitate is formed ; this indicates the presence 
of lead. Chromate of potash is employed as a. conclu- 
sive test. (§ 90, c.) 

bb. Ammonia in excess is added to a, portion of it. A 
blue precipitate is formed which redissolves in the excess 
of the precipitant, imparting an azure colour to the so- 
lution ; this indicates copper. Ferrocyanide of potas- 
sium is resorted to as a conclusive test. (§ 91, b.) 

cc. Potash is added to a portion of it ; a yellow pre- 
cipitate is formed ; this indicates tho presence of peroxide 
of mercury. Protochloride of tin and metallic copper aro 
employed as conclusive tests. (§ 91, a.) The presence 
of peroxide of mercury may generally also be detected 
by the precipitate which it yields with sulphuretted 
hydrogen, not appearing black from the beginning, but 
on the addition of an excess of the precipitant, passing 
through white, yellow, and orange, and then at last 
changing its colour into black. (§ 91, a, 2.) 

del. A portion of the original solution is evaporated 
nearly to dryness, in a porcelain crucible, and the re- 
sidue put into a test tube, half filled with water. If the 
solution becomes milky, a basic salt of bismuth i3 pre- 
sent; this reaction therefore indicates bismuth. Tho 
blow-pipe is resorted to, as a conclusive test. (§91, c.) 

ee. Solution of sulphate of iron is added to a portion 
of the original solution. A fine black precipitate is in- 

0 


192 


SUBSTANCES SOLUBLE IN WATER. 


dicativc of the presence of gold. The blow-pipe is re- 
sorted to ns a conclusive test , or the original solution is 
tested with protochloride of tin. (§ 93, a.) 

ff. Chloride of potassium is added to a portion of the 
original solution ; the formation of a yellow olirystalline 
precipitate is indicative of the presence of platinum. 
For further proof this precipitate is heated to redness 
(§ 03, b.) 

3. To the fluid in which sulphuretted hydrogen has not pro- 
duced any precipitate, or — should this have become too dilute — 
to a portion of the original solution, afhmonia is added, till the 
solution has an alkaline reaction ; hydrosulphuret of ammonia is then 
added. (If the solution was not acid, and thus no ammoniacal 
salt has been formed on the addition of ammonia, the addition of 
the hydrosulphuret of ammonia is preceded by that of sal ammoniac.) 

a. No precipitate is formed ; pass over to § 107, 4 ; for 
iron, cobalt, nickel, manganese, zinc, chromium, and alumina 
are not present. 

b. A precipitate is formed. 

«. The precipitate is black ; protoxide of iron, nickel, 
or cobalt. A portion of the original solution is treated 
with caustic potash. 

aa. A dirty greenish white precipitate is obtained, 
which soon changes into a reddish-brown, when exposed 
to the air : protoxide of iron. Ferricyanide of potas- 
sium is resorted to as a conclusive test. (§ 88, e .) 

hh. A precipitate of a light greenish tint is produced, 
which does not change its colour : nickel. Ammonia 
and addition of potash are resorted to as conclusive 
tests. (§ 88, c.) 

cc A sky-blue precipitate is formed, which changes 
its tint into red, on boiling : cobalt. The blow-pipe is 
resorted to as a conclusive test. (§ 88, cl.) 
ft. The precipitate is not black. 

aa. If the precipitate is of a clear flesh colour, it con- 
sists of sulphuret of manganese, and is therefore indica- 


DETECTION OF THE BASE. 


193 


tive of the presence of protoxide of manganese. The 
addition of potash to the original solution, or the blow- 
pipe, are resorted to as conclusive tests. (§ 88, b.) 

bb. If the precipitate is bluish-green, it consists of 
hydrated oxide of chromium. The addition of potash 
to the original solution, and the blow-pipe, are resorted 
to as conclusive tests. (§ 87, b.) 

cc. If the precipitate is white, it may consist either of 
hydrate of alumina, or of sulphuret of zinc, and thus 
be indicative of the presence either of alumina or of 
oxide of zinc. To distinguish these, solution of 
potash is gradually dropped into a portion of the 
original solution, till the precipitate is redissolved, and 
then 

«a. Solution of sulphuretted hydrogen is added to 
a portion of it ; the formation of a white precipitate 
is indicative of the presence of zinc. For further 
proof, the reaction with solution of cobalt before the 
blow-pipe is selected. (§ 88, a.) 

00 . Muriate of ammonia is added to another 
portion of the alkaline solution. The formation of a 
white precipitate is indicative of the presence of 
alumina. The test with solution of cobalt before the 
blow-pipe is selected as a conclusive proof. (§ 87, a.) 

Note to § 107. 3. 0. 

As very slight contaminations may impair the distinctness of 
the tints which the precipitates considered under § 107. 3. b. 
0. present, it is advisable where such are suspected to adopt 
the following method for the detection of manganese, chromium, 
zinc, and alumina. 

Potash in excess is added to a portion of the original solution. 
act. A whitish precipitate is formed, which is not re- 
dissolved in an excess of the precipitant, and soon changes 
its colour to a blackish brown when exposed to the air : 

o 




194 


SUBSTANCES SOLUBLE IN WATER. 


manganese. The blow-pipe is resorted to as a conclusive 
test. (§ 88, b.) 

bb. A precipitate is formed which redissolves in an excess 
of the precipitant : oxide of chromium, alumina, zinc. 

aa. Sulphuretted hydrogen is added to a portion of 
tho solution with potass. The formation of a white 
precipitate indicates the presence of zinc. 

ftft. If tho original or solution with potass appear 
green, and the precipitate, first produced by potash and 1 
then redissolved in the excess of the precipitant, was 
bluish, oxide of chromium is present. For further 
proof the solution with potass may be boiled, or the 
blow-pipe resorted to. (§ 87, b.) 

yy. Muriate of ammonia is added to the solution 
with potass. Tho formation of a white precipitate in- 
dicates the presence of alumina. The test witli solu- 
tion of cobalt before the blow-pipe is selected as a 
further proof, (§ 87, a.) 

4. Muriate of ammonia and carbonate of ammonia, mixed 
with a small quantity of caustic ammonia, are added to a portion 
of the original solution, which is then boiled. 

a. No precipitate is formed : absence of barytes, 
strontian, and lime. Pass over to § 107, 5. 

b. A precipitate is formed. Presence of barytes, 
strontian, or lime. Solution of gypsum is added to a portion 
of the original solution, and heat applied. 

a. The solution does not become turbid, even after the 
lapse of Jive to ten minutes : lime. The test with oxalic 
acid is selected for further proof. (§ 86, c.) 

ft. The solution does not become turbid at first, but 
after the lapse of some time: strontian. The alcohol > 
flame is resorted to as a conclusive test. (§ 86, b.) 

y. A precipitate is immediately formed: barytes, r* 
For further proof test with hydrofiuosilicic acid. (§ 86, a.) . 

5. Phosphate of soda is added to the solution of (4) in which! 
carbonate of ammonia, after the addition of muriate of ammonia <: 
has produced no precipitate. 


DETECTION OF INORGANIC ACIDS. 


195 


a. No precipitate is formed, not even after agitating 
the solution: absence of magnesia. Pass over to § 107, 6. 

b. A FINE CRYSTALLINE PRECIPITATE IS FORMED: MAG- 
NESIA. » 

0. A drop of the original solution is evaporated on a platinum 
plate and the residue heated to redness. 

a. No fixed residue remains. The original solution 
is tested for ammonia, by adding potash to it, and ex- 
amining the odour, the vapours formed with acetic acid, and 
the reaction of the escaping gas. (§ 85, c.) 

b. A fixed residue remains. Potash or soda. Tar- 
taric acid is added to a portion of the original solution, and 
the latter well shaken. 

a. No precipitate is formed , not even after the lapse of 
ten to fifteen minutes : soda. The blow-pipe flame and 
alcohol flame, and especially the reaction with antimoniate 
of potash, are selected as conclusive tests. (§ 85, b.) 

ft. A crystalline granular precipitate is formed : potash. 
Chloride of platinum, the blow-pipo flame, and alcohol 
flume, are selected as conclusive tests. (§ 85, a.) 

Compounds which are supposed to contain but one acid 
and one base, dc. 

A. substances soluble in water, detection of the ACID. 

I. Detection of inorganic acids. 

§ 108. 

We must in the first place consider what acids form combina- 
tions soluble in water, with the base detected, and bear it in mind 
in the subsequent examination. 

1. We have already spoken of the detection of the arsenious 
and arsenic acid in treating of the detection of the bases. They 
are distinguished from each other by their behaviour with nitrate 
of silver, or with potash and sulphate of copper. (§ 94, d and e.) 

2. The detection of carbonic acid, iiydrosulfhuric acid 

o 2 



190 


SUBSTANCES SOLUBLE IN WATER. 


and chromic acid, has also already been pointed out, when treat- 
ing of the detection of the bases. The two former betray their 
presence by effervescing on the addition of hydrochloric acid ; they 
may he distinguished from each other by their odour, and if 
needed, the presence of carbonic acid may he proved by its re- 
action with lime-water, (§99, a,) and that of sulphuretted hydro- 
gen by the reaction with solution of lead. (§ 100, e.) Chromic 
acid may in most cases he detected by the yellow or red tint of 
its solution, and also by its solution changing colour and yielding 
a precipitate of sulphur, on the addition of sulphuretted hydrogen. 
We may assure ourselves of the presence of chromic acid by the 
reaction with solution of lead, and solution of silver. (§ 90. 1.) 

3. Chloride of barium is added to a portion of the solution ; 
should the latter have an acid reaction, it must first be neutralized 
or rendered feebly alkaline, by the addition of ammonia. 

a. The fluid remains clear. (Pass over to § 108, 4.) 
The absence of sulphuric acid, phosphoric acid, and silicic 
acid is certain, that of oxalic acid and boracic acid, probable. 
For the barytes compounds of these two latter acids are kept 
in solution by ammoniacal salts, and borate of barytes does 
not at all precipitate from dilute solutions. 

l>. A precipitate is formed. Hydrochloric acid is 
added in excess. 

a. The precipitate redissolves. Absence of sulphuric 
acid. Pass over to 4. 

/3. The precipitate remains and does not dissolve even 
in a large proportion of water : sulphuric acid. 

4. Solution of gypsum is added to a portion of the original 
solution, which, should it have an acid reaction, must first be 
rendered neutral or feebly alkaline, by the addition of ammonia. 

a. No precipitate is formed : absence of oxalic acid 
and phosphoric acid. Pass over to § 108, 5. 

b. A precipitate is formed. Acetic acid is added in 
excess. 

a. The precipitate is redissolved : phosphoric acid . j 
The reactions with sulphate of magnesia and ammonia. 


DETECTION OF INORGANIC ACIDS 


197 


with solution of silver, and before the blow-pipe, are 
selected as conclusive tests. (§ 98, a.) 

fl. The precipitate remains undissolved, but dissolves 
readily in hydrochloric acid : oxalic acid. The reaction 
with concentrated sulphuric acid is selected as a conclusive 
test. (§ 98, c.) 

5. A fresh portion of the original solution is acidified with 
nitric acid, and solution of nitrate of silver is then added. 

a . The fluid remains clear. This is a certain indi- 
cation of the absence of chlorine and iodine. The absence 
of cyanogen is also probable. For cyanide of mercury is not 
precipitated by nitrate of silver ; and from the detected base 
we may conclude whether we have to look for the presence of 
this substance or not ; for the manner in which the presence 
of the cyanogen in it is proved, we refer to § 100, d. Pass 
over to § 108, 6. 

h. A PRECiriTATE is formed. Ammonia is added in 
excess. 

a. The precipitate does not dissolve: iodine. As a 
conclusive test we select the reaction with starch. (§ 
100, c.) 

ft. The precipitate is redissolved. If it redissolves 
readily, we have reason to suppose that chlorine is pre- 
sent ; if it dissolves with difficulty and only on the addi- 
tion of much ammonia, we may suppose that cyanogen is 
present. We assure ourselves of the presence of chlorine, 
by testing the original solution with protonitrate of mercury, 
and by the behaviour of the silver precipitate formed when 
exposed to a high temperature. (§ 100, a.) The presence 
of cyanogen may be further proved by adding potash, 
solution of magnetic oxide of iron and hydrochloric acid 
to the original solution. (§ 100, d.) 

0. A portion of the solid substance — (or if we have a fluid to 
operate upon, the residue obtained by evaporation) — is drenched 
with some sulphuric acid, alcohol added and then kindled. 
Poracic acid is present if the flume appears green on stirring. 


198 


SUBSTANCES SOLUBLE IN WATER. 


7. The preliminary examination generally enables us to detect 
nitric acid. (§ 105, A, I. 2, c.) The reactions with sulphate of 
iron and sulphuric acid, or solution of indigo, are selected as con- 
clusive proofs. (§ 101, a.) 

8. Wo refer to § 123 for the detection of chloric acid, hydro- 
fluoric acid, silicic acid, and bromine. 


Compounds which ice suppose to contain only one acid and one 

base, dec. 

A. Substances soluble in water. Detection of 

the ACID. 

II. DETECTION OF ORGANIC ACIDS. 

§ 109. 

1 . To a portion of the aqueous solution, ammonia is added till 
a feeble alkaline reaction becomes manifest, and then chloride of 
calcium. If we have to operate upon a neutral solution, some 
muriate of ammonia is added to it, previous to the addition of the 
chloride of calcium. 

a. No PRECIPITATE IS FORMED, NOT EVEN AFTER AGI- 
TATING THE SOLUTION, NOR AFTER THE LAPSE OF A FEW 
minutes : absence of oxalic acid and tartaric acid. Pass 
over to § 109, 2. 

b. A precipitate is formed. Lime-water is added in 
excess to a portion of the original solution, and the preci- 
pitate formed treated with solution of sal ammoniac. 

a. The precipitate vanishes : tartaric acid. The re- 
action with acetate of potash may he resorted to for further 
proof ; hut the safest test is the behaviour of the preci 
pitate produced by chloride of calcium, with caustic potash. 
(§ 102 , b.) 

ft. The precipitate does not vanish : oxalic acid. 

2. The fluid of 1, a, is heated to boiling, kept at the boiling 
point for some time, and some ammonia added (whilst boiling). 


DETECTION OF ORGANIC ACIDS. 


199 


a. It remains transparent : no citric acid. Pass over 
to § 109, 8. 

b. It BECOMES TURBID, AND DEPOSITS A PRECIPITATE : 
CITRIC ACID. 

3. The fluid of 2, a, is mixed with alcohol. 

a. It remains transparent : no malic acid. Pass over 
to § 109, 4. 

b. A precipitate is formed : malic acid. The re- 
action with acetate of lead is selected as a conclusive test. 
(§ 102, e.) 

4. A portion of the original solution, is rendered perfectly 
neutral — (if it is not already so) — by ammonia or hydrochloric 
acid, and solution of perchloride of iron added. 

a. A cinnamon-coloured or dirty yellow bulky 
precipitate is formed. This precipitate is treated with 
dilute hydrochloric acid. 

a. It dissolves transparent : succinic acid. 

/3. It dissolves, with the separation of a white preci- 
pitate : benzoic acid. We assure ourselves of the real 
presence of this substance, by heating the precif itate. It 
must manifest the properties of free benzoic acid. (Vide 
§ 103, b.) 

b. The liquid assumes an intense red tint, and 
UPON BOILING FOR SOME TIME, A LIGHT REDDISH-BROWN 
PRECIPITATE SEPARATES: acetic acid or formic acid. A 
portion of the solid salt under examination, or the residue 
obtained by evaporating the liquid — (if the liquid is acid, it 
must be neutralized with potash, previous to the evaporation) 
— is heated with sulphuric acid and alcohol, (§ 104, a.) 
The characteristic odour of acetic ether, indicates the pre- 
sence Of ACETIC ACID. 

If we do not detect acetic acid in the fluid, we must con- 
clude that the substance under examination contains formic 
acid : the certain presence of this latter substance may be 
proved by its behaviour with nitrate of silver and protoxide 
of mercury. (§ 104, b.) 


200 


SUBSTANCES INSOLUBLE IN WATER. 


Compounds which are supposed to consist of hut one acid 
and one base, dc. 

B. Substances insoluble or sparingly soluble in water, 
BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR 
AQUA REGIA. 

Detection of the base * * * § 

§ 110 . 

A portion of the solution in hydrochloric acid, nitric acid, or 
aqua regia, is diluted with water, t and the further operations con- 
ducted exactly as directed § 107, beginning at 1, when the sub- 
stance is dissolved in nitric acid, and at 2, when it contains 
already hydrochloric acid. The following circumstances must be 
well attended to : We have seen that if in cases where we have 
a substance soluble in water before us, we obtain, in the course 
of the examination, a white precipitate on testing with hydrosul- 
phuret of ammonia — (after having neutralized with ammonia the 
free acid either originally contained in or previously added to the 
solution under examination) — this precipitate can consist only 
either of sulphuret of zinc, or of alumina. But the case is differ- 
ent, when the substance is insoluble in water, hut dissolved 
by hydrochloric acid ; for in that case the white precipitate pro- 
duced by liydrosulplmret of ammonia, with the presence of sal 
ammoniac, may also consist of a phosphate of the alkaline earths 
as well as of oxalate of lime, (barytes and strontian.) If therefore 
we obtain a white precipitate when testing an acid solution, under 
the circumstances stated, and as directed § 107, at 3 /l. cc, the 
following method must be employed. Caustic potash in excess is 
added to a small portion of the original hydrochloric solution. 

* Regard has here been had also to sevaral salts, since this course of ex- 

amination directly leads to their detection. 

f If on the addition of the water, the liquid becomes turbid or is preci- 
pitated, it indicates the presence of antimony, bismuth, or tin. (Compare 

§ 105, B 4.) 


DETECTION OF THE BASE. 


201 


]. The PRECIPITATE AT FIRST FORMED, REDISSOLVES IN EX- 
CESS of the precipitant ; absence of the salts of the alkaline 
earths ; presence of zinc or of alumina : to distinguish these from 
ercli other, the solution with potass is tested wi th sulphuretted 
hydrogen and muriate of ammonia. (Vide supra § 107, 3 b. /3. cc.) 
Alumina may have been present and precipitated as phosphate of 
alumina. This is ascertained by dissolving the precipitate in 
hydrochloric acid, adding tartaric acid, supersaturating with ammo- 
nia and mixing with sulphate of magnesia. If phosphoric acid is 
present, a precipitate of basic phosphate of ammonia and mag- 
nesia is formed. 

2. The precipitate formed does not redissolve in an 
excess of the precipitant. Presence of a phosphate or oxa- 
late with an alkaline earth for its base. In this case a portion of 
the original substance is heated to redness, in order to ascertain 
yhether we have an oxalate or a phosphate before us. If the sub- 
stance is converted by this process into a carbonate — (slightly 
blackening or not at all) — which is easily detected by 
the heated mass effervescing when treated with acids, whilst 
previous to the heating it did not present this property, we 
may conclude that the salt is an oxalate ; if, on the contrary, no 
alteration takes place, on the application of a red heat, we have a 
PnosniATE before us. 

a . This preliminary examination denoted the pre- 
sence OF A PHOSPHATE. 

A certain, not to oinconsiderable quantity, of percliloride of 
iron is added to a portion of the hydrochloric solution, which 
is then brought to alkalino reaction by the addition of am- 
monia, and the liquid filtered off from the bulky precipitate 
formed, which should present a reddish-brown tint. In this 
operation the phosphoric acid is separated from its base and, 
combined with peroxide of iron, precipitated together with 
free hydrate peroxide of iron, whilst the alkaline earth base 
is contained in the filtered liquid as a chloride. The further 
process of the detection of this base is conducted as directed 
§ 107, 4. 


202 


SUBSTANCES INSOLUBLE IN WATER. 


In order to determine the presence of the phosphoric acid 
also, the iron precipitate is rinsed, and digested with hydro- 
sulphuret of ammonia. We obtain in this process sulphuret 
of iron and phosphate of ammonia. These are separated 
from each other by filtration, and sal ammoniac and sulphate 
of magnesia is then added to the filtered liquid ; the precipi- 
tate which forms, of basic phosphate of ammonia and mag- 
nesia, is a safe indication of the presence of phosphoric acid. 
In more minute examinations, the excess present of hydro- 
sulphuret of ammonia is first decomposed by the addition of 
hydrochloric acid, the solution heated to boiling, and the pre- 
cipitated sulphur filtered off ; the filtered solutions, if needed, 
concentrated by evaporation, supersaturated with ammonia, 
and sulphate of magnesia then added. 

b . The preliminary examination indicated the pre- 
sence OF AN OXALATE. 

Two methods may be pursued, with certainty, to detennino 
the base and the acid. 

1 . A portion of the compound is heated to redness, the 
residue dissolved in hydrochloric acid, and the alkaline 
earth which forms the base, detected in the usual manner 
in this solution. Of the presence of the oxalic acid we 
assure ourselves by testing another portion of the substance 
with concentrated sulphuric acid. (§ 98, c.) 

