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ELEMENTARY 
PHYSICS AND CHEMISTRY 



GREGORY AND SIMMONS 



FIRST STAGE 



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1905 

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ELEMENTARY PHYSICS AND 
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ELEMENTARY t^p,x 

PHYSICS AND chemistry';"/!,^ 



FIRST STAGE 



BY 

R. A. GREGORY 

PROFESSOR OF ASTRONOMY, QUEEN's COLLEGE, LONDON ; OXFORD 
UNIVERSITY EXTENSION LECTURER 

AND 

A. T. SIMMONS, B.Sc. (Lond.) 

ASSOCIATE OF THE ROYAL COLLEGE OF SCIENCE, LONDON 



'Ronton 
MACMILLAN AND CO., Limited 

NEW YORK : THE MACMILLAN COMPANY 

1906 

A/i rights reserved 



First Edition 1890. 

Reprinted 1900, 1902 (twice). 

Reprinted witli corrections, 1905, 1900, 



GLASGOW : PRINTED AT THE UNIVERSITY PRESS 
BY BOBERT MACLEHOSE AND CO. LTD, 



PREFACE. 

The course of elementary physics and chemistry commenced 
in this book is based upon a syllabus of work approved 
se\eral years aj^o by the Board of Education as suitable for 
the upper standards of elementary schools. The syllabus 
was divided into three parts, and the first of these is here 
dealt with. 

The course is well adapted for experimental work by indi- 
vidual children, and, as it forms a satisfactory introduction to 
the study of science, it is suitable for the lower forms of 
secondary schools as well as for pupils in the upper standards 
of elementary schools. 

Every teacher now understands the importance of practical 
exercises in all scientific instruction, however elementary. 
Unfortunately, it is not as yet always possible to provide 
accommodation and apparatus sufficient to enable individual 
pupils to experiment. This difficulty has been borne in mind 
in designing the form of the following lessons, each of which 
is divided into two parts — the first consisting of instructions 
for the performance of simple experiments, the second of 
explanations of the principles taught by the practical work. 

When circumstances permit, every child should perform the 
experiments, but when this is impossible the teacher should 



vi PREFACE. 

use the practical work as demonstrations before the class. 
The descriptive text will provide suitable reading lessons in 
class, or can be studied by the pupil at home. 

Our object has been to arrange a practicable and instruc- 
tive first course of science based upon sound educational 
principles. Most of the illustrations are new, and all of them 
have been inserted with the object of simplifying the text. 

For the advice readily given us, before we decided upon 
the plan of the lessons, by the late Mr. T. G. Rooper, M.A., 
one of His Majesty's Inspectors of Schools, Mr. J. A. Humphris, 
and Mr. Chas. Davis, we gladly take this opportunity of record- 
mg our thanks. 

R. A. GREGORY. 
A. T. SIMMONS. 



CONTENTS. 

LESSON PAGE 

/ ^ I. The Senses, i 

J X II- Matter and Hardness, ..... 6 

\,l \/ III. Solids, Liquids, and Gases, . . . . iq 

I s/ IV. Properties of some Common Things, - - 13 

V V. Properties of some Common Things — Continued, 16 

VI. Measurement of Length, 20 

VII. Measurement of Area, 24 

VIII. Measurement of Volume, 28 

y IX. Mass and Weight, 33 

/\ X. Measurement of Mass, 37 

. V'^ XI. The Principle of the Balance,- - . - 42 

XII. Density, 46 

XIII. Density — Continued, 51 

XIV. Determination of Density, - - - - 54 
XV. Things which sink in Water, - - • - 56 

XVI. Things which float in Water, - - - - 60 

XVII. Principle of Archimedes, 6d 

I QCVIII. Determination of the Density of a Solid, ■ 68 
'' vii 



viii CONTENTS. 

LESSON PAGE 

XIX. The Air around us, 71 

XX. The Pressure of the Air, - - - - 75 

XXI. Barometers, - - 79 

XXII. Why the Height of the Barometer alters, S3 

XXIII. Effects of Heat, 88 

. XXIV. Thermometers, - - 93 

XXV. Graduation of Thermometers. Fixed Points, 98 

XXVI. Soluble and Insoluble Solids, - - - 102 

XXVII. Soluble Liquids and Gases, - . . . 107 

XXVIII. There is no Loss during Solution. 

Evaporation, no 

XXIX. Saturated Solutions, 114 

XXX. Solubility of Things in Acids, - - - 116 

XXXI. Changes of Mass when Chemical Action 

i accompanies Solution, 120 

XXX H. Crystals and Crystallisation, - - - 124 

XXXIII. Crystals and Crystallisation— C(7«/m«ea', - 128 

XXXIV. Graphic Representation, ----- 133 
XXXV. Graphic Representation— C(7«//««t't/, - - 142 



r^ 



LESSON I. 

THE SENSES. 
PRACTICAL WORK. 

Things required. — A book. School bell. Bunch of flowers. 
Piece of sugar or salt. Smelling salts, or bottle of ammonia 
solution. A peeled onion, or any convenient substance with 
a strong smell. 
What to do. 

Notice the things on the table. You know they are there 
because you can see them. You could not see them in the 
dark. Eyes and light are necessary to see. 

Shut your eyes. You can now tell the things are on the 
table by feeling or touch. 

Stand away from the table and shut your eyes. You can 
now neither see nor feel the things, but you can smell some 
of, them, and therefore know they are in the room. 

Shut your eyes and let someone ring the bell. You 
cannot see or feel the bell, and cannot smell it, but you hear 
the sound and know that it comes from a bell. 

Taste the sugar and salt. You could tell one from the 
other by this means even if both looked and felt the same. 

REASONS AND RESULTS. 

How Science is Studied. — Before beginning any piece of 

work it is always best to find out all the things there are which 

we can use to help us in our task. If we neglect to do this it is 

quite possible we may find, when we have half finished our 

I. A e 



ELEMENTARY PHYSICS AND CHEMISTRY. 



labour, that had we remembered something which has escaped 
our notice, our task would have been easier and the result more 
satisfactory. 

It will be best for us, then, before we begin our study of this 
new subject, science, to make sure that we know all the ways of 
learning which it is possible to use. This may seem at first 
very difficult ; but, really, it is nothing of the kind, as we shall 
soon find out. Every boy or girl in the class will notice that 
there are several things on the table. How do you know that 
this is so ? Everyone of you has learned the fact in the same 
way. You say that you know there are things on the table 
because you see them, or, as some of you said, by seeing. But 
you must go a little farther. 

Seeing. — When can you see ? You are able to see when it is 
light and when your eyes are open. Even if it is light and your 
eyes are shut you cannot see. Or, if your eyes are open and it 
is dark you cannot see. Seeing is only possible when there is 
light and you have open eyes. But your eyes must be in a 
healthy condition. Some people with open eyes cannot see, 
because their eyes are unsound or diseased. They are called 
blind people. 

Feeling. — But though blind people cannot see they could still 
tell there were things on the table. Even when your eyes are 
shut you can quite easily find out the 
things you can no longer see. How do 
you manage it ? By feeling them or 
touching them. It would take you very 
much longer to learn all there is to be 
learnt about one of the substances on the 
table by feeling it than it does by seeing 
it. But if you were to practise this way of 
learning what a thing is like you would 
after a time become very clever at it. 
Blind people are clever enough to recog- 
nise their friends by feehng all over their 
faces. Though you generally feel with 
your fingers, the skin of all parts of your 
body is able to tell you when an object touches it. 

Smelling.— There are still other ways of learning about things. 




Fig. I. — Blind people 
can find tlieir way by 
feeling. 




THE SENSES. 3 

Even when you are in )-our places, away from the table, and not 

looking at it, you know that there is something unusual near 

you. You say there is a smell in the room. Two or three things 

on the table have a strong smell or 

odour, and by means of this you 

could be quite sure of their presence. 

Smelling' is another power you have 

which you will use in your studies 

of science. When you want to 

learn exactly what a smell is like 

you sniff the air up your noses from 

near the object which gives rise to Fig. 2.-Bloodhounds are very 

•' ... clever in nnding people by smell. 

the smell, and evidently it is by 

means of your noses that you are able to smell. Some animals, 
like the bloodhound, have this power to a great degree, and 
are very clever in finding the whereabouts of objects from 
their smell. In this way they used to be employed to find 
runaway slaves. 

Hearing. — If the bell on the table is struck you become aware 
of its presence through your ears. You hear the sound to which 
the bell gives rise. Or, if you drop the piece of sugar, or one of 
the other objects, after raising them from the table, the noise 
which results when the object strikes the table is quite enough 
to tell you that something is there. Hearing, a power which all 
people have who are not deaf, is another way of learning facts. 
Every day of your lives you make use of hearing in this way. 
Perhaps you know it is time to get up, because you hear the 
milkman shouting in the street, or because the alarum clock 
goes off, or someone calls you. You know a letter has arrived 
because of the postman's knock. You are sure there are birds 
in the trees because you hear them singing. You will be able 
to think of many other ways for yourself. 

Tasting. — Even yet you have not found all the ways by which 
you learn facts about the objects around you. A boy, who could 
neithw see, nor feel, nor smell, nor hear an object, might still 
be able to tell there was such a thing. This last power is very 
popular with boys and girls. Though you may shut your eyes 
and not be able to see, smell, or hear a lump of sugar, you could 
taste the sugar. 



4 ELEMENTARY PHYSICS AND CHEMISTRY. 

It is difificult to imagine anyone tasting- the sugar without 
feehng it, for while you taste the sugar you would also feel it on 
your tongue. But if you consider a httle you will think of cases 
where tasting is possible without feeling. In some towns, near 
factories or gasworks, it is often possible to taste things in the 
air though you cannot feel them. Some of you have tasted the 
salt in the air at the seaside. If you are very careful you may 
be able to taste the something in the air which causes the smell 
when the bottle of ammonia upon the table is opened. Often 
tasting and smelling go together ; many substances which have 
a taste also make themselves known by their smell. 

Seeing, Feeling, Hearing, Smelling, and Tasting are called 
" Senses." — These five ways of gaining knowledge, or of getting 
to know things, are called the senses. All ordinary persons 
possess them, and you must be sure to learn what they are. 
The first depends upon the eye, feeling upon the skin, hearing 
upon the ear, smelling upon the nose, and tasting upon the 
tongue. 

FIVE SENSES. 

1. Seeing depends upon the Eye. 

2. Feeling depends upon the Skin. 

3. Hearing depends upon the Ear. 

4. Smelling depends upon the Nose. 

5. Tasting depends upon the Tongue. 

The senses are sometimes called the five gateways of know- 
ledge ; and this is a very good name, for everything which you 
know has been learnt through one or other of these gateways. 

All the facts of science are learnt in the same way, and you 
cannot understand too soon that there is no difference between 
ordinary knowledge and science. In learning science you are 
only successful when you use your five senses very carefully, 
and this is only possible after they have been practised a great 
deal or trained sufficiently. You must learn to see properly or 
accurately, and to use each of your other senses without making 
mistakes. 

You Jiave, perhaps, when somebody has asked you how you 
know a certain thing, answered "By common sense." You have 
meant by this that you knew the thing by the use of your senses. 



THE SENSES. 5 

When you use your senses properly, without mistakes, what you 
learn is a fact of science. Or, as a great man once said, 
" Science is organised common sense." 

To BE Remembered. 
How Facts about Things are learnt. 

1. By Seeing. Eyes and light are necessary to see. 

2. By Feeling. Blind people can examine things by touch. 

3. By Hearing. When a boy hears the school bell he knows that 
there is a bell, though he may not see it. 

4. By Smelling. Smelling is assisted by sniffing. Bloodhounds can 
find men by following their scent. 

5. By Tasting. Usually accompanied by feeling ; often by smelling. 

These Powers are called "Senses." 

The parts of the body they depend upon are: (i) Eyes, (2) Skin, 
(3) Ear, (4) Nose, (5) Tongue. 

They are sometimes called "gateways of knowledge." 
There is no difference between science and ordinary knowledge. 
Everyone should train his senses carefully. 
Organised common sense is science. 

Exercise I. 

1. Name the five senses and the part of the body upon which each 
depends. 

2. Write down five things you can see, five things you can feel, five 
things you can smell, five things you can hear, and five things you can 
taste. 

3. What thing do you know ot which you can feel but not see ? 

4. Name some things you can see but which you can neither hear, 
feel, smell, nor taste. 



6 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON II. 
MATTER AND HARDNESS. 

PRACTICAL WORK. 

Things required. — Pieces of flint, rock-crystal, a tumbler, 
chalk, lead, pocket-knife, iron, copper, brass, wood, soap, wax, 
a turnip, carrot, potato, or apple. 
What to do. 

Notice that the things upon the table differ fram one 
another, and consider in what ways they are different. 
They differ in hardness, shape, size, and colour. 

Select one of the things, and notice that it will scratch 
some substances but not others. Test the things which 
the knife will scratch or cut and the things it will not 
cut. Test in the same way the things the finger-nail 
will scratch and those it will not scratch. 

Arrange the substances in pairs as below, so that one 
is scratched by the other. In this way a continuous table 
in which the substances are arranged according to their 
hardness can be drawn up thus : 

Fhnt scratches glass. Copper scratches lead. 

Glass „ iron. Lead „ chalk. 

Iron „ copper. Chalk „ wax. 

REASONS AND RESULTS. 

What is meant by Matter? — You must notice again to-day 
that there are several things on the table. You now know 
that you are sure of this fact by the help of your senses. 
Some of these things are recognised by more than one sense ; 
indeed some appeal to all of them. Many names are given 
to things which are studied by the help of the senses. Besides 
the name things, you can use the word substances, or the 
word which is perhaps most commonly employed, namely, 
matter. 



MATTER AND HARDNESS. 7 

You must not confuse this meaning of the word 'matter' 
with other meanings you have learnt. Most children, when 
the word is used, first think of the yellow fluid which pours 
out of a boil or gathering, but you must in these lessons, when 
the word matter is used, say to yourselves, that is the name 
given to all those things which are studied by means of the 
senses. 

There are many Kinds of Things. — There are many kinds 
of things about which you know through your senses. You 
would have no trouble in naming a great many of them. 
There are desks, books, wall-maps, slates, apples, bricks, and 
so on. When you begin to think about these things, it soon 
occurs to you that they are very different from one another, 
and that it would be much easier to study them if they were 
arranged in classes, putting those together which are alike 
and separating those which differ from one another. 

This is just what the headmaster does with the children 
who come to school. Because the boys who come differ from 
one another in many important ways, he cannot teach them 
altogether. Some can read very nicely, while others scarcely 
know their letters. Some can work out difficult sums, but 
others hardly know their tables. 

For these reasons, among others, the boys are arranged in 
classes or standards. So, if you wish to study all the kinds of 
things about you, you will find it best to learn how things 
differ from one another. You want, in fact, to learn the 
properties or qualities of at least the common things about 
you Then, when it becomes necessary, you will be able to 
imitate the headmaster and arrange things into classes in the 
manner already spoken about. This plan is called classifying 
things. You must, therefore, try to learn some of the properties 
of very common things. 

Things differ in Hardness. — If you were asked to say how 
the things on the table differ from one another, you would 
probably say that they differ in size, shape, colour, hardness, 
and in other ways. Now consider exactly what you mean by 
the property of hardness. A stone is hard, so is a piece of 
wood, and so is a piece of iron, but they are not of the same 
hardness. Some things, then, are harder than others. 



8 



ELEMENTARY PHYSICS AND CHEMISTRY. 




Fig. 3. — The things on the 
table differ in hardness as well 
as in other ways. 



It is often easy to decide which is the harder of two things. 
For instance, you know that a knife is harder than a piece of 
wood ; for you can often dig your thumb- or finger-nail into the 

wood, but you cannot dig your nail 
into a steel knife. Also, you can cut 
wood with a knife, but you cannot 
cut it with a piece of india-rubber, 
because the india-rubber is softer 
than the wood. All things which 
a knife will cut or scratch are softer 
than the knife, and all things which 
it will not cut or scratch are harder 
than it. 

In the same way, things like 
potatoes, some woods, chalk, bread, 
blotting paper, and soap can be 
scratched by the finger-nail, and 
are therefore softer than the finger- 
nail. Things like iron, glass, and 
flint cannot be scratched or cut 
by the finger-nail, and are therefore harder than it. 

The Test of Hardness. — You will now understand the way to 
find out which is the harder of two things. What has to be 
done is to test which will scratch or cut the other. If you were 
asked whether glass or flint was the harder, you should try it 
the flint will scratch the glass. It does. Will the glass scratch 
the flint ? It will not. Which is the harder then ? The flint, 
of course. 

In the same way, if you were given a large number of different 
things and told to arrange them in the order of their hardness, 
you would take any one of the substances and find which of the 
others it would scratch and which it would not scratch. Then 
another would be taken, and the same tests made, and so a list 
like the one below would be made. This is the method always 
adopted to find out if one thing is harder than another. 

1. Diamond. 5. Iron. 

2. Rock-crystal. 6. Copper. 

3. Glass. 7- Lead. 

4. Steel. 8. Wax, 



MATTER AND HARDNESS. 9 

The hardest substance is first in the list, the next hardest is 
second, and the softest is last. Any of the substances will 
scratch a substance lower in the list, and can be scratched by 
substances higher in the list. Diamond is seen to be the 
hardest substance ; it will scratch every other thing. Emery is 
also very hard, and is therefore used for polishing many things. 
The arrangement of things in the order of their hardness is 
similar to the arrangement of boys in a class. The top boy can 
beat all the other boys of the class in school-work ; and a boy in 
any position in the class can beat those below him, but can be 
beaten by those above him. 

To BE Remembered. 

Matter is the same as substances or things, and we learn about it by 
means of our senses. There are many kinds of things, but the same 
properties are possessed in a different degree by different things. 

TMngs differ in {a) hardness, {^) shape, (<) size, (</) colour. 

The hardness of a thing is its ability to resist being scratched or worn 
by another thing. 

Exercise II. 

1. Name six things around you. What name could you give them 
instead of things. 

2. WTiat have you learnt about the meaning of ' matter ' ? 

3. Why is it a good plan to divide things into classes ? 

4. Name as many ways in which things differ from one another as 
you can. 

5. What plan should you follow if you wished to arrange three sub- 
stances in the order of their hardness ? 

6. Which is the hardest thing you know ? What is it used for ? 



lo ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON III. 

SOLIDS, LIQUIDS, AND GASES. 

PRACTICAL WORK. 

Things required. — Some of the soHds used in the last lesson. 
Tea-cup, tumbler, salad-cream bottle, round medicine phial, 
piece of india-rubber tubing, and a large basin or pan of water. 
Water, milk, quicksilver, and any other liquids available. 
What to do. 