2. A portion of the compound is boiled for some time 
in a concentrated solution of carbonate of potash, and the 
fluid filtered from the residue. In this manner we obtain 
in the residue the alkaline earth which forms the base of the 
substance under examination, combined with carbonic acid, 
whilst we have the oxalic acid combined with potash in the 
filtered solution ; to assure ourselves of the real presence 
of this acid, the solution is first acidified with acetic acid, 
and then treated with solution of gypsum. (§ 98, c.) Tho 
residue is rinsed and dissolved in hydrochloric acid, and 
the solution treated as directed § 107, 4. 


10 




DETECTION OF INORGANIC ACIDS. 


203 


Compounds which are supposed to consist of but one acid and 

one base, dc. 

13. Substances insoluble or sparingly soluble in water, 

BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR AQUA 
REGIA. 


DETECTION OF THE ACID. 

I. Detection of inorganic acids. 

§ 111 . 

1. Chloric acid cannot be present, for all chlorates arc solu- 
ble in water; the nitrates also, with the exception of a few r , being 
soluble in water, wo may generally disregard the presence of 
nitric acid. The basic nitrate of bismuth forms the most fre- 
quently occurring exception to the general rale of solubility of 
the nitrates in water. The presence of nitric acid in such inso- 
luble compounds may be immediately detected by deflagration 
taking place when the substance under examination is thrown 
upon red-hot charcoal. The deflagration which ensues on fusing 
a nitrate together with cyanide of potassium, is a safer test of 
the presence of nitric acid. (Vide § 101, a.) For the cyanides 
insoluble in water, we refer to § 128. 

2. The detection of arsenious and arsenic acid, carbonic 
acid, hydrosulpiiuric acid, and chromic acid, has already been 
pointed out, when treating of the detection of bases ; as the best 
tests and indications of the presence of chromic acid, we have 
pointed out the yellow or red colour of the compound, the evolu- 
tion of chlorine, upon a chromate being boiled with hydrochloric 
acid, and the subsequent detection of chromic oxide in the solu- 
tion. But the safest method, and that which is applicable in all 
cases, is to fuse the substance supposed to contain chromic acid, 
together with some carbonate of soda and nitre. (§ 90, b.) 


201 


SUBSTANCES INSOLUBLE IN WATER. 


3. A portion of the substance under examination is boiled with 
nitric acid. 

a. If nitric oxide gas is evolved, which is easily detected by 
the red fumes of nitrous acid, formed on coming in contact 
with the air, it indicates the presence of a sulphuret; if i 
carbonic acid is evolved, that of a carbonate. Of the pre- 1 
sence of a sulphuret we may easily assure ourselves, by 
testing the nitric solution with chloride of barium ; it should 
yield with this reagent a precipitate of sulphate of barytes, 
which must remain undissolved even in a large quantity of 
water. Sulphurets may as safely be detected by their beha- 
viour before the blow r -pipe. (Vide § 100, c.) 

b. If violet vapours escape, the compound may be sup- 
posed to be an iodide. A slip of paper, covered with 
starch, forms the best conclusive test of the presence of 
iodine. (§ 100, c.) 

4. Nitrate of silver is added to a portion of the nitric solu- 
tion, (this solution must previously be filtered, if upon treating 
the substance with nitric acid any insoluble residue has remained.) 

If a white precipitate is formed, soluble in ammonia, and fusing 
without decomposition when heated, it indicates the presence of 
CHLORINE. 

5. A portion of the substance is boiled with hydrochloric acid, 
filtered, if needed, and nitrate of barytes added. The formation 
of a white precipitate, which does not disappear, even on the 
addition of a large proportion of water, indicates the presence of 
sulphuric acid. 

G. For boracic acid, test as stated supra, § 108. 

7. If none of all these acids is present, we have reason to sup- 
pose the presence of either phosphoric acid or oxalic acid, or 
the absence of all acids. If the phosphoric acid had been com- 
bined with an alkaline earth, and the oxalic acid with lime, 
(barytes, or strontian,) either of them would have already been 
detected wdien testing for these bases. (§ 110.) We may there- 
fore disregard the presence of these two acids, except w’hen other 
buses than those enumerated are present. In the latter case 


DETECTION OF ORGANIC ACIDS. 


205 


the fluid is prepared for further examination by precipitating and 
separating the heavy metals from it — (this is effected in acid 
solutions by means of sulphuretted hydrogen, and in alkaline 
solutions by hydrosulphuret of ammonia) — and is then tested for 
phosphoric acid or oxalic acid, as directed § 108, 4. 

8. For the detection of silicic acid, bromine, and fluorine, 
vide § 123, at the end. 


Compounds which are supposed to consist of but one base and one 

acid, dec. 

B. Substances insoluble or sparingly soluble in water, 

BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACIl), OR AQUA 
REGIA. 


DETECTION OF THE ACID. 

IT. Detection of organic acids. 

§ 112 . 

1 . A portion of the substance under examination is dissolved 
in the smallest possible quantity of hydrochloric acid. If a re- 
sidue remains, this must be tested for benzoic acid by heating. 
Carbonate of potash in excess is then added to the hydrochloric 
solution, and the latter boiled for some time and filtered. The 
alkaline filtrate contains the organic acid, under all circumstances. 
This filtered solution is therefore exactly saturated with hydro- 
chloric acid, and the fluid tested, as directed § 109. No regard 
need be had to formic acid, all the formiates being soluble in 
water. 

2. Acetic acid is most readily detected in such compounds by 
means of sulphuric acid and alcohol. (§ 104, a.) 


200 


DETECTION OF BOTH THE BASE AND THE ACID. 


Compounds which are supposed to consist of but one acid and 

one base, dec. 

C. Substances insoluble or sparingly soluble in water, 

HYDROCHLORIC ACID, NITRIC ACID, AND AQUA REGIA. 

DETECTION OF THE BASE AND THE ACID. 

§ ] 13 . 

Under this head we propose to consider sulphate of barytes, 
SULPHATE OF STRONT1AN, SULPHATE OF LIME, SILICA, SULPHATE 
OF LEAD, CHLORIDE OF LEAD, aild CHLORIDE OF SILVER, AS the 
most frequently occurring compounds belonging to this class. 
For the less frequently occurring compounds of this kind, we 
refer to § 127. 

Sulphate of lime and chloride of lead are not altogether inso- 
luble in water, and sulphate of lead may he dissolved in hydro- 
chloric acid. As these compounds arc, however, so sparingly 
soluble that we seldom can effect their complete solution, we 
mention them here once more, in order that they may be detected 
by the method laid down in this section, should they have es- 
caped detection in the examination of their aqueous or acid 
solutions. 

1. A very minute quantity of the substance under examination 
is treated with hydrosulphuret of ammonia. 

a. It becomes black ; this indicates the presence of a 
salt of lead or chloride of silver. A somewhat larger 
portion of the substance is then digested for some time with 
hydrosulphuret of ammonia. In this process the metallic 
salt becomes decomposed, and a sulpliuret is formed, which 
remains undissolved, whilst we have in solution the acid of 
the metallic salt combined with the ammonia of the hydro- 
sulphuret of ammonia. The solution is then filtered, the 
undissolved sulphuret washed and dissolved in nitric acid, 
and this nitric solution tested, with sulphuric acid, for lead ; 


DETECTION OF BOTH THE BASE AND THE ACID. 


207 


and with hydrochloric acid, and subsequent addition of 
ammonia, for silver. One portion of the filtered liquid is 
tested for sulphuric acid, with chloride of barium, after 
having previously decomposed the excess of the liydrosul- 
phuret of ammonia, by the addition of hydrochloric acid and 
boiling up ; another portion is tested for hydrochloric 
acid, with solution of silver, after having previously acidi- 
fied the liquid with nitric acid, and then boiled it. 

b. It becomes white. Absence of a heavy metallic 
oxide. A small portion of the substance under examination 
is reduced to a very fine powder, and then mixed with four 
times its quantity of carbonate of soda and potash, put into 
a small platinum crucible, and fused over a Berzelius spirit- 
lamp. The fused mass is boiled with water. 

a. Complete solution takes place: silica. We assure 
ourselves of the presence of this substance by supersaturat- 
ing the solution with hydrochloric acid, and evaporating to 
dryness. In this operation, silicic acid is converted from its 
soluble into its insoluble modification. It remains, there- 
fore, un dissolved on treating the residue with water. 
When mixed with carbonate of soda, and exposed to a 
strong blow-pipe flame, a transparent glass is produced. 

(§ 99 , b.) 

fi. A white residue remains; this indicates one of the 
SULPHATES OF THE ALKALINE EARTHS. The Solution is 
filtered, and the filtered liquid acidified with hydrochloric 
acid, and then tested for sulphuric acid, with chloride of 
barium. The white residue (which contains the alkaline 
earth as a carbonate) is carefully washed, dissolved in a 
small quantity of dilute sulphuric acid, and the solution 
tested for barytes, strontian, or lime, as directed 
§ 107 , 4 . 


208 


SUBSTANCES SOLUBLE IN ACIDS. 


Compounds in which all the more frequently occurring Bases, 
Acids, Metals, and Metalloids, are supposed to be present. 

A. Substances both soluble and insoluble in water, and 

SOLUBLE IN HYDROCHLORIC ACID OR NITRIC ACID. 

Detection of the bases.* 

§ 114 . 

In this scheme for the testing of the bases, we have united the 
compounds belonging to classes I. and II., (vide § 100,) since the 
method of detection is in most cases the same for both classes. 
Those parts which refer only to substances insoluble in water, and 
soluble in hydrochloric acid and nitric acid, are enclosed between 
inverted commas (“ ”), and may therefore he passed over un- 

noticed, when examining substances, soluble in water. 

I. The solution is aqueous. 

A small quantity of hydrochloric acid is added. 

1. The solution had an acid or neutral reaction pre- 
vious TO THE ADDITION OF THE HYDROCHLORIC ACID. 

a. No precipitate is formed : this indicates the ab- 
sence of silver and protoxide of mercury. Pass over to 

§ 115 . 

b. A precipitate is formed ; hydrochloric acid is added 
to the solution drop by drop, as long as the quantity of the 
precipitate increases. This precipitate may consist of chloride 
of silver, protochloride of mercury, chloride of lead, ora basic 
salt of antimony, or, possibly, also of benzoic acid. The fluid 
is agitated, and a portion of it, together with the therein sus- 
pended particles of the precipitate, mixed with a large quan- 
tity of water, and heated to boiling. If compounds of anti 

* The arsenious and arsenic acid, and several salts, have here been had 
regard to, since we are, in this course of examination, led to their detection. 


DETECTION OF THE BASES. 


200 




mony, bismuth, or tin arc present, the dilution with water may 
render the liquid turbid, which phenomenon is usually dis- 
tinctly perceived, notwithstanding the precipitate which the 
fluid already contained previous to the addition of the water. 
In order to judge with certainty, whether the precipitate pro- 

I duced by hydrochloric acid redissolves in the water on boil- 
ing or not, and therefore, whether the further operation is to 
be conducted according to a, or ft, hydrochloric acid is added 
to the dilute solution — (previous to heating) — till the milki- 
ness has completely vanished. 

a. The precipitate vanishes; this indicates the absence 
of silver and protoxide of mercury. The original solution, 
together with the precipitate produced in it by hydrochloric 
acid is heated to boiling and filtered hot. Should the pre- 
cipitate not completely redissolve, the residue is once more 
boiled with water, and the solution filtered hot into the first 
filtrate. The filtered solution is treated as directed § 115 . 
Should it have deposited a precipitate, or small crystals 
(chlorido of lead) have formed on cooling, it must be previ- 
ously heated, till it appears transparent again. 

ft. The precipitate does not vanish, at least not com- 
pletely ; this indicates the presence of silver or protoxide 
of mercury. 

The original solution (with the hydrochloric acid) is treated as 
1 directed § 114 , I. 1, b, a. The residuary insoluble precipitate is 
| washed and tested as follows : it is, if possible, removed from the 
filter and treated with ammonia, in a small tube. If it dissolves 

f in this substance, it consists exclusively of silver ; if it becomes 
black, protoxide of mercury is present. In this case, or when- 
\ ever a residue insoluble in ammonia remains, this must be filtered 
off, and nitric acid in excess added to the filtered liquid ; the for- 
mation of a white, curdy precipitate indicates silver. 

2. The aqueous solution had an alkaline reaction. 

a. No evolution of gas takes place and no preci- 
pitate is formed, on the addition of hydrochloric 

ACID, OR, A PRECIPITATE IS AT FIRST FORMED, BUT REDIS- 




P 


210 


DETECTION OF THE DASES. 


SOLVES ON THE FURTHER ADDITION OF HYDROCHLORIC ACID ; 
pass over to § 115. For all tlmt relates to substances be- 
longing to the second class — (i. e. those insoluble in water, 
and soluble in hydrochloric acid or nitric acid) — enclosed 
between inverted commas, look to the passages upon phos- 
phate of alumina, but, if an ammoniacal salt is present, 
also to those upon the oxalates of tho alkaline earths, since 
the solution of these compounds in a fluid with alkaline re- 
action is not impossible. 

b. A PRECIPITATE IS FORMED, ON THE ADDITION OF 
HYDROCHLORIC ACID, WHICH DOES NOT REDISSOLVE IN AN 
EXCESS OF THE PRECIPITANT. 

a. The precipitate is formed without simultaneous evo- 
lution of sulphuretted hydrogen gas. A portion of the 
fluid with the precipitate suspended therein, is diluted with 
a large proportion of water, and heated. The solution of 
tho precipitate is indicative of lead, or possibly also of 
benzoic acid. The original solution is then heated to boil- 
ing, together with the precipitate produced by hydrochloric 
acid, filtered hot, and tho residue (if any remain) boiled 
with water and filtered hot into tho hydrochloric solution. 
The filtrate is treated according to § 115; should it be- 
come turbid on cooling, it must be heated again previous 
to being further tested. If the precipitate does not redis- 
solve on heating the fluid diluted with water, but is dis- 
solved by ammonia, silver is present. The original solu- 
tion is treated in the same manner as if the precipitate had 
been redissolved. 

P>. The precipitate is formed with simultaneous evolu- 
tion of sulphuretted hydrogen gas. 

aa. The precipitate is of a pure white colour, and con- 
sists of sulphur. In this case an alkaline bisulphuret 
is present. Filter the solution and pass over to § 118, 
bearing in mind that of the substances considered § 118, 
oxide of chromium and alumina alone can be present. 
bb. The precipitate is coloured. In this case we must 


DETECTION OF THE BASES. 


211 


suppose that a metallic sulphur salt is present, i. e. a 
combination of an alkaline sulphur base with an electro- 
negative sulphuret. The solution is heated to boiling 
and filtered ; the filtrate is further tested as stated under 
aa. The precipitate is treated as § 110 directs ; it may- 
consist of SULPIIDRET OF GOLD, SULPHURET OF PLATI- 
NUM, SULPHURET OF TIN, SULPHURET OF ARSENIC, OR 
SULPHURET OF ANTIMONY. 

C. NO LASTING PRECIPITATE IS FORMED, ON THE ADDITION 
OF HYDROCHLORIC 'ACID, BUT EVOLUTION OF GAS TAKES 
PLACE. 

a. The escaping gas has the odour of sulphuretted 
hydrogen ; this indicates a simple alkaline sulphur com- 
pound. The further operations are conducted as di- 
rected aa. 

ft. The escaping gas emits no odour ; in this case it is 
carbonic acid which was combined with an alkali. Pass 
over to § 115, bearing in mind, that mercury, bismuth, 
insoluble salts of magnesia, and (if the reaction is strongly 
alkaline) barytes, strontian, and lime cannot bo pre- 
sent, or at least only under very peculiar circumstances, 
(e. g. mercury as a cyanide.) 

II. The solution is hydrochloric. 

It is treated as § 115 directs. 

III. The solution is nitric. 

A small portion of it is diluted with much water. 

1. It remains transparent; add hydrocldoric acid. 

a. No precipitate is formed. Absence of silver. The ori- 
ginal solution is treated according to § 115. 

h. A precipitate is formed. If it does not redissolve on 
heating the fluid, but is dissolved by ammonia, after washing, 
silver is present. The original solution is treated as stated 
§ 115. 

2. The solution becomes turbid and milky : bismuth or 

P 2 


212 


DETECTION OF THE BASES. 


antimony. The fluid is filtered, and the filtrate tested for silver . 
according to § 114, III. 1; the original solution is tested as ; 
§ 1 1 5 directs. 

. 

§ 115. j;; 

Solution of sulphuretted hydrogen is added to a small portion 
of the transparent acid solution, till the fluid, after agitation, 
and application of heat, emits a clearly perceptible odour of sul- 
phuretted hydrogen. 

a. No precipitate is formed, not even after the lapse of 
sometime. Pass over to § 118, for neither lead, bismuth, 
cadmium, copper, mercury, gold, platinum, antimony, tin, 
nor arsenic,* are present ; the absence of peroxide of iron 
and of chromic acid is also indicated by this negative re- 
action. 

/>. A frecipitate is formed. 

aa. It is of a pure white colour, thin, in the form of a 
fine powder, and does not vanish on the addition of hydro- 
chloric acid. It consists of sulphur, and indicates per- 
oxide of iRON.t None of the other metals, enumerated 
at § 115, a, can be present. The original solution is 
treated as § 118 directs. 

hb. The precipitate is coloured. 

Solution of sulphuretted hydrogen is added to the largei 
portion of the acid or acidified solution, till the latter has 
acquired the distinct odour of sulphuretted hydrogen, and 
the precipitate no longer increases on the continued 
addition of the reagent; the solution is then heated tc 
boiling, and strongly agitated for some time. 

In many cases, and especially when there is any reason 

* To assure ourselves of the certain absence of arsenic acid, we must allow 
the test solution to stand for some time, or add sulphurous acid, previous to 
the addition of the sulphuretted hydrogen. (Compare § 93, e.) 

f Sulphur is also precipitated in presence of sulphurous acid, iodic acid, 
bromic acid, — which substances we do not treat of in the present work, — and 
also when chromic acid, chloric acid, or free chlorine are present. 


DETECTION OF THE BASES. 


213 


to suppose arsenic to be present, it is better to transmit 
sulphuretted hydrogen gas through the solution. 

1. The PRECIPITATE IS OF A PURE YELLOW COLOUR. In this 
case it cnn consist only of arsenious or arsenic acid, of per- 
oxide of tin, or of oxide of cadmium. The fluid — (which is 
then further to be tested according to § 118) — is separated from 
the precipitate,* and the latter washed and drenched with am- 
monia. 

a. The precipitate is completely redissolved : absence of 
cadmium. Acetic acid is added slightly in excess, to the 
solution, and the precipitate formed is tested for tin and 
arsenic, as § 110, 1 , directs. 

1). A yellow residue remains, even after a further addition 
of ammonia and the application of a moderate heat : cad- 
mium. The solution is filtered, and acetic acid, slightly in 
excess, added to the filtrate. If no precipitate is formed, the 
first precipitate consisted exclusively of sulphuret of cad- 
mium ; but if a precipitate is formed, it denotes the presence 
of peroxide of tin, or arsenic ; this precipitate is tested as 
directed § 1 1 G, 1. 

2. The precipitate is orange- red, or yellow', with a 
shade of orange-colour. It indicates antimony, but may, 
moreover, contain tin — (should it have been present as a per- 
oxide) — arsenic or cadmium ; the precipitate is separated from 
the fluid — (which is tested as § 118 directs) — washed, and a small 
portion of it digested with hydrosulpliurct of ammonia, which con- 
tains sulphur in excess. 

a. It redissolves completely : absence of cadmium. The 
rest of the precipitate is treated as directed § 110,2. 

b. A yellow residue remains, even after a more protracted 
digestion, with a larger quantity of hydrosulphuret of am- 
monia : cadmium. The entire precipitate is then treated in 
the same manner as the specimen, the fluid filtered off from 

* The best method of separating a precipitate from a fluid, is to allow the 
precipitate to settle — (this is, facilitated by heating and agitating) — the fluid 
may then be decanted and the precipitate washed. 


214 


DETECTION OF THE BASES. 


tlio sulphuret of cadmium, and acetic acid in a slight excess 
added to the filtrate ; the precipitate formed is treated as 
§ 110, 2, directs. 

3. The precipitate is of a dark brown or black colour. 
The precipitate is separated from the fluid — (which is then tested 
as § 118 directs) — washed with water, drenched and digested for 
some time, with liydrosulphuret of ammonia, containing sulphur 
in excess.* 

a. The precipitate is completely redissolved in hydrosul- 
phuret of ammonia, or in sulphuret of potassium ; absence 
of cadmium, lead, bismuth, copper, and mercury : § 117 may 
therefore be passed over unnoticed. The solution is diluted, 
and acetic acid added, till an acid reaction becomes manifest ; 
it is then heated to boiling, and the precipitate formed, treated 
as § 1 1 G directs. 

h. It does not dissolve, or at least not completely. The 
fluid is filtered off from the precipitate, and the latter is 
washed, (incase § 115, 3, Ja,) or (in case /3) once more 
digested with liydrosulphuret of ammonia, filtered into the 
first solution, and then washed. The residue is reserved for 
further examination, as directed §117. A small portion of 
the filtrate containing liydrosulphuret of ammonia is diluted 
with from three to four parts of w r ater, acetic acid added, till 
an acid reaction becomes manifest, and the liquid heated to 
boiling. 