Notfice that the solid things upon the table are of different 
shapes, and that the shapes do not alter. 

Show by pouring the same amount of water or other 
liquid into different vessels that the shape of the water 
depends upon the shape of the vessel. 

Collect a bottle of ordinar}' gas, and use it to show that a 
gas has no surface and spreads itself through as much 
space as it can. The following is a way to do this : — 

Fill a bottle with water, and invert it in a basin of water; 
then displace the liquid with gas led from a jet by a piece 




Fig. 4. — Gas is issuing from the tube and bubbling up through 
the water in the bottle. 

of india-rubber tubing (Fig. 4). Now insert a cork into 
the neck of the bottle while it is still under water, or cover 
the mouth with a glass plate, and lift the bottle out of the 
water and place it on the table. The gas has the size and 
shape of the bottle. 

Open the bottle and wave it about; you immediately notice 



SOLIDS, LIQUIDS, AND GASES. n 

the smell of gas throughout the room, and know from this 
that the gas is everywhere in the room, and therefore has 
the size and shape of the room. 

REASONS AND RESULTS. 

Solids. — JNIost of the things you see around you have a certain 
size and shape of their own. The table in front of you and the 
desk you sit on have the same shape now as when they were first 
brought into the school, if no one has done anything to them. 
In the same way, a stone, a brick, a piece of india-rubber, or a 
tumbler keep their own shape unless someone breaks them. 
Things of this kind, which have a size and shape of their own, 
and remain of the same size and shape so long as they are not 
interfered with, are called solids. Some solids, as you have 
seen, are harder than others, and some can have their shape 
altered more easily than others. But none of them change by 
themselves. You know this very well in your own mind, though 
you may not have thought much about it. If you place a 
tumbler upon a table, and leave it for a while, you expect to find 
it there when you come back, and not changed into a bottle, 
because you know the shapes of solids do not alter unless some- 
one alters them. 

Liquids. — If you put a stone into a tea-cup, then into a 
tumbler, and then into a basin, you know that the size and 




Fig. $. — The shape of the liquid in these vcNsels is different, but 
the amount of Hquid is the same, and the surface is horizontal in each. 

shape of the stone remain the same in all the vessels. This is 
also true of any solid. But if a certain amount of water, say a 
wine-glassful, is taken and poured into a tumbler, you know that 
the water will not keep the same shape that it had at first. The 
water could be poured successively into vessels of different sizes 
and shapes, and finally into the wine-glass again ; but though 



12 ELEMENTARY PHYSICS AND CHEMISTRY. 

tJie shape would keep on altering^ being in every case the shape 
of the containing vessel, the size would remain unaltered. 
Things which behave in this way are called liquids. You can 
think of many liquids in use day by day. For instance, vinegar, 
oil, milk, beer, and lemonade are all liquids. 

There are other properties of liquids with which you are 
familiar. In the first place, the surface of a liquid at rest is 
always horizontal. You may shake the liquid up into a heap by 
jerking the vessel containing it, but as soon as you leave it 
alone it settles down again until its surface is horizontal. The 
fact that liquids can be poured from one vessel to another shows 
another property, namely, that liquids flow. A liquid can also 
be broken up into small round drops, such as the drops of water 
which form rain. 

Gases. — When a gas is spoken of, you think of the gas used 
to light rooms and streets. There are, however, many other 
gases, and you will perhaps learn about them some day. Some 
gases smell and some do not ; some are poisonous and some 
are harmless ; some, like coal-gas, will burn, and some will not. 
But all gases are alike in one respect ; they spread out and fill 
completely the vessel which holds them. A bottle of gas cannot 
be kept unless it is tightly corked, for after a while the gas 
escapes into the surrounding air. 

Comparison of the Size and Shape of Solids, Liquids, and 
Gases. — Solids, liquids, and gases are not alike as regards size 
and shape. Solids have a size and shape of their own, which 
differ for each solid, but remain the same for one particular 
solid. 

Liquids have a size of their own, but always take the shape of 
the vessel in which they are contained. 

(iases have no definite size or shape ; both these properties 
depend upon the space in which the gases are confined. How- 
ever small a quantity of gas may be, it always spreads out until 
something prevents it from taking up more space. 

To BE Remembered. 

Solids are things which keep their own size and shape. 
Liquids are things which take the shape of the vessel containing them, 
and have a horizontal surface when at rest. 



SOLIDS, LIQUIDS, AND GASES. 13 

Gases are things which completely fill any space into which they may 
be put. 

Exercise III. 

1. What do you know about the size and shape of solid things? 

2. What experiment would you do to show that while the size of a 
liquid remains the same its shape can keep on altering ? 

3. What do you know about the size and shape of gases? Describe 
an exfjeriment which shows what you say is true. 

4. State in your own words what a solid is, what a liquid is, and 
what a gas is. 

5. How do solids and liquids differ from one another ? 

6. In what important respects do liquids and gases differ ? 



LESSON IV. 

PROPERTIES OF SOME COMMON THINGS. 

PRACTICAL WORK. 

Things required.— Piece of glass, transparent liquids, sealing- 
wax, roll-sulphur, slate, lead, feathers, cork, sponge, sheet-lead, 
india-rubber, cane, air-ball, or pop-gun. 
What to do. 

Examine each of the things thoroughly, and consider 
what you would want to know about it in order to describe 
it to a person who had never seen it. 

Notice, for instance, that glass can be seen through 
(transparent), and breaks easily (brittle). 

Lead, and most other things, cannot be seen through 
(opaque). Lift the lead. It is heavier than pieces of the 
other substances of the same size (dense). Beat it into a 
thin sheet (malleable). Bend or twist it and it remains in 
the shape it is made (pliable). 

Stretch, bend, compress, or twist the india-rubber, and 
then release it. It goes back to the original shape (elastic). 



14 ELEMENTARY PHYSICS AND CHEMISTRY. - 

Compress an air-ball or a pneumatic tyre. Release it. It 
also springs back to the original shape ; hence air is elastic. 
Bend cane or whalebone (flexible). 



REASONS AND RESULTS. 

Common Thing's —Glass. — You must now take a few common 
things, and examine them to learn some of the properties things 
may possess. We will begin with Glass. What do you know 
about this substance ? You can see through it, you say. Yes ; 
and what do we call subst2nces which can be seen through ? 
Transparent ; that is right. All things you can see through are 
called transparent. Glass, then, is transparent. Some other 
things which are transparent are rock-crystal, air, water, and 
many other liquids. 

Now, if the plate of glass 13 dropped, what happens ? It 
breaks into pieces. What is a thing which breaks into frag- 
ments in this way called? Brittle. Some other brittle things are 
cast-iron, sticks of sealing-wax, roll-sulphur, slate. In being 
brittle all these things are like glass. In what way do they all 
differ from glass ? You cannot see through them, or, as is 
usually said, they are opaque. Opaque things, then, are those 
you cannot see through. 

Lead. — Now examine lead. What do you know about this 
substance? You say it is very heavy. But it is not enough to say 
that, for if you take a sufficient quantity of feathers they will 
weigh as much as the piece of lead. There is, of course, no 
difference between the weight of a pound of lead and a pound of 
feathers. What you meant to say was that a small piece of lead 
was very heavy. Because of this we speak of lead as being very 
compact or dense. Some other dense things are copper, gold, 
slate, etc. If a very large thing has but a small weight, it is not 
dense. Such things as cork, sponge, camphor, are not dense. 

What else do you know about lead ? You learnt in your last 
lesson that it is not very hard. It can be hammered out into 
sheets. Sheet lead is used for lining tea chests and other bo.xes. 
Solids which can be beaten out into sheets are called malleable. 
Copper, gold, platinum are all of them malleable, but gold has 
more malleability than any other solid. 



PROPERTIES OF SOME COMMON THINGS. 



55 



Can you learn anything more from your piece of lead? Yes, it 
can be bent and does not spring back ; its shape after bending 
or twisting remains just as you left it. All things which remain 
just as they are left after bending or twisting are called pliable. 
Copper, paper, and sheet-tin are also pliable. 

India-rubber. — Everybody knows the chief property of india- 
rubber, for the name of this property is actually given to 
india-rubber, which is made into long threads. These are called 
elastic. What is it about india-rubber which makes you say it is 
elastic ? Though you pull it, squeeze it, or bend it, it returns to 
its original shape and size when you leave it alone. It is the 
property of going back to its first shape and size after being 
forced out of it that is called elasticity. 




Fig. 6. — The india-rubber is stretched, but it goes back to its 
original length when it can, and is therefore said to be an elastic sub- 
stance. 



What Other elastic things do you know ? If you squeeze an 
air-ball or push upon a pneumatic tyre, when you remove your 
fingers they spring back to the shape they had at first. These 
experiments tell you that air is very elastic. Cane, steel, and 
whalebone all spring back when forced out of shape, that is, they 
also are elastic. But some things, such as a strip of whalebone 
and a cane, are only elastic to a great degree in one direction. 
Elastic things of this kind are generally called flexible. 



i6 ELEMENTARY PHYSICS AND CHEMISTRY. 

To BE Remembered. 

Glass can be seen through, or is transparent ; is easily broken, or is 
brittle. Opaque things cannot be seen through. 

Lead is heavy in comparison with the same bulk of many other sub- 
stances, or is dense ; is malleable, or can be beaten into thin sheets ; is 
pliable, or can be bent or twisted into different shapes. 

India-rubber is elastic, or returns to its original shape after the shape 
has been changed. Flexible things also return to their original shape 
after being bent. 

Exercise IV. 

1. What do you mean by a transparent substance and what by an 
opaque thing? Name six transparent things and six opaque things? 

2. Write down all you have learnt about lead. 

3. Explain as carefully as you can what you understand by a dense 
substance. Name several dense substances. 

4. What things are said to be malleable ? Write down the names of 
as many such things as you can. 

5. Why are india-rubber, air, whalebone, etc., said to be elastic? 
How would you show that air is elastic ? 



LESSON V. 

PROPERTIES OF SOME COMMON THINGS— 

Continued. 

PRACTICAL WORK. 

Things required. — Sponge, clean white blotting-paper,, glass- 
funnel, a cane. Crystals of rock salt and sugar candy, powdered 
salt and sugar. Several crystalline substances, such as washing- 
soda, borax, and rock-crystal. Some flour and soot. Matches, 
magnesium ribbon, and a taper. Some clay. 

What to do. 

Notice the holes or pores in sponge (porous). Place a 
sponge in a saucer of water, and notice that the water dis- 



PROPERTIES OF SOME COMMON THINGS. 



17 



appears ; it goes into the pores in the sponge, and can be 
squeezed out again. Filter water through blotting-paper, 
folded to form a cone, and placed in a funnel. Show that 
clay will hold water (impervious). 

Observe the regular shape of particles of salt and sugar 
(crystalline). Particles of flour or soot have no regular 
shape (amorphous). 

Add salt or sugar to water, and notice that it disappears 
(dissolves, or is soluble). 

Show that sand, slate-pencil, and many other substances 
are insoluble. 

Burn a match, paper, magnesium ribbon, etc. (combus- 
tible). Find some things which will not burn (incombus- 
tible). 

REASONS AND RESULTS. 

Sponge. — By squeezing a sponge you at once find out that it 
is elastic. But the first fact you notice about the sponge is that 




Fig. 7. — A sponge is very porous. 
when the sponge is placed in it. 



Water will go into the pores 



it has lots of holes in it. What other thing which is upon the 
table has holes in it ? The cane. But the holes in the cane are 
smaller than those in the sponge. What name do you give to the 
little holes spread over your skin ? Pores. A thing which is full 
of holes or pores is called porous. The sponge, therefore, is 
very porous. But for a thing to be porous it is not necessary 
to be able to see the holes. 

If you take a piece of blotting-paper, and fold it as shown in 
Fig. 8, put it into a glass funnel, and pour some water on it, the 
water finds its way through the paper because, though you cannot 
see them, there are holes in the paper, or it, too, is porous. 



i8 



ELEMENTARY PHYSICS AND CHEMISTRY. 



Even iron is porous to a small extent, and water is sometimes 
filtered through a certain kind of iron. Pumice, charcoal, sand- 




FiG. 8. — If a circular piece of paper is folded as shown by the dotted 
lines, it can be made into a cone which may be placed in a funnel for 
filtering. 

stone are also porous. In the kind of filter shown in Fig. 9 the 
water soaks through a block of carbon, and is thus purified. 
Things which will not allow water to pass 
or filter through them are called impervious. 
Clay is an impervious thing ; so is glass 
and india-rubber. 

Salt and Sugar.- — Salt and sugar are 

crystalline substances, that is, each small 

piece has a certain regular shape, which 

for a particular substance is always the 

same. Solids which take a regular shape 

like this are called crystals. You will learn 

more about these in a later lesson. Other 

common things which occur in crystals are 

washing-soda, borax, diamonds and some 

other precious stones, rock-crystal, and 

many other substances. 

Things which are not crystalline are called amorphous, a 

word which is made up of two Greek words meaning ' without 

shape.' Flour, soot, etc., are examples of amorphous things. 

Now, if you put the salt or sugar into a glass or bottle of water, 
and shake or stir the water, you will notice that the salt or sugar 
disappears, and if you taste the water you easily recognise the 
presence of the salt or sugar. You may say the salt or sugar has 




Fig. 9. —A Filter in 
which the water passes 
through a block of car- 
bon, owing to the porosity 
of the carbon. 



PROPERTIES OF SOME COMMON THINGS. 19 

dissolved or is soluble. Do you know any other soluble things? 
Tr\' some. You will find you can dissolve washing-soda, nitre, 
and borax in water, and in this way you prove they are soluble. 

Substances which will not dissolve in water are said to be 
insoluble. Many things are insoluble in water ; for instance, 
sand, gravel, slate-pencil, coal, chalk. However long you leave 
these in water they will not dissolve. 

Things which burn. — Many things easily burn in the air when 
made hot enough. If you hold a match in a gas-flame you can 
easily show that it continues to burn after taking it out. 
Similarly, you can make a piece of magnesium ribbon burn. 
Tapers and pieces of paper also burn quite easily. Things 
which burn in this way are said to be combustible. What are 
the common combustible tnings used ? Coal, coke, coal-gas, 
tallow, wood. Those substances which will not burn are called 
incombustible. Slate, iron, bricks, glass, etc., will not burn, and 
are therefore called incombustible things. 

' To BE Remembered. 

Sponge is porous, or contains numerous small holes or pores. All 
things are more or less porous. Things through which water will not 
pass are impervious. 

Salt and Sugar are crystalline, or are made up of little crystals, each 
ha\ang a certain regular shape ; they are soluble, or disappear when put 
in water. Particles of soot and flour have no regular shape, or are 
amorphous. 

Tilings whicli bum are combustible, and things which will not burn 
are incombustible. 

Exercise V. 

1. Many substances allow water to pass through them very readily. 
Why is this? What experiment would you perform to show this in the 
case of blotting-paper ? 

2. Write down all you know about sugar. 

3. What things are said to be soluble? Name six soluble things. 
What is the opposite to -soluble? 

4. What is the difference between combustible and incombustible 
things ? Name five things of each kind. 



20 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON VI. 

MEASUREMENT OF LENGTH. 

PRACTICAL WORK. 

Things required. — Foot-rule divided into inches on one edge, 
and into decimetres, centimetres, and millimetres on the other. 
Tape measure (or long rule) divided into inches and centi- 
metres. 
What to do. 

Notice the divisions upon the rule. Measure a few 
lengths, such as the width of a sheet of paper, or of a 
table, in feet and inches. Consider how confusing it would 
be if ihches and other standards of length had not a con- 
stant size. 

Notice the fractions of an inch, and find by measurement 
the number of inches in i-|- feet, 2^ feet, 2| feet, i yard, 
2 feet 9 inches, and any other lengths which may occur 
to you. 

Examine the metric divisions upon the rule. The 
smallest are millimetres ; ten millimetres make i centimetre, 
ten centimetres make i decimetre, ten decimetres make 
I metre. Notice that all these go in steps often. 

Find the number of inches which are equal to the length 
of I metre, the number of millimetres equal to an inch, and 
the number of centimetres equal to an inch. 

Measure a distance in inches and centimetres, and from 
the results determine the relation between the two. 

REASONS AND RESULTS. 

Measurement of Len^h. — Whenever you measure a length, 
what you do is to compare it with another length which is called 
the standard or unit. Every boy knows, from his lessons in 
arithmetic, that British people, when they speak of a length, 
express it as yards, feet, inches, or one of the other measures 



MEASUREMENT OF LENGTH. 21 

which have been learnt in Long Measure or Measures of 
Length. 

Most thoughtful boys have said to themselves at one time or 
another — What are these yards, feet, and so on? How does 
the maker of a rule know how long a yard has to be? And 
how is it that if you buy a yard measure in London, Manchester, 
or any other town, it is always the same length ? These are 
all ver>' important questions, and you must try to answer them. 

What a Yard is. — In the strong room of the Board of Trade 
in London there is a fire-proof iron chest which contains a bar 
of bronze. Into this bar, near each end, are sunk two golden 
studs, and across each stud fine lines are drawn. The distance 
between these marks (when the bar is at a certain temperature, 
called sixty-two degrees Fahrenheit, which you will understand 
before you get to the end of your book) is what is called the 
Imperial Standard Yard. Several exact copies of this bar have 
been made and are securely kept in different places. There is 
consequently very little danger of all the bars being burnt or 
lost at the same time. All yard measures should be the same 
length as the distance between these marks. The yard is 
divided into three equal parts, and each of these is called a 
foot. A foot is divided into twelve equal parts, and each part 
is called an inch. 

The Metre. — Lengths are not measured in yards, feet, and 
inches in all countries. In France, and most other countries, 
the standard length is what is called a metre. In Sevres, a 
bar of a similar kind to that kept by our Board of Trade is 
carefully preserved. The distance between the two marks in 
the golden studs is the standard known as the metre. The 
metre is longer than the yard. You know there are thirty-six 
inches in the ya.d, but the metre measures about thirty-nine 
and one third inches, or three feet, three and one-third inches 
(3 feet 3^ inches). This number is easily remembered because 
it only contains the figure 3. 

Divisions of the Metre. — The metre is not divided in the 
same way as the yard. A much better plan is adopted. First 
the metre is divided into ten equal parts, each of which is 
called a decimetre, so that you may write : 

10 decimetres make one metre. 



22 ELEMENTARY PHYSICS AND CHEMISTRY. 

The distance from one end to the other of Fig. lo is a 
decimetre. 

Next, each of these decimetres is divided into ten equal parts, 
each of which is a centimetre, and it takes one hundred of them 
to make a metre, consequently you may say : 

lo centimetres make i decimetre. 
ICO centimetres „ i metre. 

The distance from one number to the next in Fig. lo 
is a centimetre. 

Then, each centimetre is divided into ten equal 
parts, and each of these is called a millimetre, and it 
takes one thousand of them to make a metre. The 
smallest divisions in Fig. lo are millimetres. 

Thus, you see that you may write a table for the 
sub-divisions of the metre which you will have no 
trouble in remembering : 

lo millimetres make i centimetre 
ID centimetres „ i decimetre, 
lo decimetres „ I metre. 

For lengths greater than a metre the same simple 
plan is used. A length which contains exactly ten 
metres is called a dekametre ; one which just con- 
tains a hundred metres is called a hektometre ; and 
one which is exactly a thousand times as long as a 
metre is called a kilometre. These can be put to- 
gether in another little table : 

lo metres make i dekametre. 

lo dekametres „ i hektometre. 

lo hektometres ' „ i kilometre. 

Comparison of British and Metric Measures. — On 

the Continent the metric system of measurement 
is used almost entirely. The sign posts on the 
roads do not show how many miles it is to the next village 
or town, but the number of kilometres. Linen and silks and 
such materials are not sold by the yard, but by the metre, 
and shorter lengths are measured in centimetres. You will 
find it useful to remember ihat about 2^ or 2-5 centimetres 



MEASUREMENT OF LENGTH. 



23 



are equal to i inch, 3o"5 centimetres are equal to i foot, and 
eight kilometres are about five miles. 



Inches. 



















2 




3 


1 , , 1 1 


it, , ! . 


, 1 


1 


1 1 1 1 


1 III 


1 1 II 


nil 















12 3 4 5 6 7 

Millimetres. Centimetres. 

Fig. II. — An inch is very slightly longer than zj centimetres. 



To BE Remembered. 

A Standaxd Lengrth is required before lengths can be measured. 
The table of Long Measure shows how Britisli standards of length are 
related to one another. 

The Standard Yard is the distance between two lines upon a bronze 
bar kept by the Board of Trade. One tl.ird (^) of a yard is i foot, and 
one twelfth (xV) of a foot is i inch. 

The Metre is the French or metric standard of length. It is divided 
into tenths or decimetres, hundredths or centimetres, and thousandths or 
millimetres. The length of a metre is roughly 3 feet 3^ inches. 



Exercise VI. 

1. What is meant by the Imperial Standard Yard? Name the parts 
into which it is divided. 

2. What is a metre ? Compare its length with that of a yard. 

3. Explain how the metre is divided and write down the names 
which are given to these parts. 

4. What are some of the advantages of dividing the standard of 
length according to the metric system ? 

5. How many millimetres are there in each of the following :— 
centimetre, decimetre, and metre ? 

6. How many dekametres are there in a kilometre ? And how many 
netres in the same length ? 



24 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON VII. 
MEASUREMENT OF AREA. 

PRACTICAL WORK. 

Things required. — Square foot cut out of cardboard, and 

having square inches marked upon it. Square inch cut out of 

cardboard. Square decimetre of cardboard, having square 

centimetres marked upon it. Square centimetre of cardboard. 

What to do. 

Compare the square inch with the square foot. Count 
the number of square inches in one row marked upon the 
scjuare foot; there are 12. Count the number of rows; 
there are 12. The total number of square inches is there- 
fore 12 X 12 = 144. 

Compare the square centimetre with the square decimetre 
in the same way, and find the number of square centimetres 
there are in a square decimetre. 

Notice the difference of size of the square inch and the 
square centimetre. 

Find, by measurement, the number of square inches in any 
rectangular surface (such as a drawing board), and also tho 
number of square centimetres. This is done by multiplying 
the length of one side by the length of the side at right 
angles to it 

By comparing the two results, determine roughly the 
number of square centimetres in a scjuare inch. 

REASONS AND RESULTS. 

Measurement of Area. — Most of the boys who read this book 
will probably already know the difference between lengths and 
areas. But to make quite certain we will take a few simple 
examples. 

Provided with a rule, it would be easy to measure the length 
of the room and its breadth or width. If we had a ladder 



MEASUREMENT OF AREA. 25 

we could, in the same way, measure its height. Now, if we 
were going to have a carpet put down, we should give the 
upholsterer the order, and he would pay us a visit to measure 
the floor. You know very well it would not be enough for 
him to measure the length of the room only, or its width 
only, because both of these are measures of length. To know 
how much carpet he wants the workman must find out the 
amount of surface the floor has, or what is called its area. To 
do this he measures both the length and width of the floor, and 
when he multiplies them together he gets the area, if the room 
is a square or oblong one. If he measures the length and width 
in feet, then by multiplying them together he gets the area of 
the floor in square feet ; if the measurement of the length and 
width were taken in inches, the area in square inches would be 
obtained by multiplying them together. 

Whenever areas are measured in this country, square inches, 
square feet, square miles, or some other unit from square 



Fig. 12. — This shows how a square yard can be divided into square 
inches. Each small square represents a square inch, and the large 
squares bounded by thick lines represent square feet. 

measure is employed. 'Square measure' is obtained from 'long 
measure' by multiplying. Thus, as there are 12 inches in a 



26 ELEMENTARY PHYSICS AND CHEMISTRY. 

foot, there are 12x12 square inches in a square foot. You 
will understand this by examining Fig. 12. Each of the large 
squares bounded by thick lines represents a square foot, but it 
is of course smaller than a real square foot. 

Square Measure.— By referring to Fig. 12, which illustrates 
how a square yard may be divided into square feet and square 
inches, and examining the squares of cardboard divided into 
square inches or square centimetres, it is easy to see how square 
measure is obtained from long measure. We will write what we 
have learnt in the form of a table : 

144 ( = 12 X 12) square inches make i square foot. 
9 (= 3x 3) „ feet ,, i „ yard. 

3oH = 5*x5i) „ y-ii-ds „ I „ pole. 
How many square inches are there in a square yard ? You can 
find out by counting the squares in Fig. 12, or by counting the 
squares in one of the areas representing a foot and multiplying 
the number by nine. 

Square Metric Measures.— If instead of measuring the length 
and breadth of the floor in feet the workman had measured 
them in metres or decimetres, what would the area obtained by 
multiplying be measured in ? Not in square feet, but in what is 
called square metres, square decimetres, etc. Square measure 
in the metric system is obtained from long measure in just the 
same way as we used in the case of inches. All we mean by 
the metric system is the plan of using metres, etc., instead of 
yards, etc., in measurements of all kinds. We can now write 
down the measures of area or surface in the metric system : 

100 (= lox 10) square millimetres make i square centimetre. 

100 (=10x10) „ centimetres „ i „ decimetre. 

100 ( = 10x10) „ decimetres „ i „ metre. 

A square decimetre is too large to be shown on this page. 
Fig. 13 shows two complete rows of square centimetres, but 
there are ten rows of this kind in a square decimetre. The 
square centimetre AGFE in the top left-hand corner is divided 
into square millimetres. As i square centimetre contains 100 
square millimetres, i square decimetre or 100 square centi- 
metres contains 100 x 100 square millimetres, that is 10,000 
square millimetres. 



MEASUREMENT OF AREA. 



27 




The size of a square centimetre is compared with the size of a 
square inch in Fig. 14. You will see that a square inch is much 
larger than a square centimetre. Each A E B 

side of the square inch is 2 '54 centi- 
metres in length, so the number of 
square centimetres in a square inch _^ 
is 2'54 X 2"54 — 6'45 or nearly 6h square 
centimetres. 



To BE Remembered. 

Area is found by measuring length in two 
directions. A foot square is a square which 
has each side one foot in length. Square 
Measure is derived from Long Measure ; it 
tells the standards which nnist be used in 
measuring areas. 

Square Inches and Square Centimetres. 
— As 2 '54 cm. = I inch, the number of 
square centimetres in i square inch is 
2'54 X 2"54 = 6'45, or -\-ery nearly 6i square 
centimetres. 

Exercise VII. 

I. Wbat measurements of a wall must we 
know before we can tell how much paper 
will be required to cover it ? 



F 



Fig. 14. — A sciu.ire incli conuiins 6"45 
square centimetres. 



Fig. 13. — Square centimetres 
and square millimetres. Ten rows 
of ten square centimetres make 
one square decimetre. 



2. How many square inches are there in a square foot, and how many 
in a square yard ? 

3. How many square centimetres in a square metre, and how many in 
a square decimetre ? 

4. How many square millimetres in a square decimetre? How n..iny 
square millimetres in a square metre ? 



28 ELEMENTARY PHYSICS ^ySID CHEMISTRY. 

LESSON vni. 

MEASUREMENT OF VOLUME. 
PRACTICAL WORK. 

Things required. — A box one cubic foot in size, and having a 
lid one inch thick. The box should be a cubic foot with the lid 
closed. The top of the lid should be divided into square inches, 
and lines round the edge should mark off cubic inches (Fig. 15). 
Lines should be drawn round the box at every inch from the 
bottom edges. Cubic inch of wood. Cubic centimetre of wood. 
Slab of wood 10 x 10 x i cm. Rod of wood i x i x 10 cm. A box 
measuring inside exactly i decimetre high, i decimetre wide, 
and I decimetre long, that is, i cubic decimetre internal volume 
(Fig. 16). Litre and half-htre measures ; also pint and half-pint. 
What to do. 

Notice that the area of each face of the cubic foot is one 
square foot. Count the number of square inches marked on 
the top of the lid. Notice that the cubic inch has the same 
thickness as the lid, and that 144 cubic inches could be cut 
out of the lid. Shut the lid and stand the box upside down 
on the table. You know how many cubic inches there are 
in the slab which forms the lid. How many slabs of the 
same thickness are marked upon the box, and how many 
cubic inches are there altogether in a foot cube ? 

How many cubic centimetres are there in the rod of v/ood? 
How many such rods would be required to make a slab of 
wood the same size as that supphed ? How many cubic 
centimetres, therefore, does the slab contain? How many 
slabs would be required to fill the box? How many cubic 
centimetres would go into the box ? 

Compare the cubic centimetre with the cubic inch and 
the cubic decimetre with the cubic foot. Knowing that 
2"54 cm. = I inch, calculate the number of cubic centimetres 
in one cubic inch. 



MEASUREMENT OF VOLUME. 



29 



Notice the difference between one litre (the capacity of 
one cubic decimetre) and one pint, and determine roughly 
the number of pints in one litre. 

REASONS AND RESULTS. 

Measurement of Volume. — If we examine Fig. 15, which repre- 
sents a cubic foot, and bear in mind what we have already 




Fig. 15.— Each little cube at the top may be imagined to be i cubic 
inch. There are 144 of them. Twelve such layers of cubic inches make 
I cubic foot. 



learnt, we shall easily understand that each edge of the solid 
there represented is measured as a length. Each of its faces has 
an area, which can be obtained by multiplying together the 
lengths of two of the edges which meet at a corner. But the 
size of the solid, or the amount of room it takes up, or the space 
it occupies, is quite a different thing. This new measurement 
is what is called its volume. 

The volume of a solid body is obtained by measuring in 
three directions. Just as to find the area of a surface we 
measure its length and breadth, so to measure the volume of 



3° 



ELEMENTARY PHYSICS AND CHEMISTRY. 



a solid we must find in addition to measurements of length 
and breadth, another distance called the thickness. If we 
multiply length, breadth, and thickness together we obtain a 
volume or cubical content. 

Returning to our cubic foot for a moment, let us find how 
many cubic inches it contains. We know already that any one 
of its faces covers 144 square inches of surface. In the cube we 
can think of a layer of 144 cubic inches, or little cubes each edge 
of which is an inch, and each face of which is a square inch. 
How many such layers are there in the whole cubic foot? 
Evidently there are twelve layers. 

Consequently, in the whole cube we have 144x12 = 1728 
little cubes whose edges are one inch long and whose faces 
are each one square inch in area. Or one cubic foot contains 
1728 cubic inches. 

We could reason in the same way to find out how many 
cubic feet are required to build up a cubic yard. We may write 
down, therefore, 

1728 ( = 12 X 12 X 12) cubic inches make i cubic foot. 
27(= 3x 3X 3) „ feet „ i „ yard. 

Metric Measures of Volume. ^ — We proceed in a similar way 
when we wish to measure volumes by the metric system. Ten 




Fig. 16. — Ten cubes like A would make a rod like B. Ten rods like 
B would make a slab like C, and ten such slabs would go into the box D. 



cubic centimetres in a row would make a rod as at B in Fig. 16. 
Ten such rods would make a slab as at C, which would 
therefore contain 10x10 cubic centimetres, that is, 100 cubic 



MEASUREMENT OF VOLUME. 31 

centimetres. Ten such slabs would go into a box such as is 
shown at D ; so the number of cubic centimetres in a box this 
size would be 100x10 cubic centimetres, that is 1000 cubic 
centimetres. 

The box measures 10 centimetres each way, and its volume 
is a cubic decimetre. You know there are 10 centimetres 
in a decimetre, so you may say the edge of the decimetre 
box is 10 centimetres in length ; the area of one of its faces 
IS 10 X 10=100 square centimetres ; its volume is lox lox 10 = 
100 X 10= 1000 cubic centimetres. 

The Litre. — If a hollow cube is made i decimetre long, 
I decimetre broad, and i decimetre deep, it will hold 1000 




Litre. Pint. 

Fig. 17. — A litre bottle will hold ij pints. These two bottles look 
nearly the same size, but the glass of the litre bottle is much thinner 
than that of the pint bottle. 

cubic centimetres of liquid. This capacity is called a litre. All 
liquids are measured in litres in countries where the metric 
system is adopted. Thus in France, wine, milk, and such 
liquids are sold by litres instead of by pints. A litre is equal 
to about one and three-quarters English pints. A litre bottle 
and a pint bottle are shown side by side in Fig. 17. 



32 ELEMENTARY PHYSICS AND CHEMISTRY. 

We may now write some of the measures of volume in the 
metric system : 

ID centihtres make i decilitre. 

lo decihtres „ i litre (looo cubic centimetres). 

lo Htres „ i dekahtre. 

lo dekahtres „ i hektolitre. 

lo hektohtres „ i kilolitre or i cubic metre. 

Cubic Centimetres and Cubic Inches. — It has already been 
found that one inch is 2*54 centimetres long. The area of one 




Fig. 18. — It takes i6J cubic centimetre? to make i cubic inch. 

square inch, that is of a surface i inch long and i inch broad, 
is therefore 2*54 x 2*54 or 6'45 square centimetres. The volume 
of a cubic inch, if the measurements are made in centimetres, 
is 2"54X2'54X 2-54 cubic centimetres, that is i6-38 cubic centi- 
metres. It would thus take i6"38 cubic centimetres, or roughly 
16^ cubic centimetres, to make one cubic inch. Sixty-one cubic 
inches are about equal to the volume of one decimetre. 

To BE Remembered. 

Volume is cubical content. Length, breadth, and thickness have to 
be measured in determining volume. Cubic Measure is derived from 
Long Measure. 

A Litre is a volume or capacity of I cubic decimetre, that is, 1000 
cubic centimetres ; i litre = if pints. 

As 2'54 centimetres = I inch, the number of culiic centimetres in 
I cubic inch is 2-54 x 2-54 x 2*54= 16*38. 



MEASUREMENT OF VOLUME. 
Exercise VIII. 



33 



1. If you were told the number of inches in a foot, how would you 
calculate the number of cubic inches in a cubic foot ? 

2. What is meant by a litre? What would be the length of the side 
of a cube which contained looo litres ? 

3. Write down the names given to the parts of a litre. 

4. Which would hold more water, a litre jug or a pint bottle ? 



LESSON IX. 



MASS AND WEIGHT. 



PRACTICAL WORK. 

Things required.— The two pieces of iron or brass which in 
ordinary language are called a " pound " and a " half-pound " 
weights ; or a " pound " and a " two-pound " will do. Also set 
of ounce " weights." Pair of scales. Spring balance. A yard 
of thin iron wire. Strong magnet. Equal masses of lead and 
cotton wool. 
What to do. 

Lift the two pieces of metal. One feels heavier than the 
other, that is, the masses 
are different. 

Place a certain amount 
of lead in one pan of a 
balance, and counter- 
poise it with cotton-wool 
in the other pan. The 
masses are equal but the 
volumes are different 
(Fig. 19). 

Drop one of the pieces 
of metal ; it falls to the 
ground on account of 
the earth's pull upon it. 
I. 




lib or COTTONWOOL 



Fig. 19. — I lb. of lead has the same ma.^s 
as I lb. of cotton wool. 

If the attractive force were 



34 



ELEMENTARY PHYSICS AND CHEMISTRY. 



doubled when you held the ]iiece of metal, what difference 
would you feel ? If the attraction suddenly ceased, what 
would happen when you released your hold of the piece 
of metal ? 

Wind a piece of iron wire round a smooth walking stick 
or a round ruler, and so make a coil. Hang one end of 
the coil on a support, and to the other attach the iron 
pound. Observe that the spring is made longer by the 
downward pull of the iron (Fig. 20). 

Examine the parts of (^% 

a spring balance (Fig. jx 

21). Attach one ounce 

to the balance and 

show that the marker 

is pulled down to the 

division i. The pull of 

the spring upwards and 

of the ounce downwards 

are equal. 

If possible, using a 

delicate spring balance, 

such as is used for 

weighing letters, show 

that the downward pull 

of a mass of iron can 



Fig. 20. — The coiled 
spring is pulled out by 
tne mass hung from it. 



Fig. 21. — To 
show the spring 
inside a spring 

be increased by holding balance. 



a strong magnet beneath it (Fig. 22). 



REASONS AND RESULTS. 

What Mass is. — Before we attempt to learn how mass is 
measured we must know what is meant by this word. When 
we say that the mass of one piece of metal is twice as great as 
the other, we mean that one of them contains twice as much 
iron, brass, or other material as the other. And always when 
we speak of the mass of a body we mean the amount of stuff 
or matter, of whatever kind, it contains. Though the masses 
of two lumps of material may be equal, as can be shown by 
making one balance the other in a pair of scales, their volumes 



MASS AND WEIGHT. 



35 



may he very unequal. This is very well seen by comparing 
equal masses of lead and cotton-wool. 

The mass of a thing is not the same as its weight, though 
one is often confused with the other. Keeping in mind what 
is meant by mass, we can, by doing 
one or two experiments, find out 
exactly what should be meant when 
tlie word weight is used. 

Mass is not Weight. — If the mass 
of a pound is dropped from the hand 
it falls to the ground. If the same 
mass is hung upon the end of a coil 
of iron wire, the coil is made longer 
by the downward pull of the mass 
fixed to its end. The amount by 
which a steel spring is lengthened, 
as the result of such downward pull 
of masses attached to its end, is used 
to measure their weights in the in- 
stiaiment called a spring balance. 
If we use a ver)^ delicate balance 
of this kind, like those used in 
weighing letters, we can make the 
weight of a small piece of iron hung 
on to the balance appear greater by 
holding a strong magnet beneath it. 
But though the weight may appear 
greater, the mass or quantity of 
matter is, of course, the same whether 
the magnet is under the iron or not. 