«. The fluid simply becomes milky, owing to the sepa- 
ration of sulphur. Absence of gold, platinum, tin, anti- 
mony, and arsenic. Pass over to § 117. 

(5. A coloured precipitate is formed. The colour of 
the precipitate is minutely inspected ; the entire solution 
containing the liydrosulphuret of ammonia is then slightly 

* If the solution contains copper, which may generally be detected by its 
colour, but with certainty by testing with a clean iron rod, (vide § 91, b, 6,)i 
solution of sulphuret of potassium must he substituted for liydrosulphuret I 
of ammonia, and the sulphur precipitate be boiled in it, (i. e. in the sulphuret i 
of potassium,) vide § 91, b, 2. 


DETECTION OF THE BASES. 


215 


diluted, acetic acid added, till an acid reaction becomes 
manifest, and the fluid heated to boiling. 

§ H6. 

The precipitate which acetic acid has produced in the solution 
containing hydrosulphuret of ammonia or sulphuret of potas- 
sium, is 

1. OF A PURE YELLOW COLOUR, WITHOUT THE SLIGHTEST 
shade of orange : arsenic or tin. The solution is filtered 
off from the precipitate, the latter well washed, and together with 
the filter placed between somo sheets of blotting-paper; when 
the paper has imbibed the greater part of the water, the still 
moist precipitate is removed from the filter, and mixed in a small 
porcelain crucible with ubout half its amount of pure anhy- 
drous carbonate of soda, and one and a-half its amount of pure 
nitre ; the mass is then gently heated, and stirred, till it has be- 
come completely dry, when a stronger heat is applied — (beginning 
at the edge of the crucible) — till the entire mass fuses, and every 
particle of the sulphuret is decomposed. (If after drying the mass 
a very high degree of heat is suddenly applied and allowed 
to act upon the whole crucible at once, slight explosions take 
place, whereby more or less of the mass is thrown out of the 
crucible.) 

a. The melting mass is transparent. Absence of tin. The 
mass, after cooling, is boiled with water, the solution divided 
into two portions, and very dilute nitric acid very cautiously 
added to the one, till a feebly acid reaction becomes manifest; 
heat is then applied. (If there is really no tin present, no 
white pulverulent residue must remain, on boiling the defla- 
grated mass with water, neither must any precipitate be 
formed, on acidulating the solution with nitric acid, not even 
after standing at rest for some time.) Nitrate of silver is 
added to the acidified solution, after cooling, and the fluid fil- 
tered ; if any traces of chloride of silver should still separate, 
which is frequently the case if the reagents are not absolutely 


210 


DETECTION OF THE BASES. 


pure, or the precipitate not completely washed. The filtrate 
is then slowly and cautiously covered in a test-tube with very 
dilute ammonia — (one part of ammonia to twenty parts of 
water) — and allowed to stand for some time, without agitat- 
ing. The formation of a reddish brown precipitate, which 
appears like a cloud between the two layers (of the test spe- 
cimen and the dilute ammonia) indicates arsenic ; (this pre- 
cipitato is more clearly seen, on the light falling upon than 
through it.) As a further proof, the second portion of the 
solution of the deflagrated mass is precipitated by solution of 
neutral acetate of lead, the precipitate filtered off, dried be- 
tween some sheets of blotting-paper, and then, on charcoal, 
exposed to the reducing flame of the blow-pipe. If arsenic 
is really present, a grain of metallic lead containing arsenic 
will be obtained, which emits the garlic odour of arsenic very 
long and continuously, as often as it is exposed to the re- 
ducing blow-pipe flame. For further confirmation, the arsenic 
must be obtained in its metallic state. (Compare § 94, d 
and e.) Whether the arsenic was present in the compound 
under examination as arsenic acid, or as arsenious acid, may 
be ascertained according to the method described at the end 
of § 94. 

b. The melting mass is milky and turbid. This is a pro- 
bable indication of the presence of tin. The mass is digested 
with cold water, and rubbed with it in a mortar ; the solution 
is then filtered, and the precipitate which remains, if tin is 
really present, very carefully washed, and then tested for tin, 
by reducing it before the blow-pipe mixed with cyanide of 
potassium and corbonato of soda, and strongly rubbing the 
specimen in a mortar, with the addition of water; vide 
§ 94, b. The liquid filtered off from this precipitate is 
divided into two portions and tested for arsenic as § 1 10, 1, a, 
directs. A slight precipitate generally separates, on acidify- 
ing the solution with nitric acid. This may be filtered off 
and tested for tin in the same manner as the undissolved re- 
sidue, (vide supra.) But if the tin has already been dc- 


DETECTION OF THE BASES. 


217 


tected, this precipitate may be left in the solution, nitrate of 
silver added, filtered, and the fluid tested for arsenic acid, as 
directed above. Whether the tin was present as protoxide, is 
ascertained, by mixing a portion of the original solution in 
water or hydrochloric acid, with a drop of nitric acid and 
some chloride of gold. (§ 94, b, 5.) 

2. Orange-red, or yellow, with a shade of orange ; 
antimony : and besides tin and arsenic may he present. The 
precipitate is washed and fused with nitre and carbonate of soda, 
in short, tested for arsenic and protoxide of tin, exactly as § 1 10, 
1, b, directs. The residue remaining on treating the deflagrated 
mass -with cold water, as well as the precipitato which may per- 
chance be formed on acidifying the solution with nitric acid, may 
be tested in three different ways. 

a. The residue (or precipitate) is most carefully washed, 
mixed with cyanide of potassium and carbonate of soda, and 
exposed, on charcoal, to the reducing flame of the blow- 
pipe. 

o. Metallic globules appear, which at last completely 
volatilize, with the emission of white fumes and the for- 
mation of a white crust. This is confirmatory of the pre- 
sence of ANTIMONY, and of the absence of tin. 

(3. White metallic globules remain, after long blowing : 
tin. Their presence and nature may best be ascertained 
by rubbing the particles of the charcoal surrounding the 
test-specimen, together with the latter, in a mortar with 
some water. (§ 94, b.) 

b. The residue (or precipitate) is very carefully washed 
with water, dried, and fused for some time in a small porce- 
lain crucible, together with from four to five times its amount 
of cyanide of potassium. The mass, after cooling, is drenched 
with water heated to boiling, and thus the dross is separated 
from the metallic globules. These are treated with nitric 
acid, and the operation for the detection of tin and antimony 
conducted exactly as § 100 B, 2, b, directs. 

c. The residue (or precipitate) is well washed, dissolved 


218 


DETECTION OF THE BASES. 


in hydrochloric acid, tlio solution diluted, and a small zinc 
rod placed into it. When the action of the latter has ceased, 
and the reduction is complete, the reduced metals (which 
can he easily separated from the compact piece of zinc,) are 
boiled with nitric acid, and the operation is carried on, ex- 
actly as § IOC B, 2, b, directs. 

The two latter methods of distinguishing tin and antimony 
from each other, when together in the same substance, 
arc, for beginners at least, far safer than the first. 

3. Brownish-black; gold or platinum; besides, perhaps, 
also antimony, arsenic, tin. Add to the original solution of 
the substance 

a. Protochloride of tin ; the formation of a reddish-brown 
or purple-red precipitate denotes gold. We assure ourselves 
of the presence of this metal by testing the original solution 
with protosulphate of iron, whereby metallic gold is precipi- 
tated as a black powder. 

1. Muriate of ammonia ; the formation of a yellow pre- 
cipitate is indicative of the presence of platinum. The 
solution, if highly dilute, should be concentrated by evapo- 
ration, previous to adding this reagent. 

A portion of the precipitate is tested for arsenic, as di- 
rected § 11G, 1. The rest is boiled with hydrochloric acid 
and filtered off; the filtrate is tested for antimony by drop- 
ping one drop of it into water; (after having previously re- 
moved, as much as possible, the excess of acid by evapora- 
ration ;) if the water becomes turbid and milky, antimony is 
present. Or a small portion of the filtrate is mixed with 
solution of sulphuretted hydrogen ; the formation of an 
orange-coloured precipitate indicates antimony. The rest of 
the hydrochloric solution is evaporated to dryness, mixed 
with carbonate of soda and cyanide of potassium, and tested 
for peroxide of tin, as § 110, 2, directs. Antimony and tin 
may, however, more safely be detected by precipitating them 
from the hydrochloric filtrate, by means of zinc ; in fact, by 
treating exactly as § 110, 2, c, directs. 


DETECTION OF THE BASES. 


219 


§ 117. 

The precipitate which has not been dissolved by hydrosulpliuret 

• • • 

of ammonia, is washed, and then boiled with nitric acid. This 
may best be done in a small porcelain basin, constantly stirring 
with a glass rod. 

1. The PRECIPITATE DISSOLVES, AND nothing remains float- 
ing IN THE FLUID EXCEPT THE SEPARATED, LIGHT, FLOCCULENT, 

I yellow sulphur ; this indicates the absence of mercury. Cad- 
mium, copper, lead, and bismuth, may be present. If the pre- 
cipitate was of a pure yellow colour, it consisted of cadmium 
alone ; if it was brown or black, it must bo filtered oft’ from the 
separated sulphur, and the filtrate tested as follows. 

a. Ammonia in excess is added to one portion of the 
^ filtrate. 

a. No precipitate is formed, or the precipitate formed 
at first, redissolves complete/// in an excess of the pre- 
cipitant. Absence of lead and bismuth. The solution 
is treated as § 117, 1, h, directs, bearing in mind § 117, 

I I, a, y. 

ft. A lasting precipitate is formed : lead or bismuth. 
The liquid is filtered off, and the filtrato treated according 
to § 117, 1, b, bearing in mind § 117, 1, a, y. 

y. The fluid is blue-coloured, no matter whether a preci- 
pitate is formed or not ; copper. 

b. Hydrochloric acid is added to the ammoniacal solution 
till a slightly acid reaction becomes manifest ; carbonate of 
ammonia is then added in excess. 

u. The fluid remains clear : absence of cadmium. 
ft. A white precipitate is formed immediately, or after 
applying heat to the solution : cadmium. We assure 
ourselves of tlie presence of this substance by filtering the 
fluid off from the precipitate, wasliing the latter, dissolving 
it in hydrochloric acid, and adding solution of sulphu- 
6 


220 


DETECTION OF THE BASES. 


retted hydrogen. A yellow precipitate must appear, if cad- 
mium is present. 

Should copper not yet have been indicated by a blue 
colouring of the ammoniacal solution, the fluid in which 
carbonate of ammonia has produced no precipitate, (§ 117, 
1, b, a,) or the filtrate of § 117, 1, b, j 3, must be further and 
more minutely examined, by slightly acidifying the one or 
the other with acetic acid, and adding ferrocyanide of potas- 
sium. If copper is present, a brownish-red precipitate or 
tint will be produced. 

c. In the case of § 1 17, 1, a, ft, a not too inconsiderable 
quantity of sulphuric acid is added to a second portion of 
the solution of the sulphurets in nitric acid ; the formation 
of a precipitate is indicative of the presence of lead. This 
reaction may be rendered more obvious and distinct by ex- 
pelling the greater part of the free nitric acid by evapo- 
ration. 

d. The rest of the solution (in the case of § 117, 1, a, ft,) 
is evaporated to dryness, a few drops of water added, and, in 
proportion to the quantity, one or two drops of hydrochloric 
acid, and the fluid heated. The solution is then poured into 
a test-tube containing water ; if the water becomes turbid and 
milky, bismuth is present.* 

2. The precipitate of the sulphurets does not com- 
pletely REDISSOLVE IN THE BOILING NITRIC ACID, AND A PRE- 
CIPITATE REMAINS, BESIDES THE LIGHT FLOCCULENT SULPHUR. 

This indicates peroxide of mercury, with a certain degree of 
probability, (and almost with certainty, if the precipitate is heavy 
and black). The precipitate is allowed to settle, and the fluid 
filtered off from it ; this filtrate must be tested for cadmium, 
copper, lead, and bismuth, by mixing a small portion of it 
with a large volume of solution of sulphuretted hydrogen, and 
if a precipitate is formed, treating the rest of the filtrate as 

* We refer to chapter II. (additions and remarks to § 117) for another 
method of distinguishing cadmium, copper, lead, and bismuth, from each 
other. 


DETECTION OF THE BASES. 


221 


§ 117, 1 , directs. The residuary precipitate is washed, dissolved 
by the addition of a few drops of aqua regia, ammonia added, till 
the solution retains only a feeble acid reaction, and a drop of it 
placed upon a clean copper plate. If mercury is really present, 
a white stain will appear after some time upon the copper sur- 
face, which presents a metallic lustre when rubbed, and disappears 
on heating. Or the solution in aqua regia is, with addition of 
hydrochloric acid, evaporated till nearly dry, diluted with some 
water, and protocldoride of tin added. The formation of a preci- 

I pitate, white at first, but changing into grey on the proto- 
chloride of tin being added in excess, is a safe indication of 
the presence of mercury. 

§ 118. 

A portion of the fluid in which solution of sulphuretted hydro- 
gen has produced no precipitate, (§ 1 15, a,) or of the fluid which 
has been filtered off from the precipitate formed, is mixed with 
ammonia, till an alkaline reaction becomes manifest, and liydro- 
sulphuret of ammonia is then added. 

In cases where but a minute quantity of hydrochloric acid is 
present, and where, therefore, but little muriate of ammonia has 
been formed, a not too inconsiderable measure of a solution of 
this latter salt must be added, previous to the addition of the 
hydrosulphuret of ammonia. 

a. No precipitate is formed. Toss over to § 119, for 
neither iron, manganese, cobalt, zinc, nickel, oxide of 
chromium, nor alumina, are present; neither are the phos- 
phates of the alkaline earths, nor oxalate of lime (barytes, 
strontian). 

1>. A PRECIPITATE is formed. The whole fluid is treated 
in the same manner as the first portion. 

1. The precipitate is white. Absence of iron, cobalt, nickel. 
We must look for the presence of all the other metals and com- 
pounds enumerated at § 118, a, since the faint tints of sulphuret 
of manganese and oxide of chromium vanish altogether if the 


222 


DETECTION OF THE BASES. 


quantity of white precipitate is considerable. The precipitate is 
filtered off — (the filtrate is treated according to § 119) — washed, 
dissolved in hydrochloric acid,* boiled up, the solution filtered, 
and potash in excess added. 

a. The precipitate formed at first on the addition 

OF POTASH, REDISSOLVES COMPLETELY IN THE EXCESS OF 

the precipitant. Absence of the phosphates and oxalates 
of the alkaline earths, and manganese. The solution with 
potash is divided into two portions ; one portion is slightly 
acidified with hydrochloric acid, ammonia in excess added, 
and the fluid boiled for a short time. 

a. No lasting precipitate is formed. Absence of alu- 
mina and of oxide of chromium. Solution of sulphuretted 
hydrogen is added to the other portion of the solution 
with potash. The formation of a white precipitate indi- 
cates zinc. 

/3. A lasting precipitate is formed. It is filtered off, 
and, (should a green tint of the solution with potash, or a 
green, yellow, or a red tint of the original solution make us 
conclude that oxide of chromium is present,) a small 
portion of it tested for this substance, with phosphate of 
soda and ammonia, (§ 87, b, 5,)t solution of sulphuretted 
hydrogen is added to the filtrate. The formation of a 
white precipitate indicates zinc. For alumina we test as 
follows. 

aa. No oxide of chromium has been detected. This 

* If the precipitate is inconsiderable, this may best be done by forcing it 
to the lower part of the filter, by means of a syringe bottle, allowing the water 
to run oft', and adding hydrochloric acid drop by drop. If sulpliuret of zinc 
is present, the solution effected by hydrochloric acid is but incomplete ; 
some nitric acid is added in that case, and beat applied. 

f For even if chromic acid is present, a precipitate of oxide of chromium is 
produced by hydrosulphuret of ammonia, the chromic acid being reduced by 
sulphuretted hydrogen. In such cases, the yellow or red colour of the solu- 
tion changes into a green tint, on the addition of the sulphuretted hydrogen, 
and sulphur separates at the same time. 


DETECTION OF THE BASES. 


223 


is sufficient to prove the presence of alumina. To 
assure ourselves of it, we test the precipitate produced 
by ammonia, before the blow-pipe. (Vide § 87, «, 4.) 

bb. Oxide of chromium has been detected. In this 
case, the second portion of the solution with potash is 
boiled, until the oxide of chromium has completely pre- 
cipitated ; the fluid is then slightly diluted, filtered off 
from the oxide of chromium, slightly acidified with 
hydrochloric acid, and ammonia in excess added. The 
formation of a precipitate indicates alumina. The 
blow-pipe, as in aa, is resorted to as a conclusive test. 
Should the separation of the oxide of chromium from 
the solution with potash not succeed by boiling, as may 
be the case under certain circumstances, the precipitate 
produced by ammonia must bo fused with nitre and car- 
bonate of soda, to remove the chromium. (Vide § 87, 
b, 4.) “ Alumina may have been present as a phosphate, 
and may have precipitated as such. For the way in 
which this may be ascertained, we refer to § 110, 1.” 
b. A PRECIPITATE INSOLUBLE IN POTASH HAS REMAINED. 
The solution is filtered off and the filtrate treated as § 118, 
1, a, directs. The residuary precipitate may consist of 
MANGANESE, “ of the phosphates and oxalates of the alkaline 
earths.” The presence of manganese is indicated by the pre 
cipitate assuming a brown colour when exposed to the air. 
The test with carbonate of soda before the blow-pipe is re- 
sorted to as a conclusive proof. (§ 88, b, 5.) If manganese 
is present, the precipitate is dissolved in hydrochloric acid, 
some tartaric acid mixed with it, and then ammonia in 
excess added. If no precipitate is formed, neither phosphates 
nor oxalates of the alkaline earths are present ; the forma- 
tion of a precipitate indicates the presence of these compounds. 
This precipitate, (or, if no manganese was present, the resi- 
duary precipitate undissolved by potash,) is washed and sub- 
jected to the following preliminary examination, in order to 
ascertain, whether it consists of phosphates of the alkaline 


224 


DETECTION OF THE BASES. 


earths alone or of oxalates of the alkaline earths alone, or 
■whether it is a mixture of both. A small portion of the pre- 
cipitate is gently heated upon a platinum plate, and the 
residue treated with hydrochloric acid. 

a. It dissolves without effervescence : absence of oxalates. 
The rest of the precipitate is then dissolved in hydrochloric 
acid, pcrchloride of iron added in excess, and then ammo- 
nia, and the further operations, for the detection of the 
bases and of the phosphoric acid, conducted as directed 
§ 110, 2, a. 

ft. It dissolves with effervescence : presence of an ox- 
alate. In this case a preliminary examination for phos- 
phates becomes necessary. For this purpose the hydro- 
chloric solution is boiled, to expel the carbonic acid, and 
ammonia added. 

aa. No precipitate is formed. Absence of phos- 
phates : oxalates alone can he present. For the detec- 
tion of the bases, and the confirmatory examination for 
oxalic acid, vide § 110, 2, h. 

bb. A precipitate is formed : presence of a phosphate 
and an oxalate. The rest of the precipitate is then 
heated to redness and dissolved in very slightly diluted 
hydrochloric acid ; the solution is boiled to expel the 
carbonic acid ; ammonia in excess is added, and the 
solution filtered. The earths which were combined with 
the oxalic acid, arc detected in the filtrate, as § 110 
directs. The precipitate is treated as stated § 118, 
1, b. 

2. The precipitate produced by iiydrosulphuret of 
ammonia is not white ; this indicates chromium, manganese, 
iron, cohalt, or nickel. If the precipitate is black or has a shade 
of black, one of the three latter metals is certainly present. But, 
under all circumstances, wo must look for all the metals and 
compounds, enumerated § 118, a. The precipitate is filtered ofi 
from the solution — (the filtrate is treated as § 119 directs) — care- 
fully washed and treated with dilute hydrochloric acid. 


DETECTION OF THE BASES. 


220 


( 1 . No SOLUTION TAKES PLACE, OR THE SOLUTION IS 
INCOMPLETE INASMUCH AS THE BLACK COLOUR OF THE 
PRECIPITATE DOES NOT DISAPPEAR : COBALT, NICKEL. 

Some nitric acid is then added to the hydrochloric acid, and 
the solution boiled and treated as follows. The fluid is 
filtered off from the separated sulphur, and a small portion 
of it mixed with solution of sal ammoniac, ammonia in excess 
added, and heat applied. 

a. No LASTING PRECIPITATE IS FORMED BY AMMONIA : 
absence of peroxide of iron, oxide of chromium, alumina, 
phosphates and oxalates of the alkaline earths. The rest 
of the acid solution of the sulphurets is mixed with caustic 
potash in excess, heated, and the fluid filtered off from the 
precipitate formed. The filtrate is tested for zinc with 
solution of sulphuretted hydrogen. (Compare § 1 1H, 1, a, «.) 
The precipitate is washed and drenched, heated and agi- 
tated for some time with a somewhat considerable quantity of 
solution of carbonate of ammonia, mixed with half its 
measure of caustic ammonia. 

aa. The precipitate is completely redissolved. Ab- 
sence of manganese. The ammoniacal solution is eva- 
porated to dryness, the residue dissolved in a few drops 
of hydrochloric acid, once more slightly evaporated, and 
a portion of a residue — (which should still be moist) — 
tested for cobalt, with borax, (§ 88, d, 7.) The rest 
of the moist residue is then dissolved in some water, and 
solution of cyanide of potassium added, till the preci- 
pitate formed at first, is redissolved in an excess or 
cyanide of potassium ; dilute sulphuric acid is then 
added and heat applied ; the solution is allowed to 
stand for some time. The formation of a greenish 
white precipitate, immediately or after the lapse of some 
time, indicates nickel. (§ 88, c. 0, and lieeapitulation 
and Remarks § 88.) 

lb. An insoluble residue remains, on treating the 
precipitate produced by caustic potash, u ith carbonate 


Q 


220 


DETECTION OF THE BASES. 


of ammonia and caustic ammonia. This is tested for 
MANGANESE, "with carbonate of soda. (§ 88, b. 5.) If 
the precipitate really consists of protoxide of manganese, 
it may almost always safely he detected hy its assuming 
a brown tint, when exposed to the air. The ammoni- 
acal solution is tested for cobalt and nickel, as directed 
§ 118, 2, a, a, aa. 

ft. Ammonia produces a lasting precipitate. The 
entire solution of the sulphurets in aqua regia is then 
treated in the same manner as the first portion, the pre- 
cipitate produced by ammonia, in presence of sal ammoniac, 
is filtered off from the solution and washed ; the further 
operations for testing both the filtrate and precipitate are 
conducted as follow. 

1. Hydrosulphuret of ammonia is added to the filtrate, till 
it causes no longer any precipitation ; the precipitate obtained is 
filtered off from the solution, carefully washed, dissolved in aqua 
regia, mixed with caustic potash in excess and tested for cobalt, 
nickel, manganese, and zinc, exactly as ^ 118, 2, a, a, directs. 

2. The precipitate is digested with dilute solution of potash. 
(If we have obtained only a very minute precipitate, this should 
be dissolved, on the filter, by means of hydrochloric acid, and 
caustic potash in excess added to the solution.) 

aa. The precipitate redissolves completely in the 
caustic potash : absence of peroxide of iron, and of the 
phosphates, and oxalates of the alkaline earths. The 
solution with potash is tested for alumina and oxide of 
chromium, exactly as § 118, 1, a, directs. 

bb. The precipitate does not redissolve, or at least not 
completely. The solution is filtered and the filtrate 
tested for oxide of chromium and alumina, as stated 
at aa. The residue is dissolved in dilute hydro- 
chloric acid, and a small portion of the solution mixed 
with ferrocyanide of potassium. The immediate forma- 
tion of a blue precipitate or even a blue tint in the 
solution indicates iron. If iron is present, the rest of 


DETECTION OF THE BASES. 


227 


the hydrochloric solution is mixed with some tartaric 
acid, and ammonia in excess added. Should no iron 
be present, the solution is simply supersaturated with 
ammonia. If no precipitate is formed, neither phos- 
phates nor oxalates of the alkaline earths are present ; 
if a precipitate is formed, this is treated as § 1 18, 1, b, 
directs. To ascertain whether the iron was present 
as peroxide or protoxide, the original solution in water 
or in hydrochloric acid (but not in nitric acid) is tested 
with ferrocyanide of potassium and with ferricyanide of 
potassium. The formation of a dark blue precipitate 
with the former reagent, indicates peroxide, with the 
latter, protoxide. 

b. The precipitate produced by hydrosulphuret op 
ammonia redissolves readily and completely upon 

BEING TREATED WITH HYDROCHLORIC ACID, OR, AT LEAST, 
ITS BLACK COLOUR DISAPPEARS IMMEDIATELY : absence of 

cobalt and nickel. The solution is boiled with some nitric 
acid, filtered off from the sulphur which precipitates in this 
operation, and a small portion of the filtrate mixed with sal 
ammoniac; ammonia in excess is then added and heat 
applied. 

a. No lusting precipitate is funned upon the addition 
of ammonia : absence of iron, oxide of chromium, alumina, 
phosphates, and oxalates of the alkaline earths. The rest 
of the hydrochloric solution is mixed with potash in ex- 
cess, and the precipitate formed tested for manganese, 
with carbonate of soda ; the alkaline filtrate is tested for 
zinc, with sulphuretted hydrogen. 

ft. A lasting precipitate is formed upon the addition of 
ammonia. The entire solution of the sulplmrets is treated 
in the same manner as the first portion. The precipitate is 
tested exactly as § 118, 2, a, ft, 2 directs. The solution 
which has been filtered oft' from the precipitate, is mixed 
with hydrosulphuret of ammonia in excess. 

Q 2 


228 


DETECTION OF THE BASES. 


oa. No precipitate is formed : absence of manganese 
and zinc. 

bb. A precipitate is formed. This is well washed 
and dissolved in aqua regia, and potash in excess added 
to the solution. 

«a. No lasting precipitate is formed : absence of 
manganese and consequently presence of zinc. For 
further proof sulphuretted hydrogen is added to the 
solution with potash. 

/3/J. A precipitate is formed: manganese. The blow- 
pipe is resorted to as a conclusive test. The fluid 
which has been filtered off from this precipitato 
is treated with sulphuretted hydrogen. The forma- 
tion of a white precipitate indicates zinc. 

§ 119. 

A portion of the fluid in which hydrosulphuret of ammonia has 
produced no precipitate, or which has been filtered off from the 
precipitate formed, is mixed with phosphate of soda and with 
ammonia — (if it does not already contain free ammonia) — and 
strongly agitated. 

a. No precipitate is formed ; this indicates the ab- 
sence of all the alkaline earths. A fresh portion of the fluid 
is evaporated to dryness and the residue heated to redness. 
If no residue remains, (on heating to redness,) neither 
potash nor soda are present : pass over to § 1 22. If a residue 
remains, the entire fluid is treated in the same manner as the 
first portion, and the further operations are conducted as § 
121 directs. 

b. A precipitate is formed. The remainder of the 
fluid, if containing sulphuretted hydrogen or hydrosulphuret 
of ammonia — (in which latter case it must first be acidified 
with hydrochloric acid) — is heated, till it has lost all odour 
of sulphuretted hydrogen, and then filtered off from the 


DETECTION OF THE BASES. 


229 


sulphur, if any lias been precipitated. To tliis filtrate a mix- 
ture of carbonate of ammonia and some caustic ammonia is 
added in excess, — after having previously added muriate of 
ammonia, should this substance not already have been formed 
in the fluid in sufficient quantity during the course of exami- 
nation. The solution is boiled for some time. 

1. No precipitate is formed. Pass over to § 120, neither 
lime, nor barytes, nor strontian being present. 

2. A precipitate is formed : presence of lime, barytes, or 
strontian. The precipitate is filtered off — (the filtrate is tested 
as § 120 directs) — and dissolved in the least possible quantity of 
very dilute hydrochloric acid. 

a. Solution of gypsum is added to a portion of the solu- 
tion. 

a. No precipitate is formed , not even after the 
lapse of some time. Pass over to § 119, 2, b, for 
barytes and strontian are not present. 

1 8 . A precipitate is formed. 

aa. It is formed immediately upon the addition 
of the solution of gypsum : this indicates barytes. 
Strontian may be present besides. 

A portion of the hydrochloric solution (vide § 119, 
2) is evaporated to dryness, and the residue digested 
with absolute alcohol — (at least, with very strong alco- 
hol) — and the solution filtered. A few drops of the 
filtrate are evaporated upon a platinum plate. 

aa. No residue remains. Pass over to 120; for 
neither strontian nor lime are present, 

/3/3. A residue remains. The alcoholic solution is 
divided into two portions : one portion is heated in a 
small crucible and ignited ; a carmine red tint of the 
flame indicates strontian. If the flame does not 
appear red, or if any doubt exists as to its exact tint, 
the second portion of the alcoholic solution is evapo- 
rated to dryness, the residue dissolved in a small 
proportion of water, and the solution tested with 


DETECTION 01' TIIE BASES. 


280 

solution of gypsum. The formation of a precipitate, 
after the lapse of some time, indicates strontian. 

We can best assure ourselves of the presence of 
barytes by adding hydrofluosilicic acid to the solution 
in hydrochloric acid, and applying heat. The for- 
mation of a precipitato after the lapse of some time, 
denotes the presence of barytes. 
bb. The precipitate is formed , only after the lapse 
of some time: absence of barytes; presence of stron- 
tian. 

h. Oxalic acid is added to a fresh portion of the hydro- 
chloric solution, (vide § 119, 2,) after having previously 
made it alkaline by tlio addition of ammonia. Should (after 
§ 1 1 9, 2, a, ft,) barytes or strontian have been detected, 
these must be first precipitated with sulphate of potash, the 
solution filtered off, and the oxalic acid added to the filtrate, 
after the previous addition of ammonia. If a precipitate is 
formed, lime is present. 


§ 120 . 

Two small portions are taken of the fluid, in which carbonate 
of ammonia has produced no precipitate, (§ 119, 1,) or of that, 
which has been filtered off from the precipitate formed, and sul- 
phate of potash is added to the one, oxalate of ammonia to the 
other. 

1. Both these reagents produce no longer any preci- 
pitate. This is a certain proof that all barytes, strontian, and 
lime, have been completely precipitated by carbonate of ammonia, 
rhosphate of soda is added to a third portion of the fluid with 
carbonate of ammonia, and the mixture stirred with a glass rod. 
The formation of a chrystalline precipitate, (vide § 86, d, 5,) in- 
dicates magnesia. The rest of the fluid, a portion of which has 
been tested for magnesia, is evaporated to dryness, and heated till 
all the ammoniacal salts have been expelled. If no residue re- 
mains, pass over to § 122 ; if a residue remains, pass over §121. 


DETECTION OF THE BASES. 


281 


2. Both the reagents, or at least one of them, produce 
still A precipitate. In that case barytes, strontian, and lime, 
have not yet been completely precipitated by carbonate of ammo- 
nia. This reagent, mixed with caustic ammonia, is thereforo 
once more added to the rest of the fluid, and the mixture again 
boiled for some time. The precipitate formed is filtered off from 
the fluid, and again treated as § 120 directs. 

§ 121 . 

We have now still to treat of the examination for fixed alkalies 
and for ammonia. 

The combinations of the former are, with very few exceptions, 
soluble in water. It is therefore not necessary to look for then} 
when testing compounds insoluble in water. 

When we have to operate upon a substance insoluble in water, 
but soluble in hydrochloric acid, or in nitric acid, a portion of the 
fluid, in the specimen of which phosphate of soda did produce no 
precipitate, (§ 119, a ,) — or of that in which carbonate of am- 
monia has occasioned none, (§ 119, 1,) or of that which has been 
filtered of!' from the precipitate formed, (§ 119, 2,)— is preserved 

I and tested for phosphoric acid and oxalic acid, as § 125, 8, 
directs. 

1. Magnesia is not present. The roasted residue of § 119, 
a, is dissolved in a small proportion of water, and alcohol added" 
to the solution ; this is then heated to the boiling point and 
ignited. 

a. The flame has a violet tint. Absence of soda; 
probable presence of potash. 

b. The flame is yellow : presence of soda. The solu- 
tion is evaporated to dryness, and the test with nntimoniato 
of potash, and the blow-pipe flame, are resorted to as con- 
clusive proofs of tbe presence of soda. (Vide § 85, b, 3.) 
We assure ourselves of the presence of potash, by dis- 
solving this residue in water, or, better still, in alcohol, 
if possible, and heating one half of the solution with tartaric 


2fl2 


DETECTION OV THE EASES. 


acid, and tho other half with chloride of platinum. If potash 
ho present, the tartaric acid will produce a colourless, gra- 
nular, crystalline precipitate, after the lapse of some time, 
whilst the chloride of platinum will produce n yellow pre- 
cipitate. 

2. Magnesia is present. The residue is dissolved' in water, 
and water of barytes, or solution of sulphuret of barium (contain- 
ing caustic barytes) added, as long as any precipitate is formed ; 
the solution is then boiled, filtered, and diluto sulphuric acid 
dropped into the filtrate till the reaction has become acid. The 
fluid is then filtered off from the precipitated sulphate of barytes, 
the filtrate evaporated to dryness, and the residue which per- 
chance may remain, tested for potash and soda, as directed 
§121, 1. Or the residue containing magnesia (and perhaps 
alkalies besides) is treated with sulphuric acid, tho solution eva- 
luated to dryness, and the residue heated to redness as long as any 
vapour escapes ; the residuary mass is then dissolved in water, 
and tho solution precipitated by acetate of barytes in excess, 
filtered off from tho precipitate, and the filtrate again evaporated 
to dryness ; the residue is exposed to a strong red heat, and then 
treated with a small proportion of water; the solution is filtered 
and further tested for potash and soda, as § 121, 1, directs. 
Should the filtrate manifest an alkaline reaction, it must first be 
neutralized with hydrochloric acid. 


§ 122 . 

We have now still to consider the examination for ammonia. 
A portion of the substance under examination is treated with con- 
centrated solution of potash, and heat applied. Ammonia is pre- 
sent, if the escaping gas emits its characteristic odour, if it restores 
the blue colour of moist reddened litmus-paper, and if white 
fumes arise upon a small glass rod, moistened with hydrochloric 
acid, being dipped into the tube. 


ABSENCE OF ORGANIC ACIDS. 


233 


Compounds in which all the more frequently occurring aculs and 
bases, metals and metalloids, are supposed to be present. 

A. 1. Substances soluble in water. Detection of acids 

AND METALLOIDS. 

I. Absence of Organic Acids. 

§ 123. 

1 . Concerning the detection of arsenious and arsenic acid, 
CARBONIC ACID, HYDROSULPIIURIC ACID, rtlld CHROMIC ACID, Com- 
pare 108, 1 and 2. 

2. Nitrate of barytes is added to a portion of the solution; if 
the solution is acid, it must first be neutralized with ammonia. 

a. No precipitate is FORMED. Absence of sulphuric 
acid, phosphoric acid, boracic acid, chromic acid, silicic acid, 
oxalic acid, arsenious and arsenic acid.* (Pass over to 3.) 

b. A precipitate is formed. The fluid is diluted, and 
hydrochloric acid added ; if the precipitate does not redis- 
solve, or at least not completely, sulphuric acid is pre- 
sent. 

3. Nitrate of silver is added to a portion of the solution ; this 
is previously exactly neutralized, if acid, by means of ammonia, 
if alkaline, by means of nitric acid. 

a. No precipitate is formed. Pass over to 4 ; neither 
chlorine, nor iodine, cyanogen, phosphoric acid, silicic acid, 
oxalic acid, nor chromic acid are present, nor boracic acid, if 
the solution was not too dilute. 

b. A precipitate is formed. The colour of the preci- 
pitate is inspected, and the nitric acid then added. 

* If muriate of ammonia is present in the fluid under examination, the 
non-formation of a precipitate is not a conclusive proof of the absence of 
oxalic acid, arsenious and arsenic acid, and especially not of that of boracic 
acid, the barytes salts of these acids uot being insoluble in water, in presence 
of ainmoniacal salts. 


28-1 


ABSENCE OJ’ ORGANIC ACIDS. 


a. The precipitate redissolves completely. Fuss over 
to § 123, 4; for neither chlorine, iodine, nor cyanogen 
are present. 

fi. A residue remains : chlorine, iodine, or cyano- 
gen. The residue is washed and digested with am- 
monia. 

aa. A yellowish residue remains. This is caused by 
the presence of iodine. We assure ourselves of the 
presenco of this substance as § 100, c, directs. The 
solution is filtered off from the residue, and nitric acid 
in excess added to the filtrate ; if a precipitate is fonned, 
it indicates chlorine or cyanogen. For the further ope- 
ration, vide hh. 

hh. No residue remains, chlorine or cyanogen ; 
absence of iodine. For further examination, the solu- 
tion is again precipitated with nitric acid. Previous to 
beginning the operation of distinguishing chloride of 
silver from cyanide of silver, the fluid is tested for 
cyanogen, in order to see whether this operation is at 
all necessary. For this purpose solution of magnetio 
oxide of iron is added to a portion of the original 
solution, followed by the addition of hydrochloric acid. 
The formation of a blue precipitate indicates cyano- 
gen.* If no precipitate is formed, and the fluid as- 
sumes no blue tint, the precipitate redissolved by am- 
monia consists of chloride of silver alone. If cyanogen 
has been detected, the precipitate to ho examined is 
washed, taken from the filter when still moist, dried in 
a porcelain crucible, and heated to redness. Chloride 
of silver merely fuses, whilst cyanide of silver becomes 


* Should the cyanogen be present as free hydrocyanic acid, which may 
easily be detected by its characteristic odour, this ought to be saturated with 
potash, previous to the addition of the solution of iron. We have already 
stated at § 100, d, that the cyanogen is not detected by nitrate cf silver, in 
certain combinations, e. g. cyanide of mercury. 


ABSENCE OF ORGANIC ACIDS. 


235 


reduced. The metallic silver may be separated from the 
chloride of silver by means of nitric acid. 

4. The aqueous solution is tested for nitric acid, by mixing 
solution of indigo with it, till it has acquired a light blue tint, 
and then adding some sulphuric acid, and applying heat; and, 
moreover, by throwing a crystal of protosulphate of iron into the 
solution, previously mixed with the third part of its amount of 
concentrated sulphuric acid. If nitric acid is present, the blue 
solution loses its colour, and a brown-coloured halo forms round 
the crystal. 

We have now still to speak of the examinations for phosphoric 
acid, boracic acid, silicic acid, oxalic acid, and chromic acid. It 
is necessary to make these examinations only in such cases where 
chloride of barium, as well as nitrate of silver, have caused the 
formation of precipitates in neutral solutions. Compare note to 
§ 123, 2, a. 

3. If the precipitate produced by nitrate of silver was of a 
yellowish colour, we must especially look for phosphoric acid. 
For this purpose, ammonia in excess is added to a portion of the 
fluid ; if a precipitate is formed, the fluid is filtered, and muriate 
of ammonia added to the filtrate, and then sulphate of magnesia. 
The formation of a crystalline precipitate denotes pnosrHORic 

ACID. 

6. A small portion of the substance under examination is 
drenched with alcohol, sulphuric acid added, and the mixture 
heated to boiling in a small crucible, and then ignited. If the 
flame has a green tint, boracic acid is present. If copper is 
present, this must first be removed, either by means of sulphu- 
retted hydrogen, or by boiling the fluid with potash in excess. 

7. If the fluid was red, or yellow changing to red, on the addi- 
tion of hydrochloric acid, and if the precipitate produced by 
nitrate of silver in the neutral solution had a purple red colour, 
the presence of chromic acid is confirmed. 

8. For silicic acid, test as § 99, b, 2, directs. 

9. For the detection of oxalic acid, solution of gypsum is 
added to a portion of the fluid under examination, which must 


PRESENCE OF ORGANIC ACIDS. 


230 

first be neutralized with ammonia, if it manifests an acid reaction. 
The formation of a white precipitate, which does not vanish upon 
the addition of acetic acid, indicates the presence of oxalic acid. 

Chlorates, bromides, and fluorides, are of less frequent oc- 
currence. Chlorates may be detected by their violent deflagration 
with charcoal, when in a state of fusion. (Vide § 105, A. I. 2, c.) 
Chloric acid is best detected, by heating a portion of the solid 
salt in a glass tube, closed at the lower end, and placing a wood- 
splinter, which has been kindled and the flame extinguished, near 
the open end. If chloric acid be present, the flame of the wood- 
splinter will be rekindled. The residue dissolved in water yields 
in that case with nitrate of silver a copious precipitate of chloride 
of silver. Other tests are, to throw a few grains of the salt into 
fuming sulphuric acid, (§ 101, b. G,) or fusing a portion of the 
salt with cyanide of potassium. (§ 101, b, 3.) The detection of 
bromides is simple, if iodides are not present, at the same time. 
Vide § 100, for the safe detection of bromine in both cases. For 
the detection of the fluorides, the methods described § 08, d, 4 
and 5, are the safest under all circumstances. 


Compounds in which all the more frequently occurring acids and 
bases, metals and metalloids, are supposed to be presen t. 

A. 1. Substances soluble in water. Detection of acids 

AND METALLOIDS. 

II. Presence of Organic Acids. 

§ 124. 

1. Chromic acid, arsenious, and arsenic acid, have already 
been detected when testing for the bases ; concerning the distinc- 
tion of arsenious from arsenic acid, compare § 93, additions and 
remarks. 

2. Hydrochloric acid is added to a portion of the solution. 
The formation of a precipitate, which upon being heated on a 


PRESENCE OF ORGANIC ACIDS. 


237 


platinum plate volatilizes partly or totally, emitting the charac- 
teristic odour of benzoic acid, indicates the presence of this acid. 
Effervescence, upon the addition of the hydrochloric acid, may he 
caused by the presence of carbonic acid, or by that of sulphu- 
retted hydrogen. (Vide § 108, 2.) 

3. Ammonia is added to a portion of the solution, till the latter 
manifests a feebly alkaline reaction ; the solution is then filtered, 
if necessary, and chloride of barium added. 