If you have understood these ex- 
periments you will have no trouble 
in seeing clearly what exactly is 
meant by the weight of a body. 
Unsupported things fall to the 
ground ; a fact which can also be expressed by saying that 
they are attracted to the earth. Now, even when they are 
supported, like the objects on the table, the earth attracts 
them just as much, only the table prevents them from falling, 




Tir,. 22. — The piece of iron 
may be made to appear heavier 
by a magnet, but the mass does 
not change. 



36 ELEMENTARY PHYSICS AND CHEMISTRY. 

as they would do if there were no table there. The force with 
which a body is attracted by the earth is its weight. But it 
must be remembered that this force is just the same whether 
they actually fall to the ground or not. You become aware 
of the weight of a heavy thing when you hold it on the out- 
stretched hand. You feel that it is only by using your strength, 
or as it is sometimes said, by exerting force, that you prevent 
it from falling. This force which you exert is equal to the 
weight of the heavy object. If you have understood this, and 
it is necessary that you should, you will never confuse mass 
and weight, for while mass is the amount of substance in a 
thing, weight is the force with which the thing tries to get 
to the earth. 

To BE Remembered. 

The mass of a thing and its weight are not the same. 

The mass of a thing is the quantity of matter in it, and this remains 
the same wherever the body is placed. 

The weight of a thing is the strength of the earth's pull upon it. In 
other words, it is the force with which the thing is attracted by the 
earth. 

Exercise IX. 

1. What do you mean by the mass of a thing? Is there any differ- 
ence between the mass of a pound of cotton-wool and the mass of a 
pound of iron ? 

2. Which is larger in size, the mass of a pound of cotton-wool or 
the mass of a pound of iron ? 

3. What experiments would you perform to show that masses are 
attracted by the earth ? 

4. What do you mean by the weight of a mass? Write down the 
difference in the meaning of {a) the mass of a book ; (3) the weight of 
a book. 

5. It is possible to make the weight of a piece of iron appear greater 
than it really is. How would you do it ? 



MEASUREMENT OF MASS. 37 

LESSON X. 

MEASUREMENT OF MASS. 
PRACTICAL WORK. 

Things required. — Examples of British masses, e.g. an ounce, a 
pound, a half-hundredweight. Box of metric masses, generally 
spoken of as a box of " weights." A kilogram. Spring balance. 
What to do. 

Compare the pound and the kilogram. Hang the 100 
gram mass from a spring balance, and notice that the 
downward pull or its weight is equal to the weight of 3^ 
ounces. 

What then is the British equivalent of the weight of a 
kilogram ? It is evidently equal to the weight of 3^ ounces 
X 10= weight of 35 ounces = the weight of 2\ lbs. (roughly). 

REASONS AND RESULTS. 

Measurement of Mass. — Just as in measuring lengths we 
found it was necessary to have a standard with which to com- 
pare, so in measuring mass we must also have a standard or 
unit. Then we can say how many times the mass of a given 
body is greater or smaller than our unit. In this country the 
standard of mass is the amount of matter in a lump of platinum 
which is kept with the standard yard by the Board of Tiade. 
This lump of platinum is called the imperial standard pound 
avoirdupois (Fig. 23). The divisions, etc., of the imperial pound 
you have already learnt in your arithmetic lessons, under the 
name of "avoirdupois weight." 

A mass of i lb. avoirdupois is kept at a weights and measures 
office in every city, so as to test the lb. 'weights' used by trades- 
men, and see whether they really have the mass of i lb. or are 
too light. A local standard lb. used for this purpose is shown 
in Fig. 24. 



38 



ELEMENTARY PHYSICS AND CHEMISTRY. 



AVOIRDUPOIS WEIGHT.i 



1 6 drams 
i6 ounces 
28 pounds 

4 quarters 
20 hundredweights 



make i ounce. 
„ I pound. 
„ I quarter. 
„ I hundredweight. 



I ton. 



The Kilogram and Gram. — The standard of mass which is 
adopted in France, and in other countries where they use the 




Fig. 23.— Exact size and shape of the British standard pound, made 
of platinum. From Aldous's Course of Physics (Macmilian). 

metric system, is called the kilogram. The kilogram is the 
amount of matter in a lump of platinum which is kept in safety 
at Sevres. This standard is bigger than the British pound ; 
indeed it is equal to about two and one-fifth of our pounds. 
It is very interesting to know how the mass of a kilogram was 
obtained. It was agreed to give the name gram to the mass 
of water which a little vessel holding one cubic centimetre would 
contain.^ The lump of platinum was made equal to the mass 

1 Remember this is a wrong use of the word weight. What ought it to be? 

2 The temperature being 4° C. But it is unnecessary for the beginner at 
this stage to consider why the temperature must be mentioned. 



MEASUREMENT OF MASS. 39 

of one thousand cubic centimetres of water ; it would therefore 
have the same mass as one thousand cubic centimetres of water, 
or, as you know this amount is called, a litre of water. The 



Fig. 24.— Size and shape of the avoirdupois i lb. kept by In- 
spectors of Weights and Measures. Made of brass. From Aldous's 
Course of Physics (Macmillan). 

names used for the divisions, etc., of the gram are obtained in 
the same way as in the case of the metre, thus : 

METRIC MEASUREMENT OF MASSES. 

10 milligrams = i centigram. 10 grams = i dekagram. 

10 centigrams = i decigram. 10 dekagrams = i hektogram. 

10 decigrams = i gram. 10 hektograms= i kilogram. 



40 



ELEMENTARY PHYSICS AND CHEMISTRY. 



How to remember Metric Measures. — As we have now 

described the metric measures of length, volume, and mass, 

this is the place to explain how they can all be easily 
remembered. 




Fig. 25. — Exact size and shape of the metric standard of mass — the 
kilogram — made of platinum. From Aldous's Course 0/ P/i_yszcs {Ma.c- 
millan). 

You should bear in mind that in metric measures 



milli- 


means 


thousandth. 


centi- 




hundredth. 


deci- 




tenth. 


deka- 




ten times. 


hekto- 




a hundred times. 


kilo- 




a thousand times. 



By putting these words in front of the words metre, litre, and 
gram, all the metric measures of length, volume, and mass are 
obtained, as shown in the following table : 



MEASUREMENT OF MASS. 



41 





Length. 


Volume. 


Mass. 




Milli-metre 


Milli-litre 


Milli-gram 


T(i^ 


Centi-metre 


Centi-litre 


Centi-gram 


A 


Deci-metre 


Deci-litre 


Deci-gram 


I 


Metre 


Litre 


Gram 


10 


Deka-metre 


Deka-litre 


Deka-gram 


100 


Hekto-metre 


Hekto-litre 


Hekto-gram 


1000 


Kilo-metre 


Kilo-litre 


Kilo-gram 



You see from this that what you have learnt to call the metric 
system of weights and measures is much simpler than ours, 
and the boys in countries where it is used have not to learn so 
many different tables as they have in England when they begin 
" weights and measures " sums. 



To BE Remembered. 

The British standard of mass is the imperial pound avoirdupois. 

The metric standard of mass is the kilogram ( = 2^ lbs.), or the 
mass of 1000 cubic centimetres of water at a certain degree of tem- 
perature. A gram is the mass of i cubic centimetre of water. 

To remember metric measures bear in mind the words milli 
(thousandth), centi (hundredth), deci (tenth), deka (ten), hekto (hundred), 
kilo (thousand). 

Exercise X. 

1. ^Miat is the standard of mass in British countries and what in 
France ? 

2. Write out "avoirdupois weight." 

3. State exactly what a kilogram is. How much water by volume 
has a mass of a kilogram ? 

4. Write down the table you have learnt of the metric system of 
masses. 



42 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON XI. 

THE PRINCIPLE OF THE BALANCE. 

PRACTICAL WORK. 

Things required. — Lath with a ring or eye screwed into one 
edge, above the centre, and a similar ring at each end ; the lath 
should be marked in equal divisions of about i centimetre, 
starting from the centre. Two pill boxes, or shallow trays, 
having threads for suspending them from the lath, i lb. of 
very small nails. Set of " weights." 
What to do. 

Hang the lath from a smooth round nail by means of 
the ring above its centre, so that it turns easily about the 
nail and hangs horizontally, as it will do if properly sus- 
pended. Hang a mass by means of thread upon the lath 
at any convenient distance on one side of the nail, and 
balance it with a mass of the same amount on the other 
side. Measure and prove that the distance of the masses 
from the middle division is the same in each case. 



. •I n i 1 I I I iVi I I I I I rT-n-r> y «< XTTT 




Fir,. 26. — A balance made with a Fig. 27. — The mass multiplied 

lath and pill-boxes. by the distance from the turning 

point gives the same result on both 
sides. 

Using the lath as before, hang over it, at equal distances 
from the nail, two pans (which you can make out of pill 
boxes and thread), one on each side of the nail. Put a 
known mass, say 20 grams, or, if more convenient, an 
ounce, in one pan and find out what mass must be placed 
in the other for the lath to be horizontal, or, as we say, for 
the lath to be equilibrium. Prove in this way that when 



THE PRINCIPLE OF THE BALANCE. 43 

the pans are at equal distances from the support there is 
equihbrium when the masses are equal. 

Hang two masses, one twice as great as the other, on 
opposite sides of the turning-point of the lath. Move them 
along until they balance one another ; then notice that the 
smaller of the two masses is twice as far away from the 
centre as the larger. Experiment with other masses, and 
show that in every case 

mass its distance mass its distance 

on X from turning- = on x from turning- 
one side point other side point. 

Find in this way the masses of a few things, such as 
half-a-crown, penny, etc. 

REASONS AND RESULTS. 

The Principle of the Balance. — When two boys are going to 
have a see-saw they first place the plank upon a log or some 



Fig. 28. — The bigger boy sits nearer the log than the smaller boy t» 
make the balance right. 

Other support, so that it balances, half of it being on one side of 
the log and half on the other. If the boys have the same mass 
they sit at equal distances from the log, and then the see-saw 
moves easily up and down. If one boy is bigger than the other, 
he sits nearer the log than the smaller boy in order to make the 
balance right. A small boy at one end of the see-saw can 



44 ELEMENTARY PHYSICS AND CHEMISTRY. 

balance a big and heavy boy sitting near the log upon the other 
side. 

A small lath balanced upon a ring above the centre, as shown 
in Fig. 26, is similar to a see-saw, and, like it, will swing up and 
down. If a certain mass is hung from one side, then the same 
mass must be hung at the same distance from the centre on 
the other side in order to balance the lath. When the lath is 
supported at the middle, equal masses are always balanced at 
equal distances from the point of support. This fact is made 
use of in constructing ordinary balances or scales. A simple 
form of balance can be made by hanging two pill boxes from 
hooks at the ends of the lath, as shown in the picture (Fig. 26). 

The Balance. — The form of balance shown in Fig. 29 is 
evidently similar in principle to the supported lath with pill 





Fig. 29. — A simple balance, or pair of scales. 

boxes. This kind of balance is good enough for ordinary pur- 
poses, but when exact weighings are wanted, a better form, 
such as that shown in Fig. 30, is used. All the parts in this 
balance are very carefully made, and the greatest possible pains 
are taken to have very delicate supports and accurate adjust- 
ments. Instead of the wooden lath described just now, a brass 
beam, AB, is employed. This is supported at its middle line 
on a knife edge of hard steel, which, when the balance is in use, 
rests on a true surface of similar steel. The hooks to which the 
pans are attached are likewise 'provided with a V-shaped groove 
of hard steel, which also, when the balance is rn use, rests upon 
knife edges on the upper parts of the beam. To the middle of 
the beam is attached a pointer, F, the end of which moves in 



THE PRINCIPLE OF THE BALANCE. 



4S 



front of an ivory scale, G, fixed at the bottom of the upright 
which carries the beam. When not in use, the beam and hooks 
are Hfted off the knife edges by turning the handle C. 




Fig. 30. — A delicate balance for the accurate determination of masses. 



The Balance is used for comparing Masses — When we wish 
to know the mass of any body we place it in one pan of the 
balance (for the sake of convenience the left one is geneially 
used), and then we counterpoise it with known masses. From 
our second experiment with the suspended lath we know that 
when the body whose mass is required is balanced by one or 
more masses from a box of standard masses, called a box of 
" weights," we can find the unknown mass by adding together 
that of all the masses in the right hand pan. 

To BE Remembered. 

A balanced lath remains in equilibrium when the mass on one side, 
multiplied by its distance from the turning-point, is equal to the mass 
on the other side, multiplied by its distance from the turning-point. 

The balance is used to compare masses. The principle upon which 
it depends is, that when two mas.ses placed at the same distance on 
opposite sides of the turning-point balance one another, they are equal. 



Exercise XI. 

I Describe an experiment to illu.strate the principle of the balance, 
and give a sketch of the things you use. 



46 ELEMENTARY PHYSICS AND CHEMISTRY. 

2. Describe, with a sketch, the construction of the balance, and 
explain its use. 

3. If a boy whose mass is 56 lbs. sits on one side of a balanced see- 
saw, at a distance of 6 feet from the log upon which it rests, how far 
from the log must a boy whose mass is 1 1 2 lbs. sit in order to keep the 
see-saw level ? 

4. Why is it necessary to be sure that the pans of a balance are sus- 
pended at the same distance from the turning-point? 

5. Suppose a tea merchant uses a pair of scales having a beam not 
supported from the centre, but from a point a little distance nearer the 
pan in which he puts his "weights." Do his customers get fair weight? 
If not, explain whether they get less or more than they ought. 



LESSON XII. 

DENSITY. 

PRACTICAL WORK. 

Things required. — Cubic centimetres of oak, lead, cork, 

and marble. Two 4 oz. flasks, or small bottles of the same 

size. Balance and box of " weights." Graduated glass jar, 

marked in cubic centimetre divisions (Fig. 31), pipette. Small 

beaker. 

What to do. 

Determine, by means of a balance, the mass of each 

of the cubic centimetres supplied, and record the results 

thus : 

Grams. 

Mass of the cubic centimetre of wood (oak) = 
„ „ „ lead = 

„ „ „ cork = 

„ „ „ marble = 

Counterpoise two small bottles of the same size. Fill 
one with water and the other with methylated spirit. 
Notice that the bottle of water is heavier than the bottle 
of spirit, though the volume of each liquid is the same. 
Place a glass vessel in one pan of the balance, and counter- 
poise it with shot or small nails in the other. Measure out 





•82 = 


U 


I 


•.35 = 


11-^- 




•24 = 


_6 
25 


2 


•84= 


2fi 



DENSITY. 



47 



loo cubic centimetres of water into the glass vessel, and 
find the mass of the water in grams. Determine the mass 
of one cubic centimetre by dividing this number by loo. 
It will be found that the mass of one cubic centimetre is 
one gram very nearly. It would be exactly if the water 
were at a certain temperature. 

A convenient way to add or take away small quantities 
of liquid is by means of a pipette, used as shown in Fig. 32. 

Counterpoise a pint measure or bottle with some sheet 
lead. Fill the bottle with water, and place iron weights in 
the opposite pan to balance it. Notice that the size of the 
iron is much less than the size of the pint of water. 



^1000 

#-900 

^100 
S-(00 



l^» 





Fig. 31. — Measuring jar, 
graduated in cubic centimetres. 



Fig. 32. — How a pipette is 
used. 



REASONS AND RESULTS. 

The Meaning of Density. — In an earlier lesson an explana- 
tion was given of the meaning of the word dense, and lead was 
mentioned as an example of a dense substance. You must now 
learn more exactly what the word dense, or density, means. 

If different solids are obtained, of the same size or volume, 
every boy knows that they will have different masses. Suppose, 



48 



ELEMENTARY PHYSICS AND CHEMISTRY. 



for instance, we determine the mass of a cubic centimetre of 
wood, lead, cork, and marble, one after the other. The lead 
will be found to have the greatest mass, or be heaviest, the 
marble will come next, and then will follow the wood and 
cork in order. We thus find that equal volumes of these 
different solids have different masses. 

By filling two bottles of the same size with different liquids, 
it can also be shown that equal volumes of different liquids 
have different masses. And when different gases are compared 
in the same way, equal volumes of these, too, are found to 
have different masses. 






Fig. 33. — A bottle of water is heavier 
than a bottle of spirit of the same size. 



Fig. 34. — .4 pint of water has a mass 
of a pound and a quarter. Notice the 
piece of lead under the ij lbs. to 
counterpoise the empty bottle. 



Or, if we compare the size of a pint of -water with that of one 
and a quarter pounds of iron, we find that, though as shown by 
weighing, the masses of these things are equal, yet their sizes 
are very unequal. Hence we may say that equal masses of iron 
and water have very different sizes. 

Two facts, which should never be forgotten, are taught by 
experiments of this kind. They are : 

1. Lumps of different substances of the same size or volume 
may have unequal masses. 

2. Lumps of different substances which have equal masses 
may have very different sizes or volumes. 

It is usual to speak of these facts by saying that things have 
different densities. Referring again to an example we have 



DENSITY. 49 

already used, a pound of feathers or cotton-wool has exactly the 
same mass as a pound of lead, but, as you know, both the 
feathers and cotton-wool take up much more room, or have a 
larger volume, than the piece of lead (Fig. 19). The matter in 
the lead must be packed more closely than in the cotton-wool, 
which accounts for it taking up less room. The shortest way of 
saying all this, and the way in which you must express it for 
the future, is to say that lead is denser than either cotton- 
wool or feathers. 

If the size of a thing whose mass is great is very little, then it 
is called a dense thing, or is said to have a high density. If, on 
the other hand, the size of a thing is \-ery great and its mass 
ver)' small, it is said to have a low density. Lead is a sub- 
stance with a high density, because, as you know, a small piece 
of it has a large mass. Pith and cork, on the contrary, have 
a low density, because a very large lump of either of them 
has a small mass. 

How Densities are compared. — It is easy to compare densities 
when lumps of exactly the same size are used. Since the 
volumes are the same, it is quite clear that the thing with the 
greatest mass is the densest, and that which has the smallest 
mass is the least dense, so that we can compare the densities 
of these things by their masses. If we arrange them in order, 
putting the heaviest at the top, thus, 

lead 
marble 
wood 
cork 

we can say that lead is denser than marble, marble than wood, 
and so on. Moreover, the densities of these things having the 
same size are in the same proportion as their masses. 

Standard of Density. — But to compare densities it is better 
to have a standard, just as we have a standard of length, the 
yard, v/ith which to compare other lengths ; or a standard 
of size with which to compare other sizes. The density of 
water at a certain fixed temperature is taken as the standard. 
[This temperature is called four degrees centigrade, and written 
I. D 



so ELEMENTARY PHYSICS AND CHEMISTRY. 