Should hydrochloric acid have produced a precipitate in 
the original solution, the filtrate of this ought to be used for 
this experiment. 

a. No precipitate is formed. Absence of sulphuric acid, 
phosphoric acid, chromic acid, boracie acid, arsenic acid, arseni- 
ous acid, silicic acid, oxalic acid, tartaric acid, citric acid ; these 
may therefore be disregarded in the further course of exami- 
nation. What we have stated at § 123, 2, a, (note,) ap- 
plies also to the last six of these acids. 

b. A precipitate is formed. Hydrochloric acid is 
added. 

a. The precipitate red is so Ives : Absence of sulphuric 
acid. 

ft. A residue remains : sulphuric acid. 

4. Nitrate of silver is added to a portion of the solution, which 
must first be exactly neutralized with nitric acid, if alkaline, and 
with ammonia, if acid. 

a. No precipitate is formed : absence of phosphoric acid, 
boracic acid, chromic acid, silicic acid, oxalic acid, tartaric 
acid, citric acid ; these may therefore be disregarded in the 
further course of examination. 

b. A precipitate is formed. 

a. It is whitish or yellow. A portion of the fluid, toge- 
ther with the precipitate suspended therein, is boiled. 
Complete and rapid reduction indicates formic acid. 
Protonitrate of mercury is used as a conclusive test, § 1 04, b, 
bearing in mind the remarks which will be found at the 


238 


PRESENCE OF ORGANIC ACIDS. 


end of this number, (4.') The rest of the precipitate is 
treated with nitric acid. If it is redissolved, neither chlo- 
rine, nor iodine, nor CYANOGEN, are present; but if the 
precipitate does not completely rcdissolvc in nitric acid, 
the residue is tested for these salt radicals, as § 123, 3, b, ft, 
directs. 

ft. The precipitate produced by nitrate of silver is 
purple: chromic acid. Should arsenic acid be present, 
acetate of lead is added, or (as a conclusive test, to a fresh 
portion of the solution) the formation of a yellow pre- 
cipitate proves the presence of chromic acid. Chlorine, 
iodine, and cyanogen, may also bo present in the silver 
precipitate: test for these salt radicals as § 123, 3, b, directs. 

In the presence of chromic acid, formic acid cannot bo 
detected with certainty, by the reduction of silver and 
mercury. In this case there remains no other means of 
its certain detection, except distilling the compound under 
examination, with the addition of some sulphuric acid. 
The distillate is saturated with soda, and then tested with 
perchloride of iron, (which chromic acid tinges blood- 
red,) and with nitrate of silver. (Compare § 104, b.) 

5. If chloride of barium and nitrato of silver have given rise to 
the formation of precipitates, test for phosphoric acid, ns directed 
§ 123, 5, and for silicic acid as directed § 99, b, 2. 

0. A portion of the solid substance under examination (or, if 
in solution — (should the latter be acid, it must first be saturated 
with potash) — the residue obtained by evaporating the solution to 
dryness) is drenched with alcohol in a small tube, concentrated 
sulphuric acid to the extent of about one-tliird of the volume 
of the alcohol, and the mixture heated to the boiling point. If 
any odour of acetic ether is emitted — which, in many instances, 
may be clearly detected upon agitating the mixture, whilst cooling 
or when cold — acetic acid is present. The contents of the tube 
are poured into a small crucible, heated, and ignited. If the 
flame is green, boracic acid is present. 

7. A portion of the fluid is rendered feebly alkaline by the ad- 


PRESENCE OF ORGANIC ACIDS. 


239 


dition of ammonia, filtered, if necessary, and chloride of calcium 
added. If the solution was neutral, some sal ammoniac must he 
added before the addition of chloride of calcium. 

a. No PRECIPITATE IS FORMED, NOT EVEN AFTER THE 

lapse of some time. Absence of oxalic acid and tartaric 
acid ; pass over to 8. 

b. A PRECIPITATE IS FORMED IMMEDIATELY, OR AFTER 

the lapse of a few mindtes. The solution is filtered off 
from this precipitate, and the filtrate further tested as 8 
directs. 

The precipitate is washed, digested, and agitated with 
somewhat dilute solution of potash in excess, without the aid 
of heat, filtered, and the filtrate boiled for some time. If a 
precipitate is formed which disappears again, on cooling, tar- 
taric acid is present. 

Solution of gypsum is added to a portion of the original 
solution, which, if acid, must first he made neutral by the 
addition of ammonia. The formation of a precipitate, 
which does not disappear upon the addition of acetic acid, 
hut is dissolved by hydrochloric acid, indicates oxalic acid. 

8. The fluid in which chloride of calcium has produced no pre- 
cipitate, or that which has been filtered off from the precipitate 
formed — (in which latter case some more chloride of calcium is 
added) — is mixed with alcohol. 

a. No precipitate is formed. Absence of citric acid 
and of malic acid. Pass over to 9. 

b. A precipitate is formed. The solution is filtered off 
and the filtrate treated as 9 directs. The precipitate is 
washed with alcohol, and (being left on the filter) dissolved 
in the least possible quantity of dilute hydrochloric acid. 
Ammonia is then added to this latter filtrate, till it manifests a 
feebly alkaline reaction, and heat applied to the boiling point, 
at which it must be kept for some time. 

a. The filtrate remains clear. Absence of citric 

acid. Presence of malic acid ; alcohol is again added to 

the fluid, and the lime precipitate which is formed, heated 


240 


ABSENCE OF ORGANIC ACIDS. 


to redness, ns a conclusive test for malic acid ; the reaction 
with acetate of lead is moreover resorted to as a confirma- 
tory proof, § 102, e, 5. 

ft. A heavy, white precipitate is formed. Presence 
of citric acid. The solution is filtered whilst boiling, 
and the filtrate tested for malic acid, as described at a. 

9. Percldorido of iron is added to the filtrate of 8, b, or to the 
fluid, in which no precipitate has been formed, on mixing with 
alcohol, (§ 128, 8, a,) after having previously expelled the alcohol 
by heat, and after having exactly neutralized with hydrochloric 
acid. If no light brown flocculent precipitate is formed, neither 
succinic acid nor benzoic acid are present ; if a precipitate of this 
kind is formed, and no benzoic acid has been detected during the 
previous examination, (§ 124, 2,) this consists of succinic acid. 
But if benzoic acid was present, the solution is filtered oft', and the 
precipitate washed and then digested with ammonia in excess, fil- 
tered, the filtrate evaporated to dryness, and the benzoate of am- 
monia dissolved out of it by alcohol ; the succinate of ammo- 
nia remains undissolved. This succinate is dissolved in water, 
and both solutions are tested with perchloridc of iron. 

10. Test for nitric acid as directed § 123. 


Compounds in which nil the more frequently occurring bases, 
acids, metals, and metalloids, are supposed to be present. 

A. 2. Substances insoluble in water, but soluble in 

HYDROCHLORIC ACID AND IN NITRIC ACID. DETECTION OF THE 
ACIDS AND METALLOIDS. 

I. Absence of Organic Acids. 

§ 125. 

In examining those compounds we must look for all the acids 
occurring at § 123, with the exception of chloric acid. Cyanogen 
compounds are not examined after this method : compare § 128. 


ABSENCE OF ORGANIC ACIDS. 


2 11 




1. What wc have stated at § 111, 2, with regard to arsenious 
and arsenic acid, hydrosulphuric acid and chromic acid, ap- 
plies also to this paragraph. 

2. A portion of the substance is boiled with nitric acid, and the 
solution filtered, should any residue remain. 

a. Effervescence takes place ; this may be caused by the 
presence of carbonic acid, or by that of nitric oxide gas ; 
the former may be detected as § 99, a, directs, the latter usu- 
ally indicates the presence of a sulphur compound. 

b. Violet vapours escape, which impart a blue tint to 
starch : iodine. 

3. Nitrate of silver is added to a portion of the nitric solution. 

a. No PRECiriTATE is formed : pass over to 4, for no 
chlorine is present. 

b. A precipitate is formed. The solution is filtered off, 
and the precipitate washed, and digested with ammonia ; if it 
redissolves completely or partly, chlorine is present. 

4. A portion of the substance under examination is boiled with 
hydrochloric acid, and the solution filtered, if necessary. A por- 
tion of the solution or filtrate is mixed with chloride of barium. 
The formation of a precipitate indicates sulphuric acid. 

5. Another portion of the hydrochloric solution is tested for 
•nitric acid, with indigo aod protosulphate of iron. (Vido § 

123, 4.) Iu many cases it will already have been detected by the 
deflagration on charcoal before the blow -pipe. 

6. If the experiment, § 125, 2, b, has not yet indicated the pre- 
sence of iodine, a portion of the substance under examination is 
heated with concentrated sulphuric acid. If any iodine compound 
be present, violet vapours will be evolved, which impart a blue 
tint to starch. (Compare § 100, c, G.) 

7. Test for boracic acid by treating a portion of the substance 
to be examined with sulphuric acid and alcohol. (Vido § 98, 
A, 5.) 

8. The fluid of § 119, a, (in which phosphate of soda produces 
no precipitate,) or that of § 119. 1, (in winch carbonate of am- 
monia produces no precipitate,) or— (should carbonate of ammonia 




242 


PRESENCE OF ORGANIC ACIDS. 


havo produced a precipitate in it) — the filtrate of the same (§ no, 
2,) (vide § 121,) are tested for phosphoric acid and oxalic acid, 
as directed § 123, 6, and 0. (Oxalic acid, when combined with 
barytes, strontian, or lime, will have been detected already, in 
testing for the bases ; the same applies to phosphoric acid when 
combined with magnesia.) 

9. Test for silicic acid as § 99, b, 3, directs. With regard to 
the more rarely occurring bromine and fluorine compounds, we 
refer to the remarks made at the end of § 123. 


Compounds in which all the more frequently occurring bases, 
acids, metals, and metalloids, are supposed to be present. 

A. 2. Substances insoluble in water, but soluble in 

hydrochloric acid, and in nitric acid. Detection of 

THE ACIDS AND METALLOIDS. 

II. Presence of Organic Acids. 

§ 120 . 

1. Test for carbonic acid, arsenic acid, arsenious acid, 

SULPHURIC ACID, NITRIC ACID, BORACIC ACID, CHROMIC ACID, 
silicic acid, chlorine, iodine, and sulphur, as directed at 
§ 125 ; for acetic acid as stated at § 124, G. Cyanogen com- 
pounds are not examined after this method : compare § 128. 

2. A portion of the compound under examination is dissolved 
in hydrochloric acid, and the solution filtered, should any residue 
remain, (which latter is tested for benzoic acid, as directed at 
§ 124, 2.) The filtrate is mixed with solution of carbonate of 
potash, and the mixture boiled for some time. The fiuid is fil- 
tered off from the precipitate formed, and the filtrate saturated 
with dilute hydrochloric acid, and tested for phosphoric acid and 
oxalic acid, as directed at § 123, 5, and 9; and for tartaric 
acid, citric acid, malic acid, succinic acid, and benzoic acid, 
exactly as directed at § 124, 7, 8, and 9. 


INSOLUBLE SUBSTANCES. 


243 


Compounds in which all the more frequently occurring bases, 

acids, metals , and metalloids, are supposed to be present. 

B. Substances insoluble or sparingly soluble both in 

WATER AND IN HYDROCHLORIC ACID. DETECTION OF THE 

BASES, ACIDS, AND METALLOIDS. 

§ 127. 

The following substances and combinations belong to this 
class : 

Sulphate of barytes, sulphate of strontian, sulphate 
of lime, chloride of silver, chloride of lead, sulphate 

OF LEAD, SULPIIURET OF MERCURY, BISULPHURET OF MERCURY, 
PROTOCIILORIDE OF MERCURY', SOME OF THE FERROCY'ANIDES, 
SEVERAL SULPHURETS, SILICIC ACID, SULPHUR, and CARBON. 

Besides these, a few acid arseniates belong to this class ; they 
are, however, as rarely occurring in the analyses of those mixtures 
and compounds important in pharmacy, manufacture, arts, and 
trades, as the insoluble modification of oxide of chromium, or as 
roasted peroxide of tin, or as fluoride of calcium. Of these latter 
less frequently occurring substances, we purpose to treat sepa- 
rately. 

For the insoluble cyanides, vide § 128. 

A. The residue is white. It may in that case contain 
SULPHATE OF BARYTES, SULPHATE OF STRONTIAN, SULPHATE OF 
LIME, SULPHATE OF LEAD, CHLORIDE OF LEAD, CHLORIDE OF 
SILVER, PROTOCHLORIDE OF MERCURY’, SILICIC ACID, SULPHUR. 

No attention need be paid to the presence of sulphate of lime, 
if this substance has already been detected in the aqueous solu- 
tion. The same remark applies to the lead compounds : we may 
disregard these, if the previous examination has not already proved 
their presence. 

1. A small portion of the substance under examination is heated 
upon a platinum plate, and flame allowed to play on it. If 

R 2 


241 


PRESENCE OF ORGANIC ACIDS. 


tiny odour of sulphurous acid is emitted, sulphur is present. If 
no residue remains, sulphur alone is present. If the heat applied 
was very intense, protochloride of mercury may have volatilized. 
The sensible properties of the residue will show whether this is to 
he apprehended. 

2. Hydrosulphuret of ammonia is added to a very small portion 
of the substance under examination. 

a. It remains white. Pass over to § 1 27, 3, for no me- 
tallic compounds arc present. 

h. It becomes black. This proves with certainty the pre- 
sence of a metallic salt, either protochloride of mercury, 
chloride of silver, chloride of lead, or sulphate of lead. 
Moreover, all the other compounds enumerated under A, may 
ho present. The method of the further operation varies ac- 
cording to whether lead is present or not. 

The following preliminary experiment is made in order to 
ascertain which method ought to be adopted. 

A small portion of the substance is mixed with carbonate 
of soda, and exposed to the reducing flame of the blow-pipe. 
The production of a metallic grain, (which oxidizes in the 
oxidizing flame,) attended with a yellow incrustation of the 
charcoal, indicates lead. 

«. This preliminary examination indicates the 

PRESENCE OF LEAD IN THE WHITE PRECIPITATE. 

a a. The largest half of the residue (which, if moist, 
must first he dried) is fused with three parts of dry 
carbonate of soda and three parts of cyanide of potas- 
sium, in a small crucible, over a spirit-lamp. The mass 
fuses easily ; it is maintained in a state of fusion for 
some time. After cooling, it is boiled with water, fil- 
tered, and the residue very carefully washed. The 
greater portion of the filtrate is supersaturated with 
hydrochloric acid, and a portion of this solution tested 
with chloride of barium. The formation of a precipitate 
indicates the presence of a sulphate. (Should a pre- 
cipitate (silicic acid) be formed, upon supersaturating 


INSOLUBLE SUBSTANCES. 


240 


the filtrate with hydrochloric acid, the fluid must be di- 
luted and filtered, and then tested for sulphuric acid.) 
The rest of the solution (supersaturated with hydro- 
chloric acid) is evaporated to dryness, and the residuo 
treated with water. If a residue remains, this consists 
of silicic acid. The formation of a clear glass, when 
fused with carbonate of soda in the blow-pipe flame, is a 
conclusive proof of the presence of silicic acid. The 
rest of the filtrate, which has not been mixed with hydro- 
chloric acid, is acidified with nitric acid, boiled until it 
emits no longer any odour of hydrochloric acid, and 
nitrate of silver added ; the formation of a precipitate of 
chloride of silver denotes that the residue, insoluble in 
water and hydrochloric acid, contains a chloride, (pro- 
vided always, the reagents be free from chlorine, and the 
residue completely washed.) The residue obtained upon 
treating the fused mass with water, and which has been 
very carefully washed, (vide supra,) is treated with acetic 
acid ; if it partly dissolves in this acid with effervescence, 
the presence of sulphates of the alkaline earths is cer- 
tain. If no effervescence takes place, it proves the ab- 
sence of the sulphates of the alkaline earths ; the residue 
is therefore treated with nitric acid, and the solution 
treated as follows. If effervescence has taken place, a 
portion of the acetic solution is tested with sulphuretted 
hydrogen. If a black precipitate is formed, (sulplniret 
of lead,) the lead is removed in the same manner from 
the entire acetic solution, and the filtrate (which, if ne- 
cessary, is concentrated by evaporation) treated as 
§119 directs, beginning at 2, a. If the test portion of 
the acetic solution remains unaltered upon being treated 
with sulphuretted hydrogen, the rest of the solution is 
directly tested as directed. § 119, 2, a. The residue, 
which lias remained on treating with the acetic acid, is 
treated with nitric acid, and a small portion of the solu- 


PRESENCE OF ORGANIC ACIDS. 


tion is then tested with sulphuric ftcid for lend, (after 
having removed the excess of acid by evaporation ;) the 
rest strongly diluted with water, and then tested for 
silver, with hydrochloric acid. If nitric acid leaves a 
residue, this consists of undissolved silicic acid, or incom- 
pletely decomposed sulphate of the alkaline earths. 

bb. Half of the remainder of the residue is boiled 
with carbonate of potash. If its white colour change 
into grey or black, protochloride of mercury is pre- 
sent. As a confirmatory test, the other half is heated in 
a small glass tube, together with dry carbonate of soda. 
(Vide § 90, b, 7.) 

ft. The preliminary examination proves the ab- 
sence of lead, in the white precipitate. The entire 
residue is drenched and digested for some time, with liydro- 
sulphuret of ammonia, the solution filtered, and the filtrate 
tested for chlorine, as aa directs. The precipitate is 
washed, and boiled with nitric acid. 

aa. The precipitate dissolves, with the exception oj 
the separated sulphur. Chloride of silver alone is 
present. To assure ourselves, we test the nitric solutior 
for silver, with hydrochloric acid. To prove the pre 
sence of chlorine, the filtrate of § 127, A, 2, ft, is super 
saturated with nitric acid, and boiled in order to expel 
the sulphuretted hydrogen ; the fluid is then filtered from 
the sulphur which lias separated, and tested with nitrate 
of silver. 

bb. A residue remains, besides the separated sulphur. 

aa. This residue is black : mercury. The fluid 
is filtered from the residue, and the filtrato tested for 
silver, with hydrochloric acid ; the residue is heated 
with aqua regia. If it is completely rcdissolved, with 
tho exception of tho separated sulphur, the investi- 
gation may be considered at an end, the absence of 
the sulphates of the alkaline earths and that of silicic 


INSOLUBLE SUBSTANCES. 


247 


acid being proved ; if a white residue remains, this 
is washed and treated as § 127, A, 3, directs. The 
solution in aqua regia is tested with polished copper 
or with protocldoride of tin to assure ourselves of the 
presence of mercury, (vide § 117, 2.) The chlorine, 
which must he present, is detected in the filtrate of (3, 
as aa directs. 

/3/3. The residue is not black : absence of mer- 
cm - }\ For the further operation vide 3. 

3. This residue, or, in the case of § 127, A, 2, a, the original 
residue, is fused in a platinum crucible,* over a spirit lamp with a 
double draught of air, together with four parts of carbonate of 
potash and soda ; the fused mass is soaked in water, boiled, 
filtered, and the residue (if any remain) washed until chloride of 
barium no longer produces any precipitate in the water which 
runs off. (This water must not be added to the filtrate.) The 
residue is treated as 4 directs. The filtrate is supersaturated with 
hydrochloric acid, and a portion of it tested with chloride of 
barium ; the formation of a precipitate indicates the piesence of 
sulphates OF the alkaline earths. The rest of the filtrate 
is evaporated to dryness and then treated with water ; if any 
residue remains, this consists of silicic acid. 

4. The residue remaining upon boiling the fused mass with 
water, (vido 3,) indicates sulphates of the alkaline earths. 
It is carefully washed and then treated with hydrochloric acid. 
It is a certain proof of the presence of sulphates of the alkaline 
earths, if it dissolves partly or totally, and with effervescence in 
this menstruum. The hydrochloric solution is tested as § 119 
directs, beginning at 2, a. If a residue remains upon treating 
with hydrochloric acid, this consists of silicic acid or of a sulphate 
of the alkaline earths which is not yet completely decomposed. 

B. The residue is not white. Even its colour will in 

* A porcelain crucible may be substituted for a platinum crucible, in 
which case, six parts of a mixture of equal parts of dry carbonate of soda and 
cyanide of potassium must be employed, instead of the carbonate of potash 
and soda; the method in the text is however the best. 


PRESENCE OF ORGANIC ACIDS. 


248 

that case enable us to draw somo conclusions (cinnabar, sul- 
phuret of arsenic) . 

1. Test for sulphur as § 127, A, 1, directs. 

2. The greater part of the residue is treated with aqua regia and 
boiled ; the solution is filtered whilst still hot, and should any 
residue remain, besides the separated sulphur, this is once more 
boiled with water, filtered, and this second filtrate added to the 
first. The filtrate is then evaporated nearly to dryness, redis- 
solvcd in somo water, and one portion of the solution tested for 
lead, with sulphuric acid, another portion for mercury by means 
of polished copper. (If a hydrochloric solution has been em- 
ployed in testing for bases, (§ 100,) the solution in aqua regia 
must be tested for metals, in the usual way, as various other sul- 
pliurets, insoluble or sparingly soluble in hydrochloric acid, might 
bo present.) 

8. If aqua regia has left any residue undissolved besides sul- 
phur, which may have separated, this residue is carefully washed 
If a compound of lead lias been present, this rinsing process is 
conducted with hot water and continued until the filtrate is no 
longer blackened by hydrosulphuret of ammonia. 

a. The residue is white : a portion of it is tested with 
hydrosulphuret of ammonia. 

a. It becomes black. The entire residue is digested 
with hydrosulphuret of ammonia, and the further opera- 
tion conducted exactly as § 127, A, 2, b, ft, directs. 

/3. It remains white. The residue is treated as directed 
§ 127, A, 3. 

b. The residue insoluble in aqua regia, is black ; 
this indicates the presence of carbon in sonic form. If it is 
totally consumed over a lamp, or in the blow-pipe flame^ 
nothing besides carbon is present; but if a residue remains, 
or if the combustion is not complete (carburet of iron, 
graphyte,) w T e must look moreover for chloride of silver, 
sulphates of the alkaline earths and silicic acid ; 
the residue in that case, is treated as § 127, B, 3, a , a, 
directs. Of acids aud electro-negative substances chlorine 


METHOD WITH INSOLUBLE CYANIDES. 


*249 


and sulphuric acid alone can be present besides those 
already mentioned. To assure ourselves whether they are 
present or not, what remains of the residue insoluble in 
hydrochloric acid is digested with hydrosulphuret of ammo- 
nia, super- saturated, filtered, and one-half of the filtrate 
boiled with hydrochloric acid, the other half with nitric acid ; 
both solutions are filtered and the hydrochloric fluid is 
tested with chloride of barium for sulphuric acid, the nitric 
fluid with nitrate of silver for chlorine. 

The insoluble peroxide of tin and oxide of chromium 
may be detected before the blow-pipe. Peroxide of tin, 
when mixed with carbonate of soda and cyanide of potassium, 
and exposed on charcoal to the reducing flame of the blow- 
pipe, yields a soft metallic grain, without incrustation of the 
support. Oxide of chromium, which is moreover distin- 
guished by its green colour, is treated with microcosmic salt, 
as stated § 87, b, 5, or it is fused together with carbonate of 
soda and nitre, (vide § 87, b, 4.) The arsenic acid of the 
insoluble arseniates is detected before the blow-pipe or by 
means of reduction in a glass tube. (Tide § 94, d.) To enable 
us to test for the bases, these insoluble arseniates must first 
be decomposed by means of concentrated sulphuric acid. 
Fluoride of calcium is decomposed by concentrated 
sulphuric acid, in a platinum crucible : the fluorine is de- 
tected by its property of etching glass ; the lime remains as 
sulphate of lime. There are still several other compounds 
which are rendered insoluble in acids by being heated to red- 
ness ; but it would exceed the limits of this work, to treat of 
them all. 


§ 128. 

SPECIAL METHOD FOR THE DECOMPOSITION OF INSOLUBLE 
CYANIDES, FERROCYANIDES, &C.* 

* The student is advised to read the additional remarks to § 128 , contained 
the second chapter, previous to entering upon this method of analysis. 


250 


METHOD WITH INSOLUBLE CYANIDES. 


Since in treating these compounds according to the usual 
method, fallacious phenomena frequently occur, and since more- 
over their solution in acids frequently succeeds hut imperfectly, 
it is advisable to pursue the following method, in their analysis. 
The residue which has been freed by water from all solublo sub- 
stances, is boiled with solution of carbonate of potash. 

a . Complete decomposition takes place, which is 
easily detected by tlio change of colour and the rapid depo- 
sition of the separated pure or carbonated oxides ; the solu- 
tion is filtered and the residue washed. This residue may 
contain all the bases, which were contained in the substance 
under examination as compounds insoluble in water. For 
the determination of these bases, the residue is treated exactly 
as § 1 00, A, 2, directs. A portion of the filtrate is tested for 
cyanogen, by mixing it with hydrochloric acid, till the 
reaction becomes strongly acid, and then adding solution of 
the double proto- and per-chloride of iron ; if cyanogen be 
present, Prussian blue precipitates. For the detection of the 
other acids, the rest of the filtrate is treated as § 124 
directs. This filtrate may moreover possibly contain all the 
cobalt, all the iron of the substance under examination, 
besides chromium and manganese, since the combinations of 
their cyanides with other cyanogen compounds, on boiling 
with alkalies, are decomposed in such a manner as to cause 
the separation of insoluble oxides, whilst the cobalticyanide 
of potassium, fcrrocyanide of potassium, &c., remain in solu- 
tion. These metals must not bo disregarded. To detect 
them, a portion of the fluid is mixed with nitric acid greatly 
in excess, the mixture evaporated to dryness and the residue 
fused ; should the quantity of the nitre formed not be suffi- 
cient, some must be added whilst fusing the residue. The 
metals, with the exception of chromium, remain as oxides, 
and are separated and detected according to the methods 
given above. The chromium is obtained as soluble chromate 
of potash. 

h. No complete decomposition takes place: caustic 

6 


PRESENCE OF ORGANIC MATTER. 


251 


potasli is added and tlio mixture boiled. Should any residue 
remain, this is filtered, after the previous addition of some 
water, and then dissolved and treated as § 106, A, 2, directs. 
The alkaline filtrate is saturated with sulphuretted hydrogen. 
If any precipitate he formed, this is again filtered, dissolved 
in nitric acid, and the solution treated as § 114, III. directs. 
The filtrated liquid is slightly acidified with hydrochloric 
acid and sulphuretted hydrogen added should it appear 
nesessary. If a precipitate he formed, this is treated as § 
116 directs. The filtrate is tested for cyanogen and the 
other electro-negative bodies, and acids, and for cohalt, 
iron, manganese, and chromium, as § 128, a, directs. (When 
fusing the residue with nitre, according to the method laid 
down in § 128, a, (vide this section from the words, “These 
metals must not he disregarded,” to the end,) besides the 
oxides, alumina is obtained, if imy he present ; this must he 
borne in mind.) 


§ 129. 

GENERAL RULES FOR THE DETECTION OF INORGANIC SUB- 
STANCES ; IN CASES WHERE ORGANIC SUBSTANCES ARE PRESENT, 
WHICH BY THEIR COLOUR, CONSISTENCE, OR OTHER PROPER- 
TIES, IMPEDE THE APPLICATION OF THE REAGENTS, OR RENDER 
THE PHENOMENA OBSCURE. 

We have already stated in our introductory remarks, that cases 
of this kind are so manifold, that it is impossible to lay down a 
determinate method for every especial case ; we must therefore 
content ourselves with giving only such methods as are applicable 
in most cases, and leaving it to the judgment of the operator to 
adopt those modifications which he may deem necessary. 

1. The substance dissolves in water, but is of a dark 

COLOUR OR HAS A SLIMY CONSISTENCE. 

a. One part of the solution is boiled with hydrochloric 
acid, and chlorate of potash gradually added till the fluid 
has become discoloured and limpid ; the solution is then 


CONFIRMATORY EXPERIMENTS. 


2 52 


heated until all odour of chlorine has disappeared, diluted 
with water, and filtered. The filtrate is treated after the 
usual method, beginning at § 115°. 

b. Another portion of the solution is boiled for some time 
with nitric acid, filtered, and the filtrate tested for silver, 
potash, and hydrochloric acid. This kind of treatment is 
frequently preferable to all others in such cases where the 
destruction of the colouring, slimy matters, &c., succeeds 
well by means of nitric acid. 

2. The body does not dissolve in boiling water , or dissolves only 
m part. The solution is filtered, and the filtrate treated either as 
§ 114 directs, or, if it be necessary to destroy the colouring 
matters which it may contain in admixture, as directed § 129, 1. 
If it is impossible to filter the solution, the further operation must 
be conducted as stated § 129, 2, c. The nature of the residue 
may be various. 

a. It is greasy. The fatty matters are removed by 
means of ether, and should any residue remain, this is treated 
as § 100 directs. 

b. It is resinous. Alcohol is employed instead of ether, 
or a mixture of both liquids is used. 

c. It is of another nature, e. g. organic fibrinc, &c. 
The residue insoluble in water is dried, and the greater part 
of it rubbed together with from three to four parts of pure 
nitre ; the mixture is gradually deflagrated in a red hot 
crucible. The residue is treated as § 100, A, directs. 
Another part is boiled with aqua regia, the solution filtered 
and the filtrate tested for mercury. The rest is tested for 
ammonia, as § 122 directs. 

§ 130. 

IV. CONFIRMATORY EXPERIMENTS. 

When the various bases, acids, and electro -negative bodies, 
present in the substance under examination have been detected, 
it is in many cases advisable, in others obsolutely necessary, to 


CONFIRMATORY EXPERIMENTS. 


253 


verify our conclusions. In many cases this is easily accomplished, 
since certain substances have such characteristic reactions that 
their presence or absence may at once be determined, although 
many other substances are present at the same time. But many 
substances have not such characteristic reactions, in which cases 
we must satisfy ourselves by a strict and minute examination, and 
by varying our processes, determine whether the phenomena 
usually indicating the presence of a substance, do not proceed 
from extraneous causes 

Thus ammonia may be erroneously supposed to be present in 
a substance, whilst it is in fact derived from the atmosphere of the 
laboratory, &c. 

In the course of this work we have pointed out those reactions 
which may be sought as confirmatory proofs, and the precautions 
necessary to secure the purity of our reagents. 


CHAPTER II. 


EXPLANATORY NOTES AND ADDITIONS TO THE PRACTICAL 

COURSE. 

I. Remarks on the preliminary examination. 

§ 105 . 

The sensible qualities of bodies, as I before remarked, may 
often enable us at once to deduce certain general conclusions, as 
to their nature, at least negatively. Thus, a white powder cannot 
be cinnabar, a light fiocculent body cannot be a compound of lead, 
&c. But the student must beware of forming . opinions prema- 
turely, respecting the nature of a body from its sensible properties 
only, lest it give rise to such preconceptions as may lead 
him to draw fallacious conclusions from the reactions which 
manifest themselves afterwards in the courso of the real exami- 
nation. 

In the examination of bodies, at a high temperature, small glass 
tubes may be often advantageously substituted for a metallic spoon, 
since they enable us to observe any substance which may volatilize 
in the process ; but as a new tube is needed in every experiment, 
the metallic spoons may serve in ordinary practice. 

With respect to the blow-pipe examination, the student must 
avoid drawing positive conclusions until he has acquired a certain 
degree of experience, from practice ; a slight incrustation may not 
imply the presence of a metal, nor his inability to effect a reduc- 
tion or to produce a colour by solution of cobalt, the absence of a 
substance sought. The blow-pipe phenomena are, indeed, in most 
cases unerring, but they are easily modified by adventitious cir- 
cumstances. 


ADDITIONAL REMARKS. 


255 


The preliminary examination is in no case to be passed over by 
the student. 

II. Additional remarks upon solution, &c. 

§ 100 . 

There is some difficulty in determining the limits of the two 
classes of bodies, soluble and insoluble, since these terms are but 
relative, and we use the phrases easily, and sparingly, or difficultly 
soluble ; and, indeed, these two classes merge into each other. 
Sulphate of lime which is soluble in four hundred and sixty-one 
parts of water might perhaps serve as a limit between these two 
classes, since it may still be distinctly detected in aqueous solu- 
tions by means of the very susceptible reagents which we possess 
for lime and sulphuric acid. 

When examining an aqueous fluid by evaporating a few drops of 
it upon a platinum plate, there remains sometimes a very minute 
residue, which lejives us in doubt as to the nature of the sub- 
stance ; in this case the fluid must, 1st, be tested with litmus 
papers ; 2nd, one drop of solution of chloride of barium added to a 
portion of it ; and, lastly, some carbonate of potash added to ano- 
ther portion. If these tests produce no alteration, it is unneces- 
sary to examine it further for acids or bases. We may in such 
cases feel certain, that the substance of which the residue remain- 
ing upon evaporation consists, will be better detected amongst the 
bodies insoluble in water, since both the acids and bases, which 
principally form sparingly soluble compoimds, are sensibly indi- 
cated by the above-mentioned tests. 

If water has dissolved any portion of the substance under exa- 
mination, the student will always do well to examine separately 
this solution for acids and bases, as this will permit him to detect 
the nature of the compound under examination with greater faci- 
lity, and, moreover, will render his conclusions die safer, which 
advantages will counterbalance the disadvantage of meeting some- 
times with the same substance in the aqueous and in the acid 
solution. 


250 


ADDITIONAL REMARKS. 


The following substances are insoluble in water, but soluble in 
hydrochloric acid or in nitric acid, (with some exceptions,) the 
phosphates, arseniates, arsenites, borates, carbonates, and oxalates 
of the earths and metals ; and also several tartrates, citrates, 
malates, benzoates, and succinates, the oxides and sulphurets of 
the heavy metals, alumina, magnesia, many metallic iodides and 
cyanides, &c. Nearly all of these compounds are decomposed, if 
not by dilute, yet by boiling concentrated hydrochloric acid, (for 
the exceptions vide § 127,) but this decomposition gives rise to 
tho formation of insoluble compounds when oxide of silver is pre- 
sent, and of sparingly soluble compounds in the presence of prot- 
oxide of mercury and lead. This is not the case with nitric acid, 
and thus we often effect a complete solution by its means in cases 
where hydrochloric acid has left a residue. But nitric acid, be- 
sides the substances insoluble in simple acids, leaves also oxide of 
antimony, peroxide of tin, peroxide of lead, &c. undissolved, 
whilst it dissolves many other substances more or less completely- 
When, therefore, the compound under examination is not com- 
pletely dissolved by nitric acid, (with the exception of sulphur, 
which may have separated,) we must in the course of analysis 
again have recourse to the hydrochloric solution, in order to assign 
exact limits in some measure to the third class of substances _ 
viz. those bodies which are insoluble in water and simple acids. 

With regard to the solution of pure metals or alloys, we must 
remark, that white precipitates frequently arc formed upon boiling 
with nitric acid, though no tin or antimony be present. Inexpe- 
rienced students often confound these precipitates with the oxides 
of these two metals, although their external appearance is quite 
different. These precipitates consist of nitrates sparingly soluble 
in tho nitric acid present, but of easy solution in water. Oonse- 
quently, before we can pronounce these precipitates to consist of 
tin or antimony, wo must previously ascertain whether they are 
soluble in water. 


DETECTION OF THE BASES. 


257 


III. Additional remarks upon the real examination 
From § 107 to § 129. 

A. General survey and explanation of the analytical 

course. 

a. detection of the bases. 

Wo have divided the bases into six groups, (vide Chapter III. 
Part I.) and explained the method of detecting and isolating the 
individual bases. These objects we have kept in view in the prac- 
tical course, and as a correct apprehension of this is of primary 
importance, we subjoin a brief explanation of the grounds of our 
division, — a key, as it were, to the analytical course of study, so far 
as those bases are concerned. The general reagents which we em- 
ploy in the course of analysis to divide the bases into principal 
groups, are — hydrochloric acid, sulphuretted hydrogen, 
hydrosulpiiuret of ammonia, and CARBONATE of AMMONIA ; 
this is also the order of succession in which they are employed. 
Hydrosulpiiuret of ammonia performs a double paid. 

Let us suppose we have in solution all the bases, arsenious acid, 
and phosphate of lime, (which latter may serve as a type for the 
salts of the alkaline earths, soluble in acids, and precipitated by 
ammonia, unaltered.) 

Chlorine forms insoluble compounds with silver and mercury 
alone ; chloride of lead is sparingly soluble in water. The inso- 
luble protochloride of mercury corresponds with the protoxide of 
mercury. If, therefore, we add to our solution. 

1. Hydrochloric acid, we remove from the solution the metallic 
oxides of the first section of the fifth group, viz. the oxide of 
silver and the protoxide of mercury. A portion of the lead 
also may perhaps precipitate as chloride of lead, should the solu- 
tion be concentrated, this is, however, immaterial, as a sufficient 


s 


258 


DETECTION OF THE BASES. 


quantity of the lead remains in solution as to admit of its 
detection afterwards. 

Sulphuretted hydrogen precipitates the oxides of the fifth and 
sixth group completely from solutions containing a free mineral 
acid, as both the affinity which the metallic radicals of these oxides 
have for sulphur, and that which hydrogen possesses for oxygen, 
are so powerful as to overcome the affinity between the metal and 
oxygen, together with that between the oxide and a strong acid, 
EVEN THOUGH THE ACID BE PRESENT IN EXCESS. But none of the 
other bases are precipitated under those circumstances, the bases 
of the first, second, and third group forming no sulphur com- 
pounds insoluble in water; those of the fourth group are not pre- 
cipitated, because the affinity which their metallic radicals possess 
for sulphur, together with that manifested by hydrogen for oxygen, 
are not sufficiently powerful to overcome that of the metal for 
oxygen and of the oxide for a strong acid, if the latter is not 

PRESENT IN EXCESS. 

If, therefore, after the removal of oxide of silver and of prot- 
oxide of mercury, by means of hydrochloric acid, wo add to our 
solution, (which still contains free hydrochloric acid.) 

2. Sulphuretted hydrogen : we remove from it the rest of the 
oxides of the fifth, together with those of the sixth group, viz. 
OXIDE OF LEAD, PEROXIDE OF MERCURY, OXIDE OF COPPER, OXIDE 
OF BISMUTH, OXIDE OF CADMIUM, PEROXIDE OF GOLD, PEROXIDE 
OF PLATINUM, PROTOXIDE OF TIN, PEROXIDE OF TIN, OXIDE OF 
ANTIMONY, ARSENIOUS ACID, and ARSENIC ACID. All the Other 
oxides remain in solution, either unaltered or reduced to a lower 
degree of oxidation, e. g. peroxide of iron, chromic acid, &c. 

The sulpliurets corresponding with the oxides of the sixth 
group have the property of combining with electro-positive metallic 
sulpliurets (the sulpliurets of the alkali metals) forming sulphur 
salts soluble in water, whilst the sulpliurets corresponding with 
the oxides of the fifth group do not possess this property. If, 
therefore, we treat all the sulpliurets precipitated by sulphuretted 
hydrogen from acid solution, with 


DETECTION OF THE BASES. 


250 














•3. Hydrosulphuret of ammonia, or sulphuret of potassium, 
the bisulphurets of mercury, lead, copper, bismuth, and cad- 
mium will remain undissolved, whilst the other bisulphurets 
are dissolved as the double sulphdrets of gold, platinum, 
antimony, tin, ARSENIC, and ammonium or potassium, and 
from this solution they are precipitated upon the addition of an 
acid, either unaltered, or having acquired a higher degree of sul- 
plmration, by receiving sulphur from the hydrosulphuret of am- 
monia, (sulphuret of tin.) In this process the acid decomposes 
the sulphur salt formed. The sulphur base (hydrosulphuret of 
ammonia or sulphuret of potassium) is decomposed, at the ex- 
pense of the constituents of decomposed water, into an oxygen 
base (ammonia or potash) and sulphuretted hydrogen ; the 
former combines with the acid added, the latter escapes, and 
the liberated electronegative sulphuret precipitates. (If the acid 
is an hydracid, its radical combines with the ammonium and its 
hydrogen with the sulphur.) Sulphur precipitates at the same 
time, the hydrosulphuret of ammonia always containing sulphur in 
excess. This sulphur renders the colour of the precipitated sul- 
phurets lighter, which must be always borne in mind, when deter- 
mining their nature. 

Of the oxides still in solution, the alkalies, the alkaline earths, 
alumina and oxide of chromium have remained so, because their 
sulphur compounds are soluble in water, or because their salts are 
not at all affected by sulphuretted hydrogen ; the oxides of the 
fourth group would have been precipitated by sulphuretted 
hydrogen, had not the free acid present prevented their precipita- 
tion, as their corresponding sulphur compounds are insoluble in 
water. If, therefore, this free acid be removed, i. e. if the solution 
be made alkaline and sulphuretted hydrogen added, or if, what 
answers both purposes at once, 

4. Hydrosulphuret of ammonia bo added to the solution, the 
sulphurets corresponding with the oxides of the fourth group are 
precipitated, viz. : sulphuret of iron, sulphuret of man- 
ganese, SULPHURET OF COBALT, SULPHURET OF NICKEL, and 

S 2 


200 


DETECTION OF THE BASES. 


8ULPHURET OF ZINC, and at till) Sftmc time ALUMINA, OXIDE OF 
chromium, and phosphate of LIME, are precipitated, the affinity 
which the ammonia possesses for the acid of the salt of 
oxide of chromium or of alumina, or for the acid which keeps 
the phosphate of lime in solution, causing decomposition of the 
water and subsequently formation of oxide of ammonium and of 
sulphuretted hydrogen. The former combines with the acid, the 
latter escapes, incapable of entering into combination with the 
oxides deprived of their acids, or with the phosphate of lime, — the 
oxides and the limesalt precipitate. We have now remaining in 
solution only the alkaline earths and the alkalies. The neutral 
carbonates of the former are insoluble in water, whilst those of the 
latter are soluble. If, therefore, we add 

5. Carbonate of ammonia and apply heat, in order to decom- 
pose acid carbonates which may peradventure have been formed, 
all the alkaline earths ought to precipitate. This is, however, the 
case only as regards barytes, strontian, and lime ; of magnesia 
we know that, owing to its disposition of forming double com- 
pounds with ammoniacal salts, it precipitates only in part, or, not 
at all, in presence of another ammoniacal salt. To avoid this 
uncertainty, sal ammoniac is added previous to the addition of 
carbonate of ammonia, in order completely to prevent the preci- 
pitation of magnesia. 