4° C, which you will understand after you have studied the 
thermometer.] 

The mass of one cubic centimetre of water at 4° C. is one 
gram, and its density is taken as the standard of density, and 
is called i. Similarly, a substance, the mass of a cubic 
centimetre of which is two grams, would be said to have a 
density of 2, for it must contain twice as much matter as 
water does, packed into one cubic centimetre. The mass of 
a cubic centimetre of quicksilver is 13! (i3'6) grams, i.e. it 
contains I3f times as much matter in one cubic centimetre 
as there is in one cubic centimetre of water. Its density is 
therefore 13I or I3"6. 

To BE Remembered. 

Equal volumes of different substances may have different masses. 

Equal masses of different substances may have different volumes. 

Density is shown by the proportion of mass to volume. 

The standard density is the density of water at a temperature of 
4 degrees on the centigrade thermometer. 

The mass of a cubic centimetre of water at a temperature of 
4° C. is I gram, and the mass in grams of a cubic centimetre of any 
substance at this temperature is the density of the substance. 

Exercise XII. 

1. How would you show that equal volumes of different substances 
may have different masses? 

2. If you had equal masses of iron and water, which would have the 
larger size ? What conclusion would you draw from the difference ? 

3. What is meant by the density of a substance ? Name several 
things with a high density and several things with a low density. 

4. The density of what substance is taken as the standard? How 
would you proceed to find the mass of a cubic centimetre of water? 
What result would you expect to obtain ? 



DENSITY. 51 

LESSON XIII. 

DENSITY— Continued. 

PRACTICAL WORK. 

Things required.— Small bottle, or medicine phial, with glass 
stopper having a groove, made by means of a file along the part 
which fits into the bottle ; also a bottle with a file mark across it 
near the top. Balance and a box of weights. Small nails for 
counterpoising. 
What to do. 

Clean and dry the bottle having a mark across it. 
Counterpoise the bottle with a pill box containing very 
small nails or lead foil. Now fill the bottle with water 
up to the mark,- and find, by weighing, the mass of the 
water. 

Empty out the water and fill up to the mark with the 
liquid whose density is required, such as methylated spirit 
or milk. As before, find by weighing the mass of spirit 
or milk in the bottle. The masses of equal volumes of the 
two liquids are thus obtained. 

Consider the use of the grooved stopper in the second 
bottle, and use the bottle to determine the masses of equal 
volumes of two different liquids. 

REASONS AND RESULTS. 

How the Density of a Thing is measured.— This becomes 
very easy when water is taken as a standard. All we want to 
do to know the density of any substance is to ascertain the mass 
of a cubic centimetre of the substance. This number tells us, 
since the mass of a cubic centimetre of water is i gram, how 
many times heavier or lighter the substance is than the 
standard, water ; and this, as you know, is the density of the 
substance. 



52 



ELEMENTARY PHYSICS AND CHEMISTRY. 



We can now think of density in two ways. We can either 
regard it as 

(i) The number of times a substance is heavier or lighter 

than water, or, as 
(2) The mass of a cubic centimetre of the substance. 

Let us go one step further. What is true of one centimetre of 
each of the things we are considering, namely, the standard water 
and the substance whose density is required, will also be true of 
two centimetres, or any other number of centimetres. So long 
as we keep the sizes or volumes the same, then, we can compare 
the densities in just the same way, for the number of times the 
substance is heavier or lighter than water can be determined at 
once by a simple division sum. But we need not measure the 
volume in cubic centimetres. ^ Cubic inches or cubic feet would 
do just as well. All we want to be quite sure of is that their 
volumes are the same. 

Experimental Determination of Density of Liquids. — Since 
we only have to be quite sure that the volume of the water and 

the other substance are exactly the 
same in order to compare their 
densities at once, it is a very easy 
matter to find the density of a 
liquid. All we have to do is to 
take a bottle and scratch a mark 
on it, and fill it up to this mark 
with the various liquids, and we 
shall be quite sure this gives us the 
same volume of each of the liquids. 
Or, we can completely fill a bottle 
with one liquid after another, and 
so obtain equal volumes of them. 
A convenient way to do this is to use a bottle like the one shown 
in Fig. 35, having a stopper with a groove cut on it, or a hole 
bored through it. When such a bottle is filled with a liquid, 
and the stopper is put in, some of the liquid passes up through 




Fig. 35. — A bottle with a groove 
in the stopper, for determining re- 
lative density. 



1 At this stage it is assumed that the substance is at 4° C, but tins has not 
been insisted on too much lest the reader should get confused. 



DENSITY. 53 

the groove to make room for the stopper. A bottle of this 
kind may be named a density bottle. 

Suppose the mass of water in a density bottle was found to 
be 50 grams, and the mass of the same volume of methylated 
spirit was found to be 40 grams. Then these numbers show 
the relative densities of the two liquids, and as we take the 
density of water as the standard or unit, the density of the 
spirit is equal to 40 divided by 50. It is thus seen that 
the density of spirit is represented by the fraction f§ or |, 
which written as a decimal fraction is o'8. 

The density of many liquids is greater than that of water. 

Thus milk has a density represented by the number roj, or 

ifoo) so '^hat equal volumes of water and milk would have 

masses in the proportion of icx) to 103. In all cases, whether 

solids or liquids are used in the experiments, we can say 

^. . - , mass of substance 

Density of substance = ^ , , ^ . 

mass 01 equal volume or water 

To BE Remembered. 

Density may be considered as (l) the mass of a cubic centimetre 
of a substamce, or (2) the number of times a substance is heavier or 
lighter than an equal volume of water. 

Relative density is equal to the mass of a substance divided by the 
mass of an equal volume of water. 

To find the relative density of a liquid a density bottle is used, and 
the mass of liquid which fills it is divided by the mass of water which 
fills it. 

Exercise XIII. 

1. State clearly the two ways in which you have learnt density may 
be spoken of. 

2. If a cubic foot of any liquid has a mass ten times greater than 
that of a cubic foot of pure water, what would be its density? 

3. Draw a density bottle, and explain how it is used. 

4. The density of quicksilver is I3f ; what does this mean? 

5. Explain fiaily how you would determine the density of vinegar. 



54 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON XIV. 

DETERMINATION OF DENSITY. 

PRACTICAL WORK. 

Things Required. — U-tube mounted upon a strip of board. 
This U-tube can be made by bending a piece of glass tubing, 
or by connecting two pieces of tubing of equal bore with a 
piece of india-rubber. Quicksilver, milk, vinegar, and similar 
common liquids. 
What to do. 

Pour quicksilver into one of the branches of the U-tube 
until it reaches a horizontal line drawn on the board 
(Fig. 36). 

Now introduce water into one of the tubes, and notice 
that the mercury on which the water rests is pushed down ; 
afterwards introduce enough water into the other tube to 
bring the mercury back to its original level. By measuring 
you find the length of each column of water is the same. 
Repeat the experiment with different quantities of water. 

Remove the water and dry the tubes, and see that the 
mercury is up to the mark. Nearly fill one of the tubes 
with some liquid, such as methylated spirit, and balance 
it with water introduced into the other tube. Measure 
the lengths of the columns of liquid. 

REASONS AND RESULTS. 

Balancing Columns of Water. — A convenient way to balance 
liquids against one another, and so determine their relative 
densities, is by means of a glass tube bent in the form of a U. 

When we arrange a U-tube, as in Fig. 36, the mercury in the 
bend acts just like a pair of scales, and we are able to balance a 
column of water in one of the upright arms with a column of the 
same length in the other. We are then able to argue thus : the 



DETERMINATION OF DENSITY. 



55 



columns of water are the same size, or ha\e the same volume, 
and they balance one another, and consequently their masses 
must be the same ; and, finally, since their masses are equal 
and their volume the same, they 
must have the same density. 

Balancing Columns of Different 
Liquids. — But suppose we put 
water in one arm of the U-tube, 
and enough methylated spirit 
into the other to make the mer- 
cury stand at the same height 
in the two arms. 

Here we have a different state 
of affairs. The column of spirit 
which balances the column of 
water will be the longer, hence 
its size or volume is greater, 
since the tubes are the same 
width. But because they balance, 
their masses must be the same. 
Which is the denser? Evidently 
the water is. But how much 
denser? We can, since the 
masses are equal, easily calculate 
this. We mav sav 




Fig. 36. — An arrangement for balanc- 
ing columns of liquid. Mercury is in 
the bend of the tube, up to the line on 
the upright board. 



Density of spirit: 



length of water column 
length of spirit column' 



This is a ver\' good way to compare the densities of liquids. 
How the Density of a Solid is found. — The rule in the 
case of a solid is just the same as with a liquid ; but the 
plan of getting the mass of a volume of water exactly equal 
to the vc'ume of the solid depends upon several things, which 
you have yet to learn about, as to the way in which solids float 
or sink in water. It will be wisest to first study this subject, 
and then to try and learn how to measure the density of any 
solid. This we shall try to do in the next lesson. 



56 ELEMENTARY PHYSICS AND CHEMISTRY. 

To BE Remembered. 

When columns of liquid balance one another, the denser the 
liquid the shorter is the column. If spirit and water are used 

^ . ,- • • length of water column 

Density of spirit = , — ^-^ ;= r-^ ; . 

length of spirit column 

The density of any other liquid can be determined by balancing a 
column of it against a column of water. 

Exercise XIV. 

1. Two glass tubes of equal width are connected by india-rubber 
tubing and arranged in the shape of a U. The bend is filled with 
quicksilver. If water is poured into one tube, and spirits of wine 
into the other, until they exactly balance one another, which liquid 
will stand higher, and why? 

2. Water is poured into one of the tubes in the apparatus described 
in the last question until it half fills the tube. How much water 
must be poured into the other tube to just balance it ? Why ? 

3. Which liquid has the greater density, water or milk ? Describe 
a method by which you would find out the density of milk. 

4. In an experiment with a U-tube, it was found that a column 
of olive oil 10 inches in length balanced a column of water 9 inches 
long. What is the relative density of olive oil? 



LESSON XV. 

THINGS WHICH SINK IN WATER. 
PRACTICAL WORK. 

Things requirea. — A fish-globe, such as are sold to keep gold 
fish in, or a large clear glass finger-bowl ; pieces of lead, iron, 
oak, pine, cork. Glass cylinder divided into cubic centimetres. 
Irregular solid, such as a glass stopper or a pebble. Mercury 
in a saucer or tumbler. 
What to do. 

Fill the fish-globe or finger-bowl with water, and care- 
fully place lumps of different things, e.g. pieces of lead, 



THINGS WHICH SINK IN WATER. 



57 



iron, oak, pine, and cork, one after another, into the water. 
Obser\'e that (i) some sink and others float, (2) of those 
which float some sink further into the water than others. 
Take the objects which sink in water and place them in 
mercury. Notice that they float. 

Partly fill a glass cylinder, divided into cubic centimetres, 
and record the level of the water therein. Drop in one of 
the cubic centimetre solids which sinks, and again read 
the level of the water ; put the others in in order, recording 
the level of the water after each such addition. It will 
be found that the level increases by i cubic centimetre 
division in each case. 

Take any solid, such as a glass stopper or a marble, and 
drop it gently into water contained in the graduated glass 
cylinder. Read the level of the water before and after 
dropping the solid in ; the difference between these readings 
will give vou the volume of the solid in cubic centimetres. 



REASONS AND RESULTS. 

Some Things sink, others float in Water. — When you throw 
a stone into water what happens to it? It sinks to the bottom. 
But if you throw a piece 



of wood into water does it 
also sink ? No, it floats. 
By noticing what happens 
when different substances 
are put in water you can 
easily divide them into two 
classes. Those in onedivi- 
sion all sink, while those 
in the other all float. And, 




Fig. 37. — Some things sink, and others float, 
in water. 



of those that float, some sink further into the water than others. 

But you must not suppose that substances which sink in 
water will sink in every liquid. As a matter of fact, soHd iron, 
or even lead, will float upon mercury. 

Volume of Water displaced by Bodies placed into it. — If we 
put water into a narrow glass cylinder, and then add lumps 
of material of such a size and shape that they will go into 



58 



ELEMENTARY PHYSICS AND CHEMISTRY. 



the vessel easily, we can, by first making a mark on the cylinder 
at the level of the water and then dropping in the things one at 
a time, show that, no matter whether they sink or float, the water 
stands higher when the solids are in it than it did before. Or, 
as it is usually stated, the solids in every case displace a certain 
amount of water. How much water is thus displaced? Evi- 
dently the amount depends upon the volume of the part of 
the solid under water. 

How to determine the Volume of an Irregular Solid. — If a 
solid one cubic centimetre in size sinks in water it pushes 
aside one cubic centimetre of water to make room for itself 
If its size is two cubic centimetres, it makes two cubic centi- 
metres of water rise above the level the water had at first. 
Whatever the size of the solid, it must have room, and this 
room is obtained by displacing an amount of water of exactly 
the same size. 

This is a very useful fact to remember. For suppose you 
wish to find the volume of a stone having an irregular shape. 

It would be difficult to do this by 
measuring the stone, but the stone 
could be placed in a vessel of water 
and the rise of level produced by 
it noticed. The water displaced 
could then be poured into a cubic 
inch box or into a cubic centimetre 
box, and the number of cubic inches 
or cubic centimetres could be thus 
found. Or, we could get a glass 
measure having cubic inches or cubic centimetres marked upon 
it, and pour the displaced water into it. But the best plan of 
all is to use a vessel having cubic centimetres marked upon 
it. Water can be put in such a vessel up to a certain mark, 
and the number of cubic centimetres of water displaced by 
the solid can be seen at once by noticing the number of 
divisions between the levels of the water before and after the 
solid is put in. 

The Volume of Water displaced may be measured in Cubic 
Inches.— Though in every one of the experiments in our 
lessons on the displacement of water we have usually spoken 




Fig. 38. — The rise of level of the 
water when the stone is put in 
shows the volume of the stone. 



THINGS WHICH SINK IN WATER. 59 

of the volume of water displaced as being a certain number 
of cubic centimetres, there is no reason why, if we preferred 
it, we should not measure this and other volumes in cubic 
inches, cubic feet, or any other measure of volume. The 
principle is the same, and the choice of the unit of volume 
quite a matter of convenience. Cubic centimetres are generally 
used to measure such volumes as these, because of the simple 
relation which exists between the unit of volume and the 
unit of mass in the metric system. As we have learnt, the 
mass of a cubic centimetre of water at a certain fixed tempera- 
ture is exactly one gram. 

To BE Remembered. 

When an object sinks in a liquid the volume of liquid displaced by 
the object is equal to its own volume. 

To determine tlie volume of an irregular solid it is immersed in 
water, and the volume of water displaced is observed. 

Exercise XV. 

1. Pieces of iron, cork, wood, pith, and lead are thrown into a 
trough of water. How will the different substances behave? 

2. How would you find out die volume of water displaced by a 
solid which sinks? 

3. You are gjiven a large glass marble and told to find its volume 
without measuring or calculating. How would you do it? 

4. Does it make any difference whether the graduated glass vessel 
into which solids are put when we want to find their volumes by 
immersion in water is divided into cubic centimetres or cubic inches? 

5. The level of water in a graduated jar with cubic centimetre 
marks upon it is noted. A pebble is placed in the water, and it 
causes the level to rise 19 divisions. What is the volume of the 
pebble ? 



6o 



ELEMENTARY PHYSICS AND CHEMISTRY. 



LESSON XVI. 



THINGS WHICH FLOAT IN WATER. 



PRACTICAL WORK. 



Things required. — Rectangular rod of wood, i square cm. in 
section and about 1 5 cm. long, with lines around it i cm. apart. 
A small piece of the wood is gouged out of one end, and lead 
is put into the hole ; and the end is then made flat by filling 
in with wax. Graduated jar. A lactometer. Narrow test tube 
with mercury or shot in it. Balance and box of weights. 
What to do. 

Put some water in the graduated jar, and notice its level. 
Find the mass of the rectangular rod, and then place the 





Fig. 39. — The number of 
cubic centimetres in the part 
of the rod under water is 
equal to the number of cubic 
centimetres of the water dis- 
placed. 



Fig. 40. — The mass of the 
test-tube and contents is equal 
to the mass of water displaced. 



rod in the jar with the leaded end downwards. Notice how 
many cubic centimetres of the rod are immersed, and also 
how many cubic centimetres of water are displaced. Since 
the mass of i cub. cm. of water is i gram, the number of 
cubic centimetres of water displaced is also the mass in 
grams of the water displaced. This mass will be found 
equal to the mass of the whole rod. 

Fill the divided glass cylinder with water up to a certain 
mark. Notice the level of the water. 



THINGS WHICH FLOAT IN WATER. 6i 

Make a mark across a test-tube about two-thirds of the 
distance from the bottom of the test-tube. Float the test- 
tube in the water and put mercury or shot into it until the 
mark upon it is on a level with the surface of the water. 
Notice the number of cubic centimetres of water displaced 
when the test-tube is thus immersed. 

Then take out the test-tube, dry it, and determine its 
mass together with the mercury it contains. The total 
mass of the test-tube and contents will be found equal to the 
mass shown by the number of cubic centimetres of water 
displaced. Repeat the experiment with the test-tube im- 
mersed to a different mark. 

Float the test-tube and contents in spirits of wine and 
milk in succession. Notice that in the former case it sinks 
deeper than the mark, while in the other not so deep. 

Place the loaded test-tube or a lactometer (i) in milk, 
(2) in water, (3) in a mixture of milk and water. Observe 
the depth to which it sinks in each case. 

REASONS AND RESULTS. 

Water displaced by Solids which float. — You have learned that 
a solid which sinks in water or any liquid displaces a volume 
of liquid equal to its own volume. When a solid floats, the case 
is slightly different. Part of the solid is in water and part out of 
the water, and, of course, only the part immersed is pushing the 
water aside in order to make room for itself In the case of a 
floating object, therefore, the volume of liquid displaced is equal 
to the volume of the part of the solid below the surface. 

What decides the Depth at which an Object floats in Water? 
— When any object is floating in water, a certain volume of it is 
under water and a certain volume is above the surface. You 
know very well that the depth at which it floats depends upon 
its heaviness, or, in more exact words, upon its density. A rod 
of heavy wood sinks deeper in water than a rod of light wood of 
the same size. The water displaced by the heavy wood has 
therefore a greater volume, and consequently a greater mass, 
than that displaced by the light wood. But there is one 
important fact which applies to both cases, and should be kept 



62 



ELEMENTARY PHYSICS AND CHEMISTRY. 