We have now still in solution, magnesia and the alkalies; of 
the presence of magnesia we may assure ourselves by means of 
phosphate of soda and ammonia ; but for its separation we 
pursue a different way, since the presence of phosphoric acid 
would impede the further progress of the analysis. The process 
which we employ is based either upon magnesia being insoluble 
in its pure state or as a carbonate. The substance under exami- 
nation is heated to redness in order to expel the ammoniacal salts, 
and the magnesia is then either precipitated by means of baryte s 
whilst the alkalies remain in solution ; or the substance is heated 
to redness, with the addition of sulphuric acid, and the sulphates 
formed are by decomposition with acetate of barytes, converted 


DETECTION OF THE ACIDS. 


201 


into acetates, and these, by the application of a red heat, into car- 
bonates ; upon treating these latter with water, carbonate of mag- 
nesia remains, wliilst the alkaline carbonates are dissolved. A 
fresh specimen must, of course, be employed for the detection of 
ammonia. 


b. DETECTION OF THE ACIDS. 

Previous to entering upon the examination for acids and elec- 
tro-negative substances, we must first consider which of these 
bodies may and which of them cannot be present according to the 
detected bases, and accordingly to the solubility of the substances 
under examination ; thus we shall avoid making unnecessary ex- 
periments. A table useful for this purpose, will be found in the 
appendix. The general reagents employed for the detection of 
acids are, for the inorganic acids, chloride of barium and 
nitrate of silver ; for the organic acids, chloride of cal- 
cium and perciiloride of iron. It is therefore indispensable, 
first to assure ourselves whether we have to operate upon a sub- 
stance containing inorganic acids alone, or organic acids alone, or 
both together. When examining for bases, the general reagents 
serve for the real separation of the various groups of bases from 
each other ; in the examination for acids, we only use them to 
assure ourselves of the presence or absence of the ueids belonging 
to the different groups. 

Let us suppose we have in an aqueous solution all the acids we have 
treated of in the present work, combined, for instance, with soda. 

Barytes forms insoluble compounds with sulphuric acid, phos- 
phoric acid, arsenious acid, arsenic acid, carbonic acid, silicic 
acid, boracic acid, chromic acid, oxalic acid, tartaric acid, and 
citric acid; these compounds are soluble in hydrochloric acid, 
with the exception of sulphate of barytes. If therefore to a 
portion of our neutral or neutralized solution, we add 

1 . Chloride of barium , the presence of at least one of these 
acids will immediately become manifest. Upon treating the pre- 
cipitate formed with hydrochloric acid, the presence of sulphuric 
acid will be detected, as all the salts of barytes are soluble in this 


202 


DETECTION OF THE ACIDS. 


menstruum, with the exception of the sulphate. When sulphate of 
barytes is present, the reaction with chloride of barium does not 
enable us to detect all the other acids enumerated with safety. 
For upon filtering the hydrochloric solution of the precipitates 
and supersaturating with ammonia, the borate, tartrate, citrate, 
&c. of barytes do not precipitate again, being kept in solution by 
tho sal ammoniac formed. Chloride of barium, therefore, cannot 
be employed to separate tho individual acids from each other, and 
thus is of no use for their individual detection, except for that of 
sulphuric acid. It is, however, of great importance as a reagent, 
since the non-formation of a precipitate in neutral or alkaline solu- 
tions, upon its application, proves at once tho absence of a consi- 
derable number of acids. 

Silver forms compounds insoluble in water, with chlorine, 
iodine, bromine, and cyanogen ; and oxide of silver, with phos- 
phoric acid, arsenious acid, arsenic acid, boracic acid, chromic 
acid, silicic acid, oxalic acid, tartaric acid, and citric acid. All 
these compounds are soluble in ammonia, with the exception of 
iodide of silver, and in nitric acid, with the exception of iodide, 
chloride, bromide, and cyanide of silver. If, therefore, we add to 
our solution (which must be completely neutral) 

2. Nitrate of silver, we detect immediately the presence of one 
or several of the acids enumerated; chromic acid, arsenic acid, and 
several other acids, the silver salts of which are coloured, may 
even be individually detected with a certain degree of safety, by 
the colour of their precipitates. If we add nitric acid to the pre- 
cipitate, we detect the presence of the haloid compounds, as these 
remain undissolved, whilst the oxido salts are dissolved. The 
complete separation and individual detection of those acids which 
form insoluble compounds with oxides of silver, are prevented by 
the same cause which renders the individual detection of acids by 
chloride of barium unsafe. For the ammoniacal salt formed pre- 
vents the reprecipitation by ammonia, of several salts of silver, 
from the acid solution, nitrate of silver serves us therefore, besides 
detecting chlorine, iodine, bromine, and cyanagon, and indicating 
chromic acid, &c., especially to prove at once tho absence of many 


DETECTION OF THE ACIDS. 


2(33 


acids, if it produces no precipitate in neutral solutions. The 
behaviour of solutions under examination with chloride of barium 
and with nitrate of silver, therefore, points out at once what course 
we have further to pursue in our investigation. Thus, for instance, 
if chloride of barium has produced a precipitate, whilst we have 
obtained none by nitrate of silver, it is not necessary to test for 
phosphoric acid, chromic acid, boracic acid, silicic acid, arsenious 
acid, arsenic acid, oxalic acid, tartaric acid, and citric acid, pro- 
vided always that the solution does not already contain ammo- 
niacal salts. The same is the case if we obtain a precipitate by 
nitrate of silver, but none by chloride of barium. Returning to 
our first supposition, viz., that all acids are present in the com- 
pound under examination, we have thus detected chlorine, 
BROMINE, iodine, and cyanogen, (for their separation and indi- 
vidual detection, vide § 100,) as well as sulphuric acid, and we 
have reason further to test for all the other acids precipitated by 
those two reagents. Their detection is based upon the results of 
special experiments, which have already been explained in the 
course of the present work : the same applies to the other inor- 
ganic acids, and thus also to nitric acid and chloric acid. 

Of the organic acids, oxalic acid, tartaric acid, and paratartaric 
acid, are precipitated by chloride of calcium, from aqueous solu- 
tions, at a low temperature, even in the presence of sal ammoniac ; 
but the precipitation of citrate of lime is prevented by the presence 
of ammoniacal salts, and takes place only upon boiling or upon 
mixing the solution with alcohol ; the latter means is also em- 
ployed for the separation of oxalate of lime from aqueous solu- 
tions. If, therefore, we add to our solution, 

3. Chloride of calcium and sal ammoniac, oxalic acid, 
tartaric acid, and paratartaric acid are precipitated, but 
the lime-salts of several inorganic acids, which have not yet been 
separated, precipitate at the same time (phosphate of lime, for 
instance). We must therefore select, for the individual detection 
of the precipitated organic acids, such reactions only as do not 
admit the possibility of confounding the organic acids with the 
inorganic acids precipitated at the same time. For the detection 


264 


SPECIAL REMARKS. 


of oxalic acid wo thus select solution of gypsum, with the addition 
of acetic acid (§ 98, c, 4), for the detection of tartaric anti para- 
tartaric acid; we treat the precipitate produced by chloride of 
calcium, with solution of potash, since the lime-salts of these two 
acids alone dissolve in this menstruum, at a low temperature, whilst 
all the other insoluble lime-salts remain undissolved. 

Of the organic acids we have now still in solution citric acid 
and malic acid, succinic acid and benzoic acid, acetic acid and 
formic acid. Citric acid and malic acid precipitate upon alcohol 
being added to the fluid filtered off from the oxalate, tartrate, &c., 
of lime, and which contains still chloride of calcium in excess. 
Sulphate and borate of lime always precipitate together with the 
malate and citrate of limo, if sulphuric acid and boracic acid are 
present ; we must therefore carefully guard against confounding 
the lime precipitates of these acids with those of citric acid and 
malic acid. The alcohol is then removed by evaporation, and 

4. Perchloride of iron added; this precipitates succinic acid 
and renzoic acid in combination w r ith peroxide of iron, whilst 
formic acid and acetic acid remain in solution. The methods 
for the further separation of the groups and the reactions where- 
upon the detection of the individual acids depends, have already 
been described. 


B. Special and additional remarks upon the systematic 

course of analysis. 

§ 114. 

We have at the beginning of § 1 14, given the instruction to 
mix neutral or acid aqueous solutions with hydrochloric acid- 
This acid must he added drop by drop. If no precipitate is 
formed, a few drops are sufficient ; if a precipitate is formed, the 
acid must be added until the precipitate ceases to increase and 
the fluid has acquired a distinct acid reaction. The addition of 
large proportion of hydrochloric acid is not only unnecessary, but 


ADDITIONAL REMARKS. 


265 


injurious. The precipitate produced by hydrochloric acid in 
neutral or acid solutions may consist of chloride of silver, proto- 
chloride of mercury, chloride of lead, and a basic salt of antimony. 
The two latter substances redissolve upon diluting and heating the 
acid fluid, and thus the non-solution of the precipitate upon the 
application of these processes, is an indication of the probable 
presence of chloride of silver or protochloride of mercury. Should 
compounds of antimony or bismuth be present, this dilution with 
water will separate from them insoluble basic salts in a state of most 
minute division ; these must be redissolved by the addition of hydro- 
chloric acid, before we can draw any correct conclusion from the re- 
maining or disappearing of the precipita te produced by hydrochloric 

i acid. If we have to operate upon an alkaline solution, the hydro- 
chloric acid must be added, until the fluid manifests a strong acid 
reaction. A great excess of the acid must, however, be avoided. 
The substance which causes the alkaline reaction of the fluid, is 
neutralized by the hydrochloric acid, and the bodies combined 
with it, or dissolved in it, separate. If the alkali present was in 
a free state, oxide of zinc, for instance, alumina, &c., may be pre- 
cipitated. But these redissolve in an excess of the hydrochloric 
acid, whilst chloride of silver, if present, will not redissolve, and 
chloride of lead only sparingly. If a metallic sulphur salt be the 
cause of the alkaline reaction, the electro-negative sulphuret (e. g. 
sulphuret of antimony) will precipitate, on the addition of the 
hydrochloric acid ; whilst the electro-positive sulphuret (e. g. sul- 
phuret of sodium) will form chloride of sodium and sulphuretted 
hydrogen, with the constituents of hydrochloric acid. If an alka- 
line carbonate, or an alkaline sulphuret, be the cause of the alka- 
line reaction, carbonic acid or sulphuretted hydrogen will eseapo. 
All these phenomena ought to be carefully observed, for they not 
merely point out the presence of the relative substance, but also 
exclude entire' series of substances from the further examination. 

§ 115 . 

We have already had occasion to remark, that upon adding a 
reagent (e. g. sulphuretted hydrogen) to a fluid under examina- 


I 


200 


ADDITIONAL REMARKS. 


tion x a precipitate may or may not ensue. If a precipitate is 
formed, this may be, a, white, b, yellow, c, orange, tl, brown or 
black. Every one of these various cases is a different answer 
given to the question put by means of the reagent, and every 
answer has a different meaning. An accurate distinction of the 
individual case is, therefore, indispensable. Any error here must 
prevent the student from obtaining correct results. 

The colour of the precipitate is almost invariably pointed out 
as a criterion in the systematic course of analysis. We may pre- 
sume that a darker precipitate will sometimes conceal one of a 
lighter colour, and thus, e. g. that yellow sulpliuret of arsenic 
may be present, invisible in a precipitato of black sulpliuret of 
mercury ; and so we may also conclude that no dark precipitate 
can be contained in a light-coloured one, e. g. no black precipi- 
tate in a white. These conclusions cannot, however, always be 
drawn with the same degree of safety, all colours not contrasting 
so pointedly with each other as black and white ; but many of 
them rather merging into each other, e. g. yellow and orange. 
Whenever the colour of the precipitate admits of any doubt as 
to its nature, it is always advisable to pursue that course which 
the darker of the colours in question indicates, since in this re- 
gal’d has been had to all the metals which can possibly have pre- 
cipitated, whilst in the other the metallic precipitates of darker 
colour are disregarded. The safer way is always to bo preferred, 
although it may be the more protracted. 

A judicious distribution and economy of time is especially to 
be studied in the practice of analysis ; many of the operations 
may be carried on simultaneously, which the student will readily 
perceive and arrange for himself. 

In such cases, where we have before us only metallic oxides of 
the sixth group, (e. g. oxide of antimony,) and oxides of the 
fourth group, (e. g. the oxides of iron,) it is not necessary for 
their separation to precipitate them from acidified solutions by 
means of sulphuretted hydrogen, but we may at once add hydro- 
sulphurct of ammonia in excess to the neutralized solution. The 
sulpliuret of iron, &c., will then be obtained in a precipitate, 


ADDITIONAL REMARKS. 


207 


whilst the antimony, &c., will remain in solution, from which, 
upon the addition of an acid, it will immediately precipitate a 
sulpliuret of antimony. This method has the advantage of ren- 
dering the Huid less dilute than when sulphuretted hydrogen is 
employed, and moreover of facilitating and accelerating the 
operation. 


§ 110 . 

When digesting the precipitates produced by sulphuretted 
hydrogen from acid solutions, with hydrosulpliuret of ammonia, 
it is indispensable to apply this latter reagent in a correct propor- 
tion. A small quantity is generally sufficient, but if sulpliuret of 
tin be present, a somewhat larger amount must be employed. In- 
experienced students, however, use so much of it, that, upon the 
addition of an acid, sulphur precipitates to such an amount 
that the colour of the metallic sulpliuret, which precipi- 
tates at the same time, is quite obscured and concealed by it. 
The separation and individual detection of oxide of antimony, 
peroxide of tin, and arsenic, is not very easy if all three oxides 
have been precipitated as sulpliurets. Inexperienced students 
will find it difficult safely to detect and separate them before 
the blow-pipe. Of the many methods applicable for the dis- 
tinction of these three metals, that given at § 110 has been 
proved the safest by experience. If sulpliuret of arsenic, sul- 
phuret of untimony, and sulpliuret of tin, are deflagrated with 
nitre in excess, and enrbonate of soda, the metals and the sul- 
phur oxidize at the expense of the oxygen of the nitric acid : we 
have, therefore, in the fused mass alkaline arseniate, antimoniate, 
sulphate, and stannate, besides excess of nitre and carbonate of 
soda. On treating with water, the alkaline sulphate and arse- 
niatc are dissolved ; the alknline antimoniato is decomposed ; an 
insoluble acid salt remains, whilst a small amount of antimonic 
acid is dissolved in the form of a basic salt. A portion of the 
peroxido of tin also dissolves in the carbonated alkali present. 
If boiling water is employed, the amount of the dissolved anti- 



268 


ADDITIONAL REMARKS. 


monic acid ancl peroxide of tin is not inconsiderable, whilst it is 
but minute in cold water ; tlio latter is therefore preferable to 
boiling water in this operation. If the alkaline solution obtained 
is then saturated with nitric acid, and heat applied, the dissolved 
peroxide of tin and antimonic acid precipitate ; but this precipi- 
tate is never free from arsenic. This will show how carefully we 
ought to avoid getting much peroxide of tin or antimonic acid in 
solution. In the fluid saturated with nitric acid, or slightly 
acidified, filtered off from the precipitate formed, we have now 
still arseniated and sulphated alkali. One portion of this fluid is 
tested, as stated § 116, with solution of silver and ammonia, an- 
other portion with solution of lead, Since the fluid must be per- 
fectly neutral to render the arseniatc of silver visible, and since 
it is not always easy to hit upon the exact neutralization point, 
the fluid, after the addition of the solution of silver, is covered 
with a layer of dilute ammonia. This is the easiest method of 
producing a precipitate when but small quantities of arsenic are 
present. On the precipitation with solution of acetate of lead, we 
obtain a mixture of sulphate and arseniate of oxide of lead. The 
presence of the sulphate of lead renders the quantity of the precipi- 
tate greater, and thus its collection and testing before the blow-pipe 
more easy ; it moreover increases the bulk of the button obtained. 
Though by means of these reactions the presence of arsenic may 
be proved beyond doubt, yet the production of metallic crusts is 
the safest test. 

If the residue remaining upon treating the deflagrated mass 
with water, and which is to be examined for tin and antimony, 
be not carefully washed, and thus freed from all the nitre still 
adhering to it, previous to fusing with cyanide of potassium, ex- 
plosions wfill take place, (§ 101, a, 3,) whereby not only the test- 
specimens are thrown off, but the operator himself may meet with 
some injury. 


§ 117. 

If the sulphurets of the second section of the fifth group arc 


ADDITIONAL REMARKS. 


2GA 


heated to the boiling point •with nitric acid, lead, bismuth, copper, 
and cadmium, oxidize at the expense of a portion of the nitric 
acid, which decomposes into nitric oxide and oxygen, the sulphur 
separates, and the oxides formed combine with another portion 
of the nitric acid, forming soluble nitrates. Sulphuret of mer- 
cury is not decomposed by nitric acid, provided no chloride be 
present at the same time, owing to imperfect rinsing. Ammonia 
decomposes all the metallic nitrate dissolved. But the oxides of 
lead and bismuth are insoluble in an excess of ammonia, whilst 
those of cadmium and copper are dissolved by this reagent. 
Ammonia therefore affords us a means of testing the solution for 
the presence of the oxides of lead and bismuth, as w r ell as of pre- 
cipitating and separating them from it. The presence of oxide 
of copper is also detected by this reagent; the ammonio -nitrate 
of copper, which is formed upon its addition to the fluid under 
examination, imparting a blue colour to the fluid. The causes 
whereupon the further separation and detection of the four metals 
in question depends, have already been sufficiently explained at 
§91, (recapitulation and remarks.) With regard to the de- 
tection of bismuth, it must be remarked, that it never succeeds if 
the excess of acid present is not as slight as possible ; this is best 
attained in the manner described § 117. But if the operator 
evaporates only nearly to dryness, so much acid frequently re- 
mains present, that the separation of a basic salt cannot be 
accomplished. 

Besides the method given at § 91, (recapitulation and remarks,) 
and at § 117, for the distinction of cadmium, copper, lead, and 
bismuth, the following method also leads with great safety to the 
desired end. Carbonate of potash is added to the nitric solution 
as long as any precipitation takes place ; solution of cyanide of 
potassium in excess is then added, and heat applied. Lead and 
bismuth are hereby completely separated as carbonates, whilst 
copper and cadmium are obtained in solution as the double 
cyanides of copper and potassium, and cadmium and potassium. 
Lead and bismuth may then easily be separated by means of 
sulphuric acid ; copper and cadmium, by adding to the solution 


270 


ADDITIONAL REMARKS. 


of their cyanides in cyanide of potassium, sulphuretted hydrogen 
in excess, and applying heat ; some more cyanide of potassium 
must then he added to redissolve the sulphuret of copper, which 
peradventure may also have pi*ecipitated. A yellow precipitate 
of sulphuret of cadmium, insoluble in cyanide of potassium, indi- 
cates cadmium. The fluid is filtered off, and hydrochloric acid 
added to the filtrate ; the formation of a black precipitate of sul- 
phuret of copper indicates copper. The presence of mercury is 
indeed already proved by a black residue remaining, upon heating 
the sulphurets with nitric acid. A more minute examination of 
any residue remaining upon boiling with nitric acid, is, however, 
necessary, always provided this residue be not pure yellow sul- 
phur, which in most cases floats on the surface of the fluid. The 
reasons for this further examination are the following : separated 
sulphur frequently envelopes small particles of the other black 
sulphurets, and for this reason appears black here and there. 
Sulphuret of mercury, moreover, may, under certain circum- 
stances, lose its black colour, and the precipitate in that case be 
confounded with sulphate of lead, (into which substance a portion 
of the sulphuret of lead pi-esent is in most cases converted,) or 
with peroxide of tin, (which may have been formed by the action 
of nitric acid upon sulphuret of tin present, and not completely 
removed by hydrosulpliuret of ammonia) . The test with polished 
copper is the most convenient, and yields the quickest result It 
must, however, be remarked that errors occur more frequently, 
■when employing this test, than when we select the reaction with 
protochloride of tin. When employing the latter reagent, we 
must especially assure ourselves of its being still undecomposed, 
and of the solution of mercury containing no nitric acid. If after 
the method described, the protoxide of mercury has first been se- 
parated by hydrochloric acid, and a precipitate of sulphuret of 
mercury is formed, upon the addition of sulphuretted hjdiogen, 
this corresponds always with the peroxide and perchloride, &c. of 
mercury. If wo have to operate upon an aqueous solution, or a 
solution in very dilute hydrochloric acid, it existed as such in the 
original substance. But when we have a nitric solution befoie us, 


ADDITIONAL REMARKS. 


271 


it may lmvo originally existed as protoxide, and subsequently ac- 
quired a higher degree of oxidation. 


§ 118. 