/r\ 



well in mind. It is that the mass of the water displaced by the 
immersed part of a floating object is equal to the whole mass 
of the object. If therefore you are asked how far does an object 
which floats sink into water, the answer is — it goes on sinking 
until it has displaced an amount of water whose mass is equal to 
that of the whole mass of the floating object. 

How far will an Object sink in other Liquids in which it floats? 
— Since the depth at which an object floats in water is decided 
by the rule we have just learnt, namely, that it goes on sinking 
until the mass of the water displaced by the 
immersed part of it is equal to the mass of 
the object itself, we have a ready way of 
deciding whether an object will sink further 
in another liquid or not so far. If the liquid 
into which it is put is less dense than water, 
like spirits of wine, it is clear that to make 
up a given mass we shall want more of the 
liquid. Consequently, to make up a mass 
equal to the mass of the floating body, the 
object will have to sink further into the spirit 
than into the water. If, on the other hand, 
the object is placed in a liquid such as 
mercury, which is denser than water, it will 
not sink so far, because it will not take so 
much of this denser liquid to have a mass 
equal to that of the floating body. 

The Lactometer. — This fact is made use of 
in the construction of the simple instrument 
called a lactometer (Fig. 41), used to test 
the density of milk. When placed in pure 
milk a lactometer should float with the mark 
P (Fig. 41) on a level with the surface of 
the liquid. In a mixture of milk and water 
the lactometer floats with some other division 
level with the surface of the liquid. Thus, 
in milk 10 per cent, below the average density, the 10 above 
the mark P is level with the surface. 

An experienced observer is able, therefore, from the readings 
of a lactometer to tell whether a sample of milk has a correct 




Fig. 41. — A lacto- 
meter, for testing the 
quality of milk. It 
sinks to the mark P 
when put in pure-milk. 



THINGS WHICH FLOAT IN WATER. 63 

density, or whether it is heavier or lighter than it should be. 
At the same time it must be clearly understood that it is not 
possible to decide at once from the reading of a lactometer 
whether a sample of milk has been adulterated or not. There 
are other considerations to be taken into account. 

To BE Remembered. 

When an object floats in a liquid, the volume of liquid displaced is 
equal to the volume of the immersed portion of the object. 

The mass of the water displaced by a floating object is eijual to 
the whole mass of the object. 

An object which floats in water sinks deeper into a liquid which 
is less dense than water, and not so deep into one which is denser 
than water. 

A lactometer is an instrument for testing the proportion of watar 
which may have been added to milk. 

Exercise XVI. 

1. What is the volume of water displaced by an object which floats 
in it? 

2. How far will a given object sink into water ? 

3. Will a lead pencil sink further into spirits of wine or into water 
when floated in these liquids ? Give reasons for your answei. 

4. WTiy does a piece of oak sink further into water than a piece of 
deal the same size ? 



04 



ELEMENTARY PHYSICS AND CHEMISTRY. 



LESSON XVII. 



PRINCIPLE OF ARCHIMEDES. 



PRACTICAL WORK. 



Things required. — Brick with string tied to it. Pail -of water. 
Metal cube or other heavy object. Spring balance. Tumbler. 
Balance with one pan having short suspension cords or chains 
and a hook soldered to the bottom. Box 
of weights. Graduated jar. Small tin 
canister. Small nails or shot. Methy- 
lated spirit or turpentine. 
What to do. 

Hold a brick by a string having 

one end tied round it. Keeping the 

„^ , .jr. string in your hand, lower the brick 

M{ ,'i'p into a pail of water, and notice that 

the brick seems to become lighter 

when it is immersed in the water. 

Suspend a metal cube, or any 
other fairly heavy object, from a 
spring balance, and notice the 
reading of the balance. This indi- 
cates the weight of the object in air. 
Immerse the cube in water, as in 
Fig. 42, and again notice the reading 
of the balance. It is less than 
before, and the loss of weight shows 
the buoyant power of the water. 
Find the volume of the cube, or other object used in 
the last experiment, by noticing the volume of the water 
it displaces in the graduated jar. 




Fk;. 42. — The block weighs 
less when immersed in water 
than when suspended in air. 



PRINCIPLE OF ARCHIMEDES. 



65 



Hang the object from one pan of the balance, as shown 
in Fig. 43, and determine its mass in grams. Now bring a 
vessel of water under the pan so that the object is immersed 
in it, as in Fig. 44. The pan rises, indicating a loss of 
weight. Put gram weights in the pan until the balance sets 
horizontally as before. You thus find the apparent loss of 
mass due to the buoyancy of the water. Notice that the 
number giving this loss in grams is the same as that 
giving the volume of water in cubic centimetres dis- 
placed by the object. 




Fio. 43. — Weighing an object in air. Fig. 44. — The same object weighed in 

water. Notice that weights are in the 
short pan to make up for the buoyancy of 
the water. 

It time permits, repeat the experiment with another 
object, and find again that the number giving its volume 
in cubic centimetres is the same as that showing the loss 
of weight (measured as before) when immersed in water. 

Procure a small tin canister about half the diameter of 
the graduated jar. Put some water into the jar. Notice 
the level Place the canister in the water and gradually 
put shot or small nails into it until it just sinks in the water 
when the cover is on. Pour the water displaced by the 
canister into a beaker counterpoised upon a balance ; then 
take out the canister, wipe it, and place it in the other pan 
of the balance. You will find that the mass of the canister 
and shot is practically the same as the mass of the water 
displaced. 



66 ELEMENTARY PHYSICS AND CHEMISTRY. 

Repeat the experiment, using another liquid, such as 
methylated spirit, or turpentine, instead of water. 



REASONS AND RESULTS. 

Buoyancy. — Most boys and girls have noticed when in a bath 
that if there is water enough, and they take hold of no support, 
the water buoys them up, or they experience a tendency to rise 
up through the water. In the case of things which float, such 
as a wooden rod or a lead pencil, you can easily see the results 
of this buoyancy which the water exerts, by pushing either the 
rod or pencil down into the water and then letting go, when the 
solid floats up through the water. Even in the case of bodies 
which sink, there is the same buoyancy on the part of the water, 
but it is not enough to float them. The effect which the water 
has upon such bodies can, however, be seen in the loss of weight 
which they experience if they are weighed by a spiing balance 
when hanging in water (Fig. 42). 

Loss of Weight of Things immersed in Water. — It is easy to 
prove by experiment that an object weighs less in water than 
out of it. If a cubic centimetre of lead, or any other heavy 
material, is hung from a spring balance and then suspended in 
water, it will be found to weigh the weight of one gram less in 
water than out. If two cubic centimetres are suspended from 
the balance, the loss of weight is the weight of two grams. 
In every case the loss of weight measured in this way is equal 
to the number of cubic centimetres of the solid immersed 
in the water. The loss is thus equal to the weight of the water 
displaced. This fact brings us to a highly important conclu- 
sion, known after its discoverer as the Priticiple of Archimedes. 

The Principle of Archimedes — When a Body is immersed in 
Water it loses Weight equal to the Weight of the Water dis- 
placed by it— If the body be immersed in any other hquid, 
then, the loss of weight is equal to the weight of an equal 
volume of that Hquid. It does not matter what substance a 
thing is made of ; the amount of loss of weight depends upon 
the volume of the part immersed and not upon the material. 

We can now understand many interesting facts. For in- 
stance, a ship made of iron, and containing all kinds of heavy 



PRINCIPLE OF ARCHIMEDES. 67 

things, is able to float in water although the material of which 
it is made is denser than water. This is because the ship 
and all its contents only weigh the same as the volume of 
the water displaced by the immersed part of the hull. Or, 
the ship as a whole weighs less than a quantity of water the 
same size as the ship would weigh. 

Now, too, we can see why some solids float and some sink. 
When an object weighs more than an equal volume of water 
it sinks. When an object weighs less than an equal volume 
of water it floats. When an object weighs the same as an 
equal volume of water it remains suspended in the water. 

A balloon rises in the air because the gas in the balloon, 
together with the bag and tackle, weighs less than an equal 
volume of air. If the balloon were free to ascend it would 
rise to a height where its weight would be equal to the weight 
of an equal volume of air. 



To BE Remembered. 

Buoyancy is the support given by liquids to objects immersed in 
them. 

Objects immersed in water appear lighter than when they are out 
of water. 

The Principle of Archimedes states that when an object is immersed 
ill a liquid it experiences a loss of weight equal to the weight of the 
liquid displaced by it. 

Iron ships float because they are lighter bulk for bulk than an equal 
volume of water. 

The weight of the mass of water displaced by the part of a ship 
in water is equal to the weight of the whole mass of the ship. 



Exercise XVII. 

1. Why do things lose weight in water? How would you measure 
this loss of weight ? 

2. What is meant by the Principle of Archimedes? 

3. A piece of iron sinks in water while a cork floats. What is the 
reason of this? 

4. What do you understand by buoyancy? 

5. Why will an iron ship float in water? 



68 



ELEMENTARY PHYSICS AND CHEMISTRY. 



6. An object having a volume of 27 cubic centimetres has a mass 
of 124 grams in air. What is its weight in water? 

7. The mass of an object appears to be 19 grams less in water 
than in air. What is the volume of the object? 



LESSON XVIII. 

DETERMINATION OF THE DENSITY OF A SOLID. 

PRACTICAL WORK. 

Things required. — Balance and box of weights. Pebbles, 
and other solids suitable for determination of densities. Beaker 
of water. Fine thread 
What to do. 

Attach the solid the density of which you are going to 
determine to one side of the balance, as shown in 




Fig. 45. — How to find the weight of an object suspended in water. 



Fig. 45. By weighing, find its mass in air. Then 
immerse the solid in water placed in a beaker standing 
upon a small platform ////, as shown in Fig. 45. Find 



DETERMINATION OF THE DENSITY OF A SOLID. 69 

its weight in water, and, by subtracting this number from 
its weight in air, determine the loss in weight of the 
sohd when suspended in water. 

Another plan of determining the weight of an object in 
water was explained in the last lesson (Fig. 44). 

This loss of weight equals the weight of a volume of 
water equal to the volume of the solid. We can therefore 
\vrite : 

Density of solid^^^^^^ ofjhe solid in air 
Its loss of weight in water 



REASONS AND RESULTS. 

How the Relative Density of a Solid is determined.— We left 
this problem over from a previous lesson, in which we learnt 
how to determine the density of a liquid compared with water. 
Until you had studied what you have now learnt to call the 
Principle of Archimedes, it was not possible to understand the 
steps by which the relative density of a solid is obtained. But 
now that you have found out that when a body is immersed 
in water it loses weight equal to the weight of the water 
displaced by it, you are in possession of all the information 
necessary for determining the density of a solid compared with 
water. 

All we want to know is : 

1. The mass of the object, which we can determine by 

weighing it in air. 

2. The mass of an equal volume of water. 

And the Principle of Archimedes enables us to do this in 
the following manner : 

We hang the object, by means of a fine thread, from one side 
of the beam of a balance in such a way that it is completely 
immersed in water. Then by weighing we observe that its 
mass appears less than when hanging in air. This is because it 
loses weight in the water. The buoyancy of the water acting 
upwards overcomes part of the pull of the earth downwards. 
The difference in the mass of the object in air and its apparent 
mass when immersed in water gives us the mass of a volume 
of water equal to the volume of the object. From these 



70 ELEMENTARY PHYSICS AND CHEMISTRY. 

numbers we can at once calculate the density of the solid 
compared with water as a standard : 

Mass of the obiect in air 



Density of the solid = 



Mass of an equal volume of water 



But the weight of an object at any particular place depends 
directly upon the mass, consequently we can substitute the 
word weight for mass in this case, and can therefore write as 
follows : 

Weight of the object in air 



Density of the solid = 



Weight of an equal volume of water 



Another way to find the Mass of an Equal Volume of 
Water. — To find the mass of an equal volume of water, the 
object could be placed in a graduated jar and the amount 
of water displaced could be taken out and its mass determined 
by weighing. Or, if the number of cubic centimetres of water 
displaced is observed, the same number tells us the mass of 
the displaced water in grams. 

Example. — A piece of lead was found to have a mass of 
loo grams in air, and when suspended in water its mass 
appeared to be 90 grams. What is its density compared with 
water ? 

What must we do with these numbers to find out the 

density of the lead compared with water ? We want to 

know two things, you remember — first, the weight of the 

object in air. We know the mass by weighing, and the weight 

is directly proportional to this. Secondly, we want to know 

the loss of weight in water, as this gives us the weight of 

an equal volume of water. We get the loss of weight by 

subtraction, thus : 

T c ■ u^ The weight of") f The weisfht, or its 

Loss of weight = ^, ij^-^-l ^ ■ 

*' the lead m air J (apparent mass, in water 

= weight of 100 grams -weight of 90 grams 
= weight of 10 grams. 

.'. Density of the lead = — = 10. 
^ 10 

Since the density of this piece of lead is 10, we know that 
one cubic centimetre of it will have a weight equal to that 



DETERMINATION OF THE DENSITY OF A SOLID. 71 

of 10 grams. What is the volume of the piece of lead used 
in the example ? Evidently, since its weight is equal to that 
of 100 grams, its volume must be ten cubic centimetres. 

To BE Remembered. 

To determine the density of a solid, we determine (i) its mass 

in air ; (2) its apparent mass in water. From these numbers we can 

find the loss of weight which the solid experiences in water, and can 

say : -r^ ■ ^ ,• 1 Weight of solid in air 

■' Density of solid = :f ^ 7—. — -. 

^ Loss of weight in water 

Exercise XVIII. 

1. Describe fully, with a drawing, what weighings you would per- 
form to determine the density of a solid. 

2. Why does the mass of a solid weighed in water appear to be 
less than in air? 

3. A solid was weighed in air and found by a balance to have 
a mass of 120 grams.- When suspended in water and again weighed 
its mass seemed to be 100 grams. What is its density? 

4. How does the Principle of Archimedes assist in the determination 
of the density of a solid? 



LESSON XIX. 

THE AIR AROUND US. 

PRACTICAL WORK. 

Things required. — Glass trough full of water. Bottle. Flask 
or bottle fitted with funnel and tube, 
as in Fig. 48. Balance. Weights. 
Two 8 oz. flasks, one fitted with tubing 
and clip, as in Fig. 49. 

What to do. 

Tr)' to force an empty bottle, 
held upright with its mouth down- „ ^ xk • • ,v, 

' o Fig 46. — The air in the 

wards, into a vessel of water bottle cannot escape, and is 
,„. ^. ,,^ compressed as the bottle is 

(Fig. 46). WTien you leave go, pushed down into the water. 




72 



ELEMENTARY PHYSICS AND CHEMISTRY. 




Fig. 47. — As the water goes into the 
bottle, air bubbles out. 



the bottle jumps up again. There is something in it which 

acts like a spring. 

Tilt an empty bottle, held mouth downwards, in a 

trough of water, and notice 
the bubbles of air which pass 
up as the water enters the 
bottle (Fig. 47). 

Take a funnel with a narrow 
tube, and fit it firmly into a 
bottle by means of an india- 
rubber stopper with two holes 
in it. Through the second 

hole pass a short piece of glass tubing bent at right angles 

(Fig. 48). 

Place a finger over the open 

end of the tube, pour water into 

the funnel, and notice that, so 

long as you keep your finger 

upon the end of the glass tube, 

the water is prevented from 

getting into the bottle by some- 

FiG. 48. — The bottle only con- 
tains air, but the water will not 
run in until the finger is taken 
from the tube, and then the air 
can be felt coming out. 

thing — air — already there (Fig. 48). 
Take your finger away. The water 
now runs into the bottle, and air 
escapes from the tube. The escap- 
ing air may be felt, or its effect 
upon a lighted match may be seen. 
The following experiment needs 
to be carefully done with a good 
balance in order to be successful. 
Obtain two large flasks. Fit one 
with a closely-fitting india-mbber 
stopper, having a hole in it through 
which a short piece of glass tubing passes. Upon the 





Fig. 49. — When air is sucked 
out of the bottle, the bottle 
weighs less than before. 



THE AIR AROUND US. 



73 



india-rubber a clip is fastened (Fig. 49). Hang the flasks 
over the two pans of the balance, the fitted one having 
the stopper and tubing with it, and counterpoise them 
(Fig. 50). 




Fig. 50 — Cuunterpjibed flasks When air i-, sucked out of one flask, 
this flask becomes hghter than the other. 



Now insert a short glass mouthpiece in the india-rubber, 
open the clip, and suck air out of the stoppered flask, 
without touching the flask. Fasten the clip while you are 
sucking out the air. Take out the mouthpiece, and you 
will find that the flasks no longer counterpoise, the one 
from which air has been withdrawn being lighter than 
befoi-e. Admit air by opening the clip, and it will be 
found that the flasks again counterpoise one another. 



REASONS AND RESULTS. 

There is Air all round us. — Though we can neither see, smell, 
hear, nor taste it, there is air all round us wherever we go. We 
can feel it when it is blown against us in a wind, and see the 
results of its motion when it moves trees or loose objects on 
the ground. It drives windmills and blows sailing ships across 
the seas ; at times its force is so great that it blows down great 



74 ELEMENTARY PHYSICS AND CHEMISTRY. 

houses and produces mighty billows upon the ocean. When 
these things happen we become quite sure that there is air. 
And even on the calmest day the air can be felt by swinging an 
open hand to and fro, or by using a fan. 

Empty Vessels contain Air. — When a boy has used all the 
ginger beer or lemonade out of a bottle, he says the bottle is 
empty. This, however, is not exactly true. What is usually 
called an empty bottle is really a bottle of air. If the bottle 
is dipped under water with the mouth downwards and then 
tilted, the air will be seen bubbling out of it to make room for 
the water which runs in. Or, if water is allowed to run into 
it through a funnel passing through the cork, the air can be 
felt as it escapes through a hole in the cork. There can be 
no doubt, then, that the bottle contains air even when it looks 
empty, and the same is true for other so-called empty vessels. 

Air has Mass. — As air really exists and can be felt it must 
have mass, though the mass of a small quantity, such as a 
bottle of air, is very slight. We sometimes say that things are 
as light as air, but there are gases which are lighter still. The 
gas we burn in our houses, for instance, is lighter than the same 
volume of air. Compared with water, however, air is very light. 
A cubic foot of water has a mass equal to looo ounces, but 
a cubic foot of air, at the ordinary temperature and pressure, 
only has a mass of a little more than an ounce. Water is, in 
fact, about eight hundred times heavier than an equal bulk 
of air. 

To find the mass of the air in a pint bottle, the bottle 
must first be weighed full of air and then with the air sucked 
out by means of an air-pump. The difference between the 
two weighings shows the mass of a pint of air. 



To BE Remembered. 

Air surrounds us ; it can be felt when winds are blowing or by 
waving a hand through it. 

The bubbles which rise when an empty bottle is placed in water 
consist of air escaping from the bottle. 