The precipitate produced by hydrosulphuret of ammonia, may 
(as we have already stated, page 259) consist of sulphurets, of 
oxides, and of the phosphates of the alkaline earths, phosphate of 
alumina, oxalate of lime (barytes and strontian.) The borates of 
the alkaline earths and the oxalate of magnesia would, moreover, 
be precipitated, but they remain in solution owing to the sal am- 
moniac formed in the fluid or added to it. Upon dissolving the 
precipitate in hydrochloric acid, or in aqua regia, the metallic sul- 
phurets and the hydrated oxides are converted into soluble chlo- 
rides, whilst the phosphates and oxalates dissolve without decom- 
position. If to this acid solution, ammonia is added, the phos- 
phates and oxalates are re-precipitated, and, together with them, 
alumina, oxide of chromium, and peroxide of iron fall down, as 
these do not (like the oxides of manganese, nickel, cobalt, and 
zinc) form soluble double compounds with ammoniacal salts. 
This precipitation by ammonia, in presence of sal ammoniac, is 
the base whereon the further distinction and individual detection 
of the substances enumerated depends. At this result we may also 
arrive by merely adding sal ammoniac and ammonia in excess to 
the fluid filtered from the precipitate produced by sulphuretted 
hydrogen, after havingexpelled the excess of sulphuretted hydrogen 
by boiling, and converted the iron which peradventure maybe pre- 
sent, into peroxide of iron, by heating with nitric acid. We ob- 
tain thus, of course, the peroxide of iron, the alumina, oxide of 
chromium, and the phosphates, &c., of the alkaline earths alone in 
the precipitate, whilst the manganese, cobalt, nickel, and zinc, are 
contained in the fluid which runs off, and may then be precipi- 
tated by means of hydrosulphuret of ammonia. Under certain 
circumstances this method is preferable to the first, and may then 
be employed with advantage ; but in general it requires more time 
than the other. With regard to the further detection of nickel, 

6 


272 


ADDITIONAL REMARKS. 


cobalt, manganese, and zinc, wo have nothing to add to § 118, 2 , 
except that ammoniacal salts must not he present, if the separa- 
tion of these four metals from each other is to succeed after the 
method described at § 118, 2. But as the separation of manga- 
nese, nickel, &c., from iron, &c., depends upon the presence of 
ammoniacal salts, these must he removed, either by evaporating 
the solution and heating the residue to redness, or by precipitating 
these four metals again by hydrosulphuret of ammonia, (which 
latter method generally is preferable to the former.) The preci- 
pitato of the metallic sulphurets must, of course, be carefully 
washed. The separation of the peroxide of iron, and of the phos- 
phates and oxalates of the alkaline earths from alumina and oxide 
of chromium rests upon the solubility of the latter and the insolu- 
bility of the former compounds, in caustic potash ; and that of 
peroxide of iron from the salts of the alkaline earths, upon the 
circumstance that the precipitation of the former is prevented by 
adding tartaric acid to the acid solution, previous to the addition 
of ammonia, which is not the case with the latter. (Vide recap, 
and rcm. to § 88.) 


§ 127. 

% 

The third class of substances also has no strictly definable 
limits, as the solubility or insolubility of several compounds be- 
longing to it, depends very much upon the quantity and concen- 
tration of the acid and the time of boiling. Besides the difficultly 
soluble substances enumerated, we must especially look for many 
metallic sulphurets and iodides, which also only dissolve after 
some time in concentrated hydrochloric acid, at a high tempe- 
rature. If a substance is dissolved in nitric acid after long boiling, 
we must not conclude that protochloride of mercury is absent, 
since this substance, as we have already stated, is converted in 
this process into pemitrate of mercury and perchloride of mercury, 
and is thus dissolved. 

Chloride of silver, protochloride of mercury, and chloride of lead 


ADDITIONAL REMARKS. 


273 




nifty have been present in the original compound as such, or may 
Imve been formed upon treating with hydrochloric acid. The 
presence of chloride of lend has in that case already been detected 
in the aqueous solution ; of the original presence of the two other 
substances we may assure ourselves in the following manner. The 
substance insoluble in water is treated with dilute nitric acid. 
All the salts of protoxide of mercury and oxide of silver present 
are thereby dissolved, whilst the chlorides enumerated above re- 
main undissolved together with iodide of silver ; they are sepa- 
rated by means of ammonia, which at the same time allows us to 
detect the protoehloride of mercury. 

The decomposition of the sulphates of the alkaline earths may 
be effected also in the humid way by boiling them for some time 
with solution of carbonate of potash. But the fusion with the 
carbonate of potash and soda, yields far safer results, and leads 
quickly to the desired end, when operating upon small quantities. 
This method has moreover the advantage of leading to the safe 
detection of the presence of silicic acid. 

The sulphates of the alkaline earths are decomposed by the 
alkaline carbonates in such a manner as to give rise to the for- 
mation of carbonates of the alkaline earths and of sulphates of the 
alkalies. If the precipitate of the former be not carefully washed, 
previously to its solution in hydrochloric acid, sulphates of the 
alkaline earths will again be formed by the action of the sulpliated 
alkali still adhering to the precipitate ; this would render the ex- 
periment very unsafe at the least, since, for instance, all the bary- 
tes dissolved might precipitate again. 

Carbon has been connected with this third class, since it occurs 
sometimes in the course of examinations, and thus may become a 
great obstacle to the progress of the inexperienced student, if not 
prepared for its presence. Graphites is distinguished from the 
other forms of carbon by its difficult combustion before the blow- 
pipe, and its non-combustion in a platinum spoon ; besides the 
iron, which it generally contains in admixture, indicates its 
presence. 


274 


ADDITIONAL REMARKS. 


§ 128. 

The analysis of cyanogen compounds is not very easy in certain 
cases, and somotimes it is indeed extremely difficult to ascertain 
whether we have a cyanide before us or not. If, however, the 
phenomena which the substance under examination manifests, 
when heated to redness, (§ 105, A, I., 2,/ 1 ,) be carefully observed, 
and also whether upon boiling with hydrochloric acid any odour 
of hydrocyanic acid manifests itself, (§ 10G, A, 2,) the presence or 
absence of a cyanide will generally not long be doubtful. 

It must above all be home in mind that the insoluble cya- 
nogen compounds occurring in pharmacy, &c., belong to two quite 
different classes. They are either simple cyanides, or com- 
pounds of metals with ferrocyanogen, or with some other similar 
compound radical. 

All the simple cyanides are decomposed by boiling with 
concentrated hydrochloric acid, into metallic chlorides and 
hydrocyanic acid. Their analysis, therefore, is never diffi- 
cult. The ferrocyanides, &c., however, (to which the method 
given § 128 indeed exclusively refers,) undergo by acids such 
complicated decompositions that their analysis in this manner 
does not easily succeed. Their decomposition by alkalies is far more 
simple ; these precipitate the metal combined with the ferrocya- 
nide, &c., as oxide, by yielding their oxygen to it, and combining 
in their metallic state with the compound radicals, forming soluble 
ferrocyanide of potassium, &c. The method given at § 128 en- 
deavours first to effect a decomposition of this kind by means of 
carbonate of potash. If this succeeds, we have the advantage 
of obtaining the oxides as a precipitate, which circumstance ren- 
ders their further analysis simple ; if it does not succeed, we must 
have recourse to caustic potash. But in an excess of caustic 
potash, several oxides are soluble, such as oxide of lead, oxide of 
zinc, &c. If, therefore, e. g. the double ferrocyanide of zinc and 
potassium, be boiled with caustic potash, it will completely dis- 
solve in that menstruum. Were we to add an acid to this solu- 

5 


ADDITIONAL REMARKS. 


^75 


tion, we should re-obtain our origiual precipitate of the double 
ferrocyanide of zinc and potassium, and our experiment thus 
would be of no avail. To prevent this, we transmit sulphuretted 
hydrogen through the solution. All the heavy metals dissolved 
as oxides in the potash solution are thereby converted into sul- 
pliurets. Those of them which are insoluble in potash, such as 
sulphuret of lead, sulphuret of zinc, &c., precipitate, whilst those 
soluble in alkaline sulpliurets, such as sulphuret of tin, sulphuret 
of antimony, &c., remain in solution, and precipitate only upon 
the addition of an acid. 

The cyanogen is always contained in the liquid filtered from 
the precipitated oxides or sulphurets, as ferrocyanide, &c., of 
potassium, (provided always the compound before us has a double 
compound of cyanogen radicals). From most of them (ferro- 
cyanide, ferricyanide, chromicyanide, and manganocyanide of 
potassium) the cyanogen partly separates as hydrocyanic acid, 
upon boiling this solution with sulphuric acid, and may thus be 
easily detected. But the cobalticyanide of potassium is not de- 
composed by sulphuric acid, and this renders it difficult directly 
to prove the presence of cyanogen in this double compound. 
Upon fusion with nitre, all these double compounds are decom- 
posed, cobalticyanide of potassium not excepted. They must pre- 
vious to this operation be treated with an excess of - nitric acid, 
and then concentrated by evaporation, or else explosions will 
ensue. Caution in this operation is highy advisable. If we 
merely propose to detect the bases present in simple or double 
cyanides, it is in most cases sufficient either to heat the substance 
to redness for some time by itself, or better still, to fuse it 
together with the carbonates of potash and soda. By this pro- 
cess the metals are obtained either in their metallic state, or com- 
bined with carbon. If the compound has been fused together 
with the carbonated alkalies, we obtain in the dross, cyanide of 
potassium, if this substance has not been converted into cyanato 
of potash, owing to the adventitious presence of reducible oxides. 
(Vide § 100, d, 1.) 
























































APPENDIX TO PART SECOND. 


I- 


GENERAL SCHEME FOR A JUDICIOUS ARRANGEMENT OF THE 
SUCCESSION IN WHICH SUBSTANCES OUGHT TO BE ANALYSED. 


It is not a matter of indifference whether the student, in ana- 
lysing for the sake of practice, follow no rule or order whatever 
in the selection of substances to be examined, or whether, on the 
contrary', his investigations and experiments follow a definite 
system. Many ways may lead to the desired end, but one of 
them invariably will prove the shortest. I will therefore here 
point out a system which experience has shown will lead safely 
and rapidly to the object in view. 

Let the student take one hundred compounds, distributed 
according to the following scheme, and the successful examination 
of these will be amply sufficient to enable him to attain the desired 
degree of skill in practical analysis. When analysing for the sake 
of practice only, the student must above all things possess the 
means of verifying the results obtained by his experiments. The 
compounds to be examined ought, therefore, to be mixed by a 
friend who knows their exact composition. 


A. From 1 to 20. 

Aqueous solutions of simple salts : e. g. sulphate of soda, 
sulphate of lime, chloride of copper, &c ; — for the acquisition of 


278 


APPENDIX TO PART SECOND. 


the method to he pursued in the analysis of substances soluble in 
water, and which contain but one base. In these investigations 
it is only intended to ascertain which base is present in the fluid 
under examination, without regard to the detection of the acid ; 
it is not necessary to prove that no other base is present, besides 
the one detected. 


B. From 21 to 50. 

Salts, &c., (containing one base and one acid,) in a solid 
form, as powder : e. g. carbonate of barytes, borate of soda, 
phosphate of lime, arsenious acid, chloride of sodium, tartar, 
acetate of copper, sulphate of barytes, chloride of lead, &c. ; — 
to learn how to convert a solid substance to a state which 
admits of its examination, (solution, or fluxing,) how to detect 
one metallic oxide, even though the substance under examination 
be not soluble in water, and how to prove the presence of one 
acid. Base and acid must be detected ; it is not necessary to 
prove that no other constituents, &c., are present. 

C. From 51 to 70. 

Aqueous or acid solutions of several bases; — to acquire 
the method of separating and distinguishing several metallic 
oxides. It is necessary to prove that no other bases are present 
besides those detected. No regard is paid to the acids. 

I. From No. 51 to GO. To acquire the method of separating 
the metallic oxides into the principal groups. The solutions con- 
tain, therefore, e. g. potash, lime, and lead ; — copper, iron, and 
arsenic ; — barytes, antimony, bismuth, and potash, &c. 

II. From No. 61 to 70. To acquire the method of detect- 
ing side by side the individual bases belonging to the same group. 
The solutions contain, e. g. potash, soda, and ammonia ; zinc, 
manganese, and nickel ; — copper, mercury, and lead ; — antimony, 
tin, arsenic, &c. 


APPENDIX TO PART SECOND. 


279 


1). From 71 to 80. 

Aqueous solutions containing several acids, either in 
THEIR FREE OR IN THEIR COMBINED STATE, e. g. Sulphuric acid, 
phosphoric acid, and boracic acid ; — carbonic acid, sulphuretted 
hydrogen, and hydrocyanic acid; — tartaric acid, citric acid, and 
malic acid ; — chlorine, iodine, and bromine ; — nitric acid, hydro- 
chloric acid, and oxalic acid ; — to acquire the method of detecting 
several acids contained in the same compound. It is necessary 
to prove that no other acids are present besides those detected. 
The bases are disregarded. 


E. From 81 to 100. 

Alloys, minerals, and mixed substances of every de- 
scription ; — for further practice, and to prove that the student has 
attained the object ho had in view when entering upon these expe- 
rimental examinations. All the constituents of a substance under 
examination must be detected ; the nature of the substance must 
be examined. 


280 


II. 

TABLE 


OF THK 

MORE FREQUENTLY OCCURRING FORMS AND 
COMBINATIONS OF THE SUBSTANCES CONSIDERED IN 
THE PRESENT WORK, 

WITH ESPECIAL REGARD TO THE CLASSES, TO WHICH THEY BELONG 
ACCORDING TO THEIR VARIOUS DEGREES OF SOLUBILITY 

IN WATER, IN HYDROCHLORIC ACID, OR IN NITRIC ACID. 


PRELIMINARY REMARKS. 

The various classes to which compound substances belong 
according to the division specified at § JOG, are expressed by 
figures. Thus 1 or I means a substance soluble in water ; 2 or II 
a substance insoluble in water, but soluble in hydrochloric acid, or 
nitric acid ; 3 or III a substance insolublo both in water and 
acids. The Roman figures denote officinal and more frequently 
occurring compounds, whilst the Arabian figures indicato less 
frequently occurring compounds. For those substances standing 
as it were, on the limits between the various classes, the figures of 
the classes in question are jointly expressed : thus 1 — 2 signifies 
a substance difficultly soluble in water, but soluble in hydrochloric 
acid or nitric acid; 1 — 3 a body difficultly soluble in water and 
the solubility of which is not increased by the addition of acids ; 
and 2 — 3 a substance insoluble in water and difficultly soluble in 


PRELIMINARY REMARKS. 


281 


hydrochloric acid and in nitric acid ; wherever the relation of a 
substance to hydrochloric acid is different from that to nitric acid, 
this is stated in the notes. 

The haloid salts and sulphur compounds will be found in the 
columns of the protoxide and peroxide. Most of the salts given 
are neutral, the basic and acid and double salts are mentioned 
in the notes; the small figures placed near the corresponding 
neutral or simple salts, refer to these. Cyanogen, chloric 
acid, citric acid, malic acid, benzoic acid, succinic acid, and 
formic acid, are of more frequent occurrence only in combi- 
nation with a few bases, and have therefore not been admitted into 
the table. The most frequently occurring combinations of these 
substances are : cyanide of potassium I, ferrocyanide of potassium 
I, ferricyanide of potassium I, sesqui-ferrocyanide of potassium 
(Prussian blue) III, ferrocyanide of zinc and potassium II — 
III, chlorate of potass I, the nlkaline citrates I, the alkaline malates 
I, pcrmalate of iron I, the alkaline benzoates I, the alkaline succi- 
nates I, and the alkaline formiates I. 


282 


A TABLE OF THE VARIOUS FORMS 



KO 

NaO 

NH 4 O 

BaO 

SrO 

CaO 

MgO 

AI 2 O 3 

MnO 

FeO 

Fe203 

CoO 

NiO 

ZnO 


I 

I 

I 

I 

1 

I-TI 

II 

II 

I I 

II 

II 

II 

II 


s 

I 

I 

I 

I 

I 

I-1I 

2 


II 

II 

II 

15 

i« 

II 

Cl 

I 

I 

Il2 

I 

I 

I 

1 

1 

I 

I 

I 12 

1 

I 

1 

J 

I 

1 

1 

1 

1 

1 

1 


1 

1 

1 



1 

S03 

Ii 

I 

1 13 

III 

III 

I-III 

I 

1 1*13 

I 

I 

I 

1 

1 

I 

NOs 

I 

I 

1 

I 

I 

1 

1 

1 

I 

1 

1 

I 

I 

1 

PO 5 

1 

IlO 

IlO 

2 

2 

IIu 

2 

2 

2 

2 

II 

2 

2 

2 

C0 2 

12 

111 

I 

II 

II 

II 

II 


II 

2 


2 


II 

C* O 3 

I 3 

1 

I 

2 

2 

II 

2 

2 

2 

1-2 

1-2 

2 

2 

2 

BO,I 

14 

14 

1 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

A 

I 

I 

I 

I 

1 

1 

1 

1 


1 

1 

1 

1 

I 

T 

14-9 

17 

lc 

2 

2 

II 

1-2 

1 

1-2 

1-2 

la 

1 


2 

As Os 

I 

1 

1 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

3 

As O 3 

r 

1 

1 

2 

1 

2 




2 


2 

2 


Cr O 3 

1 

1 

1 

2 

2 

1 

1 

2 

1 


1 

2 

1 



NOTES 

1. SuLrHATE of potash and alumina I. 

2. Bicarbonate of potash I. 

3. Binoxalate of potash I. 

4. Tartarized borax I. 

5. Bitartrate of potash I. 

C. Tartrate of potash and ammonia I. 

7. Tartrate of potash and soda I. 

8. Tartrate of potash and peroxide of iron I. 

9. Tartrate of antimony and potash I. 

10. Phosphate of soda and ammonia I. 

1 1. Bicarbonate of soda I. 

12. Chloride of iron and ammonium I. 

13. Sulphate of ammonia and alumina I. 

14. Basic phosphate of lime II. 

15. Sulphuret of cohalt is easily decomposed by nitric acid, but 


/ 


283 


AND COMBINATIONS OF BODIES. 



CdO 

PbO 

SnO 

S 11 O 2 

BiO 

CuO 


2 

2l8 

2 

2&3 

2 

II 22 

s 

2 

2 

20 

20 

2 

23 

Cl 

1 

I-III 

I 

1 

I 

124 

J 

1 

II 

2 




S0.3 

I 

I 

1 

1 

1 

1 25 

NOs 

1 

I 



I 21 

I 

POs 

2 

2 




2 

C02 

2 

II 



2 

II 

C2 03 

2 

II 

2 


2 

2 

bo 3 

1-2 

2 

2 


2 

2 

A 

1 

Il9 

1 

1 

1 

I 26 

f 

1-2 

II 

1-2 


2 

1 

AsOs 


2 



2 

2 

As03 


2 




II 

CrO.i 


II-III 

2 


2 

2 


HG 2 0 

HgO 

AgO 

PtO-2 

AuO.i 

SbO.'i 

Cri On 

II 

II 

2 

2 


35 

II & III 

III 

III 


3 


11.36 


II-III 

1 28 

hi 

I? 2 -.r> 

I 34 

137 

I 

II 

II 

3 





1-2 

1 29 

i-iii 

1 


2 

I 

1-47 

I 

1 

1 



I 

2 

2 

2 




2 

2 

2 

2 





2 

2 

2 



1-2 

1 

1 


2 




2 

1-2 

1 

1 



1 

1 

1-2 

2 

2 



1 38 

1 

2 

2 

2 



2 

1 

2 

2 

2 



2 


2 

1-2 

2 



2 

2 


very difficultly by hydrochloric acid. This substance is not 
officinal. 

16. The same applies to sulphuret of nickel. 

17. The same applies to sulphuret of zinc. 

18. Minium is converted by hydrochloric acid into chloride of 

lead, by nitric acid into an oxide soluble in an excess of the 
acid, and into brown peroxide of lead, insoluble in nitric 
acid. 

19. Basic acetate of lead I. 

20. Sulphuret and bisulpliuret of tin are decomposed and dissolved 

by hydrochloric acid, whilst they are converted into inso- 
luble oxides by nitric acid in excess. Sublimed bisulpliuret 
of tin dissolves only in aqua regia. 

21. Basic nitrate of bismuth II. 

22. Ammoniacal oxide of copper I. 

23. Sulphuret of copper is difficultly decomposed by hydrochloric 

acid, but with facility by nitric acid. 


284 


NOTES. 


24. Chloride of copper and ammonium 1. 

2. r ). Sulphate of copper and ammonia 1. 

20. Basic acetate of copper, soluble partially in water, and com- 
pletely in acids. 

27. Basic protonitrate of mercury and ammonia II. 

28. Basic chloride of mercury and ammonium II. 

20. Basic persulphate of mercury II. 

80. Sulphuret of silver soluble only in nitric acid. 

81. Sulphuret of platinum is not affected by hydrochloric acid; 

boiling nitric acid converts it into a soluble sulphate of 
platinum. 

82. Chloride of platinum and potassium 1 — 3. 

83. Chloride of platinum and ammonium 1 — 3. 

34. Chloride of gold and sodium I. 

35. Oxide of antimony soluble in hydrochloric acid, hut not in 

nitric acid. 

36. Sulphuret of antimony and calcium 1 — 2. 

37. Basic chloride of antimony II. 

38. Tartrate of antimony and potash I. 


THE END. 


LONDON : 

PRINTED BY 0. J. PALMER, SAVOY STREET, STRAND.