The mass of air can be found by weighing a tightly stoppered 
bottle first full of air and then with the air sucked out. 



THE AIR AROUND US. 75 

Exercise XIX. 

1. What reasons have we for saying there is air all around us? 

2. Name some of the results caused by the movements of the air 
round us. 

3. How would you show that a so-called empty bottle really con- 
tains air ? Give a drawing. 

4. In what way can air be shown to have mass ? 



LESSON XX. 

THE PRESSURE OF THE AIR. 

PRACTICAL WORK. 

Things required. — Narrow glass tube or pipette. Leathern 
sucker. Flask fitted with tube as in Fig. 51 (the stoppered 
flask used in the experiment to determine the mass of air 
will do). Penny squirt or glass syringe. Cylinder or tumbler 
with ground glass edge. Piece of card large enough to cover 
mouth of cylinder or tumbler. Bellows. 
What to do. 

Dip a long tube— a pipette will do — into water. Place 
your finger over the top and lift the tube out of the water. 
Notice that the water does not run out of the tube although 
the bottom is open (Fig. 32). 

Moisten a leathern sucker, press it upon a flat stone, and 
notice that it can only be pulled off with difficulty, owing 
to the atmosphere pressing upon its upper surface. 

Fit a one-holed stopper into a flask of water. Push a 
piece of glass tubing through the stopper. Try ti^ suck 
up the water (Fig. 51). You cannot, unless you loosen the 
stopper so as to let the pressure of the air force the water 
up the tube. 

Dip the open end of a glass syringe or squirt into a 



76 



ELEMENTARY PHYSICS AND CHEMISTRY. 



tumbler of water (Fig. 52) ; pull up the piston, observe that 
the water follows it, owing to the pressure of the atmosphere 

upon the surface of the 



water in the tumbler. 

Take a tumbler or 
cylinder with ground 
edges and completely 
fill it with water. Place 
a piece of card-or stout 
writing paper across 
the top and invert 
the vessel. If the 
air has been carefully 
kept from entering the 
out (Fig. 53). Think 




Fig. 51. —The water in the flask cannot be 
sucked out while the cork is tight. 



tumbler, the water does not run 
what keeps the paper in its place. 

Procure a pair of bellows. Notice that the valve at the 
bottom only opens inwards. Open the bellows, and 
observe that the valve is pushed up a 
little as the air enters (Fig. 56). Close 
the bellows ; the valve is pushed down ; 
and, as the air cannot escape any other 
way, it is forced through the nozzle 
(Fig. 57). 

Tie a piece of thin india-rubber, such 
as is used in toy air-balls, over the 
mouth of a funnel. Suck air from the 
flmnel, and notice that the india-rubber 
is forced inwards by the pressure of the 
outside air. Place your finger over the 
open end of the funnel while the india- 
rubber is in this condition, and turn the funnel in differ- 
ent directions. Notice that the india-rubber undergoes 
no change in shape, thus showing that the air pressure 
outside is the same in different directions (Fig. 54). 




Fig. 52. — The pres- 
sure of the air forces 
water into the squirt 
when the piston is 
pulled up. 



THE PRESSURE OF THE AIR. 



77 





Fig. 53. — The paper does not fall off 
though the glass is full of water. 



REASONS AND RESULTS. 

Air exerts Pressure. — Even'thing which has weight can exert 
pressure. The pressure depends first of all upon what we have 

learned to call the density of a 
thing. For instance, if you 
carry a piece of iron upon 
your shoulder you arc pressed 
down more than by a piece of 
wood of the same size. But 
the pressure also depends, of 
course, upon the amount of 
material you are bearing. 
Thus, a sack of wool borne 
upon your head would exert 
more pressure than an iron 
nail. You will be able to 
understand, then, that though 
the air is so light 'compared with other 
substances, a large quantity of it would 
be ver\' heavy and would exert a ver}' 
great pressure. 

Now, the air above us extends up- 
wards from the surface of the earth for 
many miles ; and in consequence of 
this it presses very heavily upon every- 
thing. You will see in the next chapter 
how this pressure is measured, but 
there are many simple ways which 
show that it is real. 

The reason why a leathern sucker 
is difficult to pull off an object upon 
which it has been placed is that the 
air is pressing upon the outside of the 
sucker but not upon the inside (Fig. 55). 
When a liquid is drunk through a 
tube, the vessel containing the liquid mtist be open to the 
air or else it cannot be obtained. You may see that this is 
so by examining a baby's feeding bottle. If the stopper of 




Fig. 54. — The funnel at A 
has a sheet of india-rubber 
tied over the top. When ,iir 
is sucked out of the funnel the 
india-rubber curves inwards 
as at B, owing to the pressure 
of the air outside. 



78 



ELEMENTARY PHYSICS AND CHEMISTRY. 



the bottle is screwed in tightly, and there is no open hole in 

it, the baby cannot get his food, however hard he sucks. 
Air presses in all Directions. — The pressure of air is not only 

downwards, but upwards and sideways ; in fact, in all directions. 
If the pressure were only exerted 
downwards, then a sucker could be 
pulled off an object on which it is fixed 
by turning the object upside down or 
sideways. But you know that you 
cannot pull the sucker off any easier 
whatever way you turn it. 

The upward pressure of the air is 
shown by means of bellows. As the 
top board is lifted up, the air forces 
up the valve at the bottom and enters 
the bellows (Fig. 56). If there were 
no upward pressure, this of course 
could not happen. 
Why we do not feel the Weight of the Air above us. — Though 

our bodies are pressed upon by the whole weight of the air 

above us, we do not feel 




Fig. 55 — The sucker can- 
not be pulled off easily because 
the air is pressing on the top 
of it, but not on the lower 
side. 



The 
up a 




it. Why is this ? 
lungs, which fill 
large part of our chest 
space, are filled out with 
air, and this air is in free 
communication with the 
atmosphere through our 
throat and mouth. The 
result is that the air in 
the lungs presses them 
outwards from the in- 
side just as much as the 
atmosphere presses 
them inwards from the outside, and so we feel no incon- 
venience. It is just as if two equally strong boys are pulling 
as hard as they can from opposite sides of a door. Though 
they are both exerting all their strength, the door does not 
move. 



Figs. 56 and 57. 

When the bellows are being opened the valve 
rises and lets in air. 

When the bellows are being closed the valve is 
pushed down, and air is forced out of the nozzle 
or spout. 



±1111. X i\.ii,oo>j 1X11, \ur 1 iic^ ^\ii\.. 7y 

To BE Remembered. 

The pressure of air is due to its weight, and is shown by the use of a 
sucker as well as in other ways. 

When air is removed by suction from the inside of a tube dipping 
into a liquid, the pressure of the air outside forces the liquid up the 
lube. 

The reason why the pressure of air is not felt is that it is equal 
in all directions around us as well as inside our bodies. 

Exercise XX. 

1. What is meant by saying that air exerts pressure? 

2. Why cannot a baby get his food from a feeding bottle, if the 
stopper contains no hole and is tightly screwed down ? 

3. Why is it so difficult to pull off a leathern sucker from a damp 
stone ? 

4. Explain the action of a pair of bellows. 

5. How does a squirt act? 

6. Would a squirt act if there were no air around it? Give reasons 
for your answer. 

LESSON XXI. 

BAROMETERS. 

PRACTICAL WORK. 

Things required.— A barometer tube about 36 inches long. 
Piece of glass tubing about 6 inches long, and the same width 
as the barometer tube. Thick india-rubber tubing to connect 
barometer tube and short tube. Board having two linesj 28 
inches apart, drawn upon it, and a strip of paper divided into 
tenths of inches, gummed to the top, as shown in Fig. 58. 
Mercury. Cup to hold mercury. 
What to do. 

Tie a short piece of thick india-rubber tubing upon the 
open end of a barometer tube. Tie the free end of the 
tubing to a glass tube about six inches long, open at both 
ends. Rest the barometer tube with its closed end down- 
wards, and pour mercury into it (being careful to remove 
all air bubbles) until the liquid reaches the short tube. 
Then fix the arrangement upright as in Fig. 58. 



8o 



ELEMENTARY PHYSICS AND CHEMISTRY. 



The air pressing upon the surface of the mercury in the 
short open arm of the U-tube balances a long column of 
mercury in the closed arm. 




REASONS AND RESULTS. 



How the Pressure of the Air is measured. — 

It is very important that we should find a 
way of measuring how much the air presses 
upon things on the earth's surface. The 
instrument shown in Fig. 58 enables us to 
do this. The top of the long tube is sealed 
so that the air cannot press upon the mer- 
cury in it, but the small tube is open and 
the air can therefore press upon the mercury 
in it. 

Balancing Columns of Air and Mercury.— 
The instrument just mentioned is evidently 
very much like the U-tube used in Lesson XIV. 
Now look at Fig. 58, it is clear that there 
is a column of mercury supported by some 
means which is not at first plain. If this 
were not so, the mercury would sink to the 
same level in the long and the short tubes, 
for liquids always find their own level. If a 
hole were made in the closed end of the tube 
this would immediately happen. There should 
be no difficulty, from what has been already 
said, in understanding that the column of mer- 
cury is kept in its position by the downward 
force of the weight of the atmosphere pressing 
upon the surface of the mercury in the short 
open tube. The weight of the column of 
mercury, and the weight of a column of the 
atmosphere of the same size through, or of 
the same area, is exactly the same. Both the 
column of mercury and the column of air must be reckoned 
from the level of the mercury in the short stem of the barometer 
shown in Fig. 58— the mercury column to the top in the long 



Fig. 58.— The pres- 
sure of the air on the 
mercury in the small 
tube is able to keep 
up the column of mer- 
cury in the long tube. 



BAROIMETERS. 8i 

cube ; the air to its upper limit, which is at a great distance from 
the surface of the earth. 

Air Pressure shown by a Barometer. — The height must, m 
every case, be measured above the level of the mercury in the 
tube or cistern open to the atmosphere ; just as, in the case 
of the U-tube in Lesson XIV., the heights of the liquid columns 
had to be measured from a fixed line. In the arrangement 
shown in the accompanying illustration (Fig. 58), a line is drawn 
at a fixed point O, and the short tube is shifted up or down 
until the top of the mercury in it is on a level with the line. 

For an instrument of this kind to be accurate, great care has 
to be taken that no air enters the space at the top of the long 
tube. If air does enter, it will press upon the surface of the 
mercury in the long- tube, and the height of the mercury will 
be less than thirty inches. In such a case, instead of measuring 
the whole pressure of the atmosphere, what we should really 
be measuring would be the difference between the pressure 
of the whole atmosphere and. that of the air enclosed in the 
longer tube. In a -properly constructed barometer, therefore; 
there is nothing above the mercury in the longer tube except 
a little mercury vapour. 

An arrangement like that described constitutes a barometer 
A barometer is an instrument for measuring the pressure 
exerted by the atmosphere. 

A Common Form of Barometer. — You have probably seen a 
barometer, or weather-glass as it is called, of the kind shown in 
Fig. 59. In the inside of an instrument of this form there is a 
bent tube of exactly the same kind as has been described in this 
lesson. The only addition is a little weight which rests upon the 
mercury in the small tube, and therefore moves up and down as 
the mercury rises and falls. A cord attached to this float passes 
over a pulley connected with a hand which can turn like the 
hand of a clock. When, therefore, the mercury moves in the 
tube, the float moves up or down and the hand moves round. 
Marked upon the dial of the instrument are numbers corre- 
sponding to the number of inches in length of the long mercury 
column, measured from the level of the mercury in the small 
open tube. The length of the mercury column, or heio;ht of the 
barometer as it is termed, can thus be seen by noticing the 

I- F 



82 



ELEMENTARY PHYSICS AND CHEMISTRY. 



number on the dial to which the hand points. The way in 
which the instrument works can easily be understood by an 
examination of Fig. 59- 





Fig. 59.— Front and back of a barometer or weather-glass used to 
show changes in the pressure of the air, and therefore changes of 
weather. 

The short hand shown is useful for mdicating how much the 
height of the barometer has changed. It can be turned to 
point to any part of the dial. Suppose it is turned to point to 
the same number as the large hand on any day; then on 
looking again next day you could see how much the large hand 
of the barometer had moved from the place in which it was the 

day before. 

To BE Remembered 

A barometer is an instrument for measuring the pressure of the air. 

The principle of a barometer is that a column of mercury in a tube 
containing no air is balanced by the pressure ot the atmosphere outside 
the tube. 



BAROMETERS. 83 

The height of the mercury in a barometer is, on the average, 
30 inches at sea-level. The height changes slightly from day to day 
on account of alterations in the pressure of the atmosphere. 



Exercise XXI. 

1. How is the pressure of the air measured ? 

2. Describe fully and carefully how a barometer is made. 

3. Make a drawing of a barometer and name its parts. 

4. If a hole were made in the top of a barometer what would happen ? 

5. What is a barometer, and what is it used to measure ? 



LESSON XXII. 

WHY THE HEIGHT OF THE BAROMETER ALTERS. 
PRACTICAL WORK. 

Things required. — The barometers made in the last lesson. 
Another barometer tube, some mercury, and a small basin. 
What to do. 

Slip a piece of india-rubber tubing upon the open end 
of the barometer, and notice what happens when you 
blow vigorously down it. Suck air out of the tube, and 
observe the result. 

Fill a barometer tube with mercury ; place your thumb 
over the open end ; invert the tube ; place the open end 
in a cup of mercury, and take away your thumb. 

The mercury in the tube will be seen to fall, so as to 
leave a space of a few inches between it and the closed 
end. Measure the distance between the top of the 
mercury column and the level of the mercury in the 
cup. It will be found to be about thirty inches. If a 
tube less than thirty inches (76 centimetres) long is used, 
there is no space at the top. Tilt the barometer tube, 
and notice that by and by the mercury fills the tube. 



84 



ELEMENTARY PHYSICS AND CHEMISTRY. 




REASONS AND RESULTS. 
When the Height of the Mercury in a Barometer alters — 

If, for any cause, the pressure upon the surface of the mercury 
in the open tube increases, the mercury in the long tube will 
evidently rise. If, however, the pressure becomes less, the 

mercury column will get 
shorter. The effect of an 
increase of pressure can be 
shown by blowing into the 
small tube, and the effect of 
a decrease of pressure by 
sucking the air out of the 
small tube. 

When you blow down the 
short tube of the barometer, 
you are helping the atmos- 
phere to press upon the 
mercury ; and the atmosphere 
and your breath both together 
press more, and the mercury 
is pushed higher. When you 
suck, you are acting against 
the atmosphere, and there- 
fore reducing the pressure 
upon the mercury ; so that, 
both together, there is not so 
much pressing done as when 
the atmosphere acts alone ; 
this is why the mercury does 
not stand so high in the long 
tube. 

Another Form of Mercury 
Barometer — Instead of using 
a barometer of the U-tube 




Fig. 6o.— The tube is first iilled with 
mercury, and then placed with the open 
end in a cup of mercury. A colunin of 
mercury about 30 inches long remains in 
the tube. 



form, a straight tube sealed at one end may be filled with mer- 
cury, and inverted in a small cup of mercury, as shown in Fig. 60. 
A column of mercury will then be supported in the tube 
bv the pressure of the atmosphere. The distance between 



WHY THE HEIGHT OF THE BAROMETER ALTERS. 85 



the top of the column and the surface of the mercury m the 
cup will be about 30 inches, or 76 cm., when the tube is vertical, 
or in the position A in Fig. 61. If the tube is inclined to the 
position B, so that the closed 
end of it is less than this 
height above the mercury in 
the cup, the mercury fills the 
tube completely, showing that 
the space C above the mercury, 
when the tube was in the posi- 
tion A, did not contain air. 
It will be clear from this that 
if the tube were less than 30 
inches long, it would be en- 
tirely filled by the mercury. 
On an average, the atmosphere 
at the sea -level will balance a 
column ot 




>3olN. 




Fig. 61 — The tilted glass tube is full of 
mercury, but if it is placed upright in the 
position A the mercury will not fill it, and 
there will be nothing visible in the part C. 



mercury 
30 inches 
in length. 

No matter if the closed tube is 30 feet long, 
the top of the mercury column will only be 
about 30 inches above the level of the mer- 
cury' in the cistern. 

Weight of a Column of the Atmosphere.— 
If the tube had an area of exactly one square 
inch, there would be 30 cubic inches of 
mercury in a column 30 inches long ; and 
since the mass of a cubic inch of mercury 
is about half a pound, the whole column 
would have a mass of 1 5 lbs. This column 
would balance a column of air of the same 
area, so that we find that the weight of a 
column of air upon an area of one square 
inch, and extending upwards to the top of 
our atmosphere, is equal to the weight of 1 5 
lbs. when the barometer stands at 30 inches. 
Mercury is a Convenient Liquid for Barometers. — Mercury 



Fig. 62. — The mass of 
a cubic inch of mercurv' 
is i lb. ; therefore, that of 
30 cubic inches is 15 lbs. 



86 ELEMENTARY PHYSICS AND CHEMISTRY. 

is used for barometers for convenience. Since the column of 
mercury which the atmosphere is able to support is 30 inches 
high, it is clear that if a lighter hquid is used, a longer column 
of it would be supported. For example, water is 13! (i3'6) 
times as light as mercury, therefore the column of water which 
could be supported would be 30x131 = 408 inches = 34 feet, 
which would not be a convenient length for a barometer. The 
length of the column of glycerine which can be similarly sup- 
ported is 27 feet. But in ihe case of lighter liquids like these, 
any small variation in the weight of the atmosphere is accom- 
panied by a much greater alteration in the level of the column 
of liquid, and, in consequence, it is possible to measure such 
variations with much greater accuracy. For this reason baro- 
meters are sometimes made of glycerine. 

Pressure of the Atmosphere at Different Altitudes. — Because 
the atmosphere has weight, the longer the column of it there is 
above the barometer, the greater will be the weight of that 
column, and the more it will press upon the meixury in the 
barometer. Hence, as we ascend through the atmosphere with 
a barometer, we reduce the amount of air above it pressing 
down upon it, and, in consequence, the column of mercury the 
air is able to support will be less and less as we ascend. On 
the contrary, if we can descend from any position, e.^^, down 
the shaft of a mine, the mercury column will be pushed higher 
and higher as we gradually increase the length of the column of 
air above it. Since the height of the column of mercury varies 
thus with the position of the barometer, it is clear that the 
alteration in its readings supplies a ready means of telling the 
height of the place of observation above the sea-level, provided 
we know the rate at which the height of the barometer varies 
with an alteration in the altitude of the place. 

At a height of 35 miles from the sea-level, the mercury column 
only stands 1 5 inches high instead of thirty inches, thus showing 
that by rising to that height half the atmosphere is left behind. 
This does not mean that the atmosphere is only 7 miles high, 
for really there is air, though very thin or rarefied, at a height of 
100 or 1 50 miles above the earth's surface. But the air below 
a height of 3^ miles is so much denser than that above this 
height, on account of its being compressed by the air above it. 



WHY THE HEIGHT OF THE BAROMETER ALTERS. 87 

that it produces the same effect as the much greater thickness 
cf hghter air. 

To BE Remembered. 

The pressure of the atmosphere at sea-level is equal to a weight of 
15 lbs. on ever}' square inch. The higher we rise above sea-level the 
less is the pressure. At a height of 33 miles, the mercury column in a 
barometer stands at 15 inches instead of 30 inches. The pressure is, 
therefore, equal to the weight of 75 lbs. per square inch instead of the 
weight of 15 lbs. per square inch. 

Mercury is used for barometers because it is a very dense liquidj 
does not leave a mark upon the tube, and can easily be seen. 

Exercise XXH. 

1. Why does the height of the mercury in a barometer change 
{a) From day to day ; 

(6) When the instrument is taken up a mountain or down a mine ? 

2. What would happen if you were to blow down the small open 
tube of a barometer like that described in the last lesson ? 

3. What is generally about the length of the column of mercury in a 
barometer? If the area of the bore of the barometer tube were one 
square inch, what would be the weight of the column of the mercury 
supported by the air? 

4. Would a barometer made with water as the liquid have to be 
longer or shorter than a mercury barometer? Give reasons for your 
answer. 

5. If you took a barometer up a mountain, what effect would the 
change of level have upon the length of the mercury column? Why 
should there be any effect ? 



ELEMENTARY PHYSICS AND CHEMISTRY- 



LESSON XXIIL 



EFFECTS OF HEAT. 



PRACTICAL WORK. 



Things required. — An iron or brass rod about 6 inches long, 
fitting into a " gauge " cut out of brass, 
as shown in Fig. 63. Spirit lamp or 
laboratory burner. Flat bar of iron 
about I foot long. Two wooden blocks. 
Heavy mass. A straw about 9 inches 
long, fixed at right angles to a sewing 
needle by means of sealing wax. 4 oz. 
flask fitted with stopper and glass tube. 
Jug of hot water. Air ball or paper 
bag. Ice. Porcelain dish or beaker. 
Tripod stand. Iron spoon. Wax (a 
piece of a wax candle will do) or butter. 

What to do. 

Show that the metal rod just fits the gauge. Then heat 
the rod by a spirit lamp or laboratory iDurner. Show that 
it will not now go into the gauge. 




Fig. 63 - -The rod A B will 
fit into the gauge CD when it 
is cold, but it is too large 
when hot. 




Fig. 64.— a flat bar of metal having one end kept from moving by a 
heavy mass is heated, and the other end moves the pointer, because the 
bar gets longer. 



EFFECTS OF HEAT. 



89 



Place the heavy mass on one end of the iron bar resting 

upon one of the blocks, as in Fig. 64. Let the other end 

bear upon the needle placed upon the other block and 

having the straw pointer fixed to it. 

Heat the bar with a flame, and notice 

that the pointer moves on account of 

the expansion of the iron. 

Procure a 4 oz. flask and fit it with 

a cork. Bore a hole through the cork 

and pass through it a long glass tube 

which fits tightly. Fill the glass with 

water coloured with red ink. Push the 

cork into the neck of the flask and so 

cause the coloured water to rise up in 

the tube (Fig. 65). See that there is 

no air between the cork and the water. 

Now dip the flask in warm water, and 

notice that the liquid gets larger and 

rises up the tube. Take the flask out 

of the warm water, and see that the 

coloured water gets smaller as it cools 

and that it sinks in the tube. 

Select an air ball or a well-made 

paper bag and tightly tie a piece of 
tape round the open 
end. Hold the ball 

or bag in front of the fire, and notice 
that the air inside gets larger and in- 
flates the bag. Or, obtain the flask with 
a cork and tube, as in Fig. 66. Remove 
the cork and tube, and, by suction, draw 
a little red ink into the end of the tube 
near the cork. Re-insert the cork and 
gently warm the flask by clasping it in 
your hands. Notice that the air in the 
flask gets larger and pushes the red 
ink along the tube. 
Melt wax or butter in an iron spoon. 
Procure a lump of ice, and notice that it has a particular 




Fig. 65. — An arrange- 
ment for showing that 
liquids get larger when 
heated. 




Fig. 66. —When the 
flask is warmed, the 
air in it gets larger and 
pushes up the drop of 
liquid in the tube. 



90 ELEMENTARY PHYSICS AND CHEMISTRY. 

shape of its own, which, as long as the day is sufhciently 
cold, remains fixed. 

With a sharp brad-awl, or the point of a knife, break the 
ice into pieces, and put a convenient quantity of them into 
a beaker. Place the beaker in a warm room, or apply 
heat from a laboratory burner or spirit lamp. The ice 
disappears, and its place is taken by what we call water. 
Notice the characters of the water. It has no definite 
shape, for by tilting the beaker the water can be made to 
flow about. 

Replace the beaker over the burner and go on warming 
it. Soon the water boils, and is converted into vapour, 
which spreads itself throughout the air in the room and 
seems to disappear. The vapour can only be made visible 
by blowing cold air at it, when it becomes white and visible, 
but is really no longer vapour, but has condensed into small 
drops of water, or, as it is sometimes called, " water-dust '"' 



REASONS AND RESULTS. 

Effects of Heat. — If we make a thing hotter and hotter, we 
are able to notice several changes in it. These changes are of 
three kinds, which we may call : 

( 1 ) Change of size ; 

(2) Change of state ; 

(3) Change of temperature. 

Change of Size. — As a rule, all bodies, whether solid, liquid, 
or gaseous, get larger when heated and smaller when cooled. 

The change of size which a body undergoes is spoken of as 
the amount it expands or contracts ; or heat is said to cause ex- 
pansion in the body. This expansion is regarded in three ways. 
When we are dealing with solids, we find we obtain expansion 
in length or linear expansion, expansion in area or superficial 
expansion, and expansion in volume or cubical expansion. In 
the case of liquids and gases, we have only cubical expansion. 
Jhe same terms can be used with reference to contraction. 

The expansion which substances undergo when heated has 
often to be taken into account. Railway lines, for instance, are 



EFFECTS OF HEAT. 91 

not placed close together, but a little space is allowed between 
the ends of each length of the rails, so that the rails can expand 
in summer without meeting. Steam pipes used for heating 
rooms are also not firmly fixed to the walls at both ends, but 
left slightly loose or are loosely jointed, so that they can expand 
or contract without doing any damage. For the same reason 
the ends of iron bridges are not fixed to the supports upon 
which they rest. Iron tyres are put on carriage wheels by first 
heating the tyre and, while it is hot, slipping it over the wheel. 
As it cools it contracts and clasps the wheel very tightly. 

Change of State. — It has been explained in Lesson III. that 
substances exist in three states, namely, solid, liquid, and 
gaseous. By the action of heat a substance may be changed 
from one state to another. Wax, for instance, is usually a solid, 
but by heating it it becomes a liquid. Butter can in the same 
way easily have its state altered from solid to liquid. Lead 
and zinc are also melted when heated, but they require a hotter 
flame than wax or butter, 

A good example'of the changes of state produced by heat is 
obtained by heating a piece of ice until it becomes water, and 
then heating the water until it passes off into steam or water 
vapour. Here the same form of matter is by heat made to 
assume three states ; in other words, ice, water, and steam are 
the same form of matter in the sohd, liquid, and gaseous state 
respectively. 

Change of state includes changes in the physical condition 
known as liquefaction or becoming fiquid, and vaporisation or 
becoming converted into vapour. Thus, if we heat ice it first 
liquefies or becomes water, and is then vaporised or becomes 
steam. 

Change of Temperature. — Change of temperature is only 
another way of saying that the body gets hotter and hotter. 

If the body is made colder and colder the same changes 
occur, but in the reverse order. We must learn more about 
each of these changes. 

Measurement of Change of Temperature. — The change of size 
which takes place when a thing is heated gives us a good way 
of measuring the change of temperature which it undergoes. 
Think of the experiment with the coloured water in the flask 



92 ELEMENTARY PHYSICS AND CHEMISTRY. 

with a long tube attached to it. Supposing we notice that the 
coloured water in the tube rises through a certain number of 
inches after the water has been heated somewhat ; and that 
we then place the flask mto some other Hquid or some more 
water, and find the water rises up the tube to just the same 
place, we shall have every right to say that the second liquid 
is exactly as hot as the first was. This is measuring its tem- 
perature. The flask and tube with the water have become a 
" temperature measurer, ' or, as we always say, a thermometer. 

To BE Remembered. 

Efifects of Heat. — (i) Change of size, shown by expansion and con- 
traction of solids, liquids, and gases when heated or cooled. 

(2) Change of state, as when ice is converted into water, and water 
into vapour or gas by heat. 

(3) Change of temperature, which means the condition of bodies as 
regards heat, a hot body being at a higher temperature than a cold one. 

Expansion means increase of size. 

Contraction means decrease of size. 

Vaporisation means the change of a liquid into a state of vapour. 

Liquefaction means the change of a solid into the liquid state. 

Exercise XXIII. 

1. Write down the effects which can be noticed when a thing is 
made hotter and hotter. 

2. Describe experiments which prove that things alter in size when 
heated. 

3. What changes do you observe when a piece of ice is placed in a 
glass vessel and heated over a flame ? 

4. How would you show that a bar of iron gets longer when it is 
heated ? 

5. How would you show that liquids expand when heated ? 

6. Describe an experiment which proves that air expands when 
heated. 



THERMOMETERS. 



93 



LESSON XXIV. 



THERMOMETERS. 
PRACTICAL WORK. 

Things required.— Three basins, containing hot, luke-Avarm, 
and cold water. Flask fitted with stopper and tube (Fig. 68). 



THE WATER 

FEELS COLD 

TO THIS HAND 



THE WATER 
FEELS HOT 
TO THIS HAND 




HOT WATER 



LUKEWARM WATER 



COLD WATER 



Fig. 67. — The sense of feeling cannot be depended upon to tell the 
temperature of anything. 

Empty thermometer tube, with bulb. Small cup of mercury. 
Spirit lamp or laboratory burner. Beaker. Flask. 
What to do. 

Arrange three basins in a row (Fig. 

67) ; into the first put water as hot as 

the hand can bear, into the second put 

luke-warm water, and fill the third 

with cold water. Place the right hand 

into the cold water and the left into 

the hot. and after half a minute put 

both quickly into the luke-warm water. 

The left hand feels cold and the right 

hand warm while in the same 

water. 

Place the flask of water, with fitted 

tube, used in the last lesson, in hot 

water (Fig. 68), and notice the height 

of the liquid in the tube. Transfer it to 

cold water, and observe that the liquid m the tube sinks. 




Fig. 68. — When the 
flask is put into warm 
water the liquid in it rises 
in the tube. 



94 



ELEMENTARY PHYSICS AND CHEMISTRY. 




Procure an empty thermometer tube, with a bulb at one 
end. (If a blow-pipe is available, a bulb can easily be blown 

upon one end of the tube by 
melting- the glass in the flame, 
and blowing down the open 
end while the other end is 
molten.) Heat the bulb, and 
while it is hot dip the open 
end in mercury. As the bulb 
cools, mercury will rise in 
the tube to take the place of 
the air driven out by the heat. 



Fig. 69. — After heating the bulb as 
shown, the open end of the tube is 
placed in mercury, which rusnes in 
and fills the bulb and tube. 



Repeat the operation until the mercury 
fills the bulb and part of the stem. 

Place in hot water the bulb of the 
instrument just constructed, and make 
a mark at the level of the mercury in 
the tube. Now place the instrument 
in cold water, and notice that the 
mercury sinks in the tube. The 
mercury is thus seen to expand when 
heated and contract when cooled, and 
if the glass were marked the degree of 
hotness or coldness could be shown by 
the position of the top of the mercury. 

Examine the thermometer supplied. 
Notice that it is similar to the simple 
instrument already described, but the 
top is sealed up, and divisions or gradu- 
ations are marked upon it, so that the 
height of the mercury in the tube can be easily seen. 



I 



Fig. 70. — Sealed tubes 
with mercurj' in the bulbs 
and part of the stem, to 
indicate temperature by 
expansion. 



THERMOMETERS. 95 

REASONS AND RESULTS. 

Feeling- of Heat and Cold. — Some people feel cold at the 
same time that others feel warm. For instance, when a native 
of India, or any other hot part of the earth, comes to England he 
feels cold in ordinai-y weather, while an Eskimo who is here 
at the same time finds the weather warm. You can imagine 
an Indian and an Eskimo meeting an Enghshman. The 
former says, "It is cold to-day," and the latter says, "It is 
hot to-day," while the Englishman thinks the weather is neither 
cold nor hot, but moderate. You can therefore easily under- 
stand that the sense of feeling cannot be depended upon to 
tell us accurately whether the air or any substance is hot or 
cold. Some instrument is needed which does not depend 
upon feeling and cannot be deceived in the way that our 
senses can. Such an instrument is called a thermometer. 

How Expansion may indicate Temperature. — You have already 
learned that substances usually expand when heated and con- 
tract when cooled.- A flask filled with water, for instance, and 
having a stopper through which a glass tube passes, can be used 
to show the expansion produced by heat and the contraction by 
cold. But this flask and tube make but a very rough tem- 
perature measurer. The w^ater does not get larger to the same 
amount for every equal addition of heat. Neither is it very 
sensitive, that ie to say, it does not show very small increases 
in the degree of hotness or coldness, or, as we must now learn 
to say, it does not record verj^ small differences of temperature, 
and for a thermometer to be any good it must do this. Then, 
too, as everyone knows, if we make water very cold it becomes 
ice, which, being larger than the water from which it is made, 
would crack the tube. For many reasons, therefore, water is 
not a good thing to use in a thermometer. 

Choice of Things to be used in a Thermometer. 

I. We Tvant a thins; which expa,ids a great deal for a small 
increase of temperature. 

Gases expand most, and solids least, for a given increase of 
temperature. Liquids occupy a middle place. The most delicate 
thermometers are therefore those where a gas, such as air, is the 
thing that expands. But in common thermometers a liquid. 



96 ELEMENTARY PHYSICS AND CHEMISTRY, 

either quicksilver or spirits of wine, is used. Both these things 
expand a fair amount for a given increase of temperature, and to 
make this amount of expansion as great as possible they are used 
in fine threads by making them expand in a tube with a very 
fine bore. 

2. JVc want a liquid which does not change into a solid unless 
cooled very jntich, nor into a gas unless heated very much. 

We cannot be sure of both these things in the same thermo- 
meter. When we want to use our thermometer for measuring 
great degrees of cold we use one containing spirits of wine, be- 
cause this liquid has to be cooled a very great deal before it is 
solidified, that is made into a solid. But we cannot use this 
thermometer for any great degree of temperature, because it 
changes into a vapour when heated to only a comparatively 
small extent. If we wish to measure higher temperatures we 
use a quicksilver or mercury thermometer, because mercury 
can be warmed a good deal, or, as it is better to say, raised 
to a high temperature, without being changed into a gas, 

3. We must liave our liquid in a fitie tube of equal bore with a 
comparatively large bulb at the end. 

We all know that liquids have to be contained in some sort of 
vessel or else we cannot keep them together. We know, too, that 
we must have a fine bore, so that the liquid may appear to expand 
very much for a small change of temperature. The bore must 
be equal all the way along, that is the width or diameter of the 
inside of the tube must be the same all the way along, so that a 
given amount of expansion in any part of the tube shall mean 
the same change of temperature, and, lastly, there must be a 
large bulb, so that there is a large surface to take the same 
temperature as that of the body the temperature of which we 
wish to measure. 

The Marks on a Thermometer.— We will suppose an instru- 
ment has been made according to the rules just described. 
Before it is of any use it must have divisions marked upon it, or 
be graduated. Sometimes these divisions are marked upon the 
glass of the thermometer, and sometimes upon the wood or 
other material to which the glass is fixed. 

By graduating a thermometer we mean obtaining marks upon 
it to which we can give numbers, so that we can refer to the hot- 



THERMOMETERS. 



97 



ness or coldness, that is, the temperature of any substance, 

b\- means of these numbers or degrees on our thermometer. 

If when a thermometer is plunged into 

water it makes the mercury thread rise 

up to the number 30 on the thermometer, 

we say the water had a temperature of 

thirty degrees, which we should write thus, 

30^. We shall learn in the next lesson how 

these marks are obtained in different kinds 

of thermometers. 

To BE Remembered. 

The sense of feeling does not tell us accurately 
how hot or cold a substance is. 

A thermometer is an instrument for measuring 
the degree of temperature of a substance. 

The liquid in a thermometer should (i) expand 
a great deal for a small increase of temperature, 
(2) not easily change into a solid or gaseous 
state, (3) be in a tube of equal bore having a comparatively large 
bulb at one end. 



Fig. 71. — A therir.o- 
meter with tempera- 
ture divisions marked 
upon the stem. 



Exercise XXIV. 

1. What is a thermometer, and what is it used to measure? 

2. If you were going to make a thermometer, which liquid should you 
use, and why ? 

3. What kind of tube would you select in making a thermometer, and 
why ? 

4. I low would you get mercury into a narrow glass tube having a 
bulb at one end ? 

5. Describe a simple instrument used to measure temperature. 

6. What is the use of a thermometer ? 

7. Why is it not accurate to judge temperature by the sense of feeling? 



98 



ELEMENTARY PHYSICS AND CHEMISTRY. 



LESSON XXV. 



GRADUATION OF THERMOMETERS. 
POINTS. 



FIXED 



observe that as Ions 



PRACTICAL WORK. 

Things required. — Beaker. Flask. Test-tube fitted with 
stopper and exit tube, as in Fig. 72. Ice. Salt. Unmounted 
thermometers, with Centigrade and Fahrenheit graduations. 
What to do. 

Take some pieces of clean ice in a beaker or test-tube 
and plunge a thermometer amongst them. Notice the 
reading of the thermometer ; it will be either no degrees 
(0°) or very near it.' Warm the beaker or test-tube, and 
{ as there is any ice unmelted the 
reading of the thermometer re- 
mains the same. 

Repeat the experiment with 
some other pieces of ice, and 
observe the important fact that 
\ the temperature of clean melting 
ice is the same in all your tests. 
Add salt to the melting ice, 
and notice that the mercury in- 
dicates a lower degree of tem- 
perature. 

Boil some distilled water in a 
flask, test-tube, or beaker, and 
plunge a thermometer in the 
boiling water. Notice the tem- 
perature. Raise the themometer 
until the bulb is just out of the 
water and only warmed by the 
steam. Again record the temperature. In both cases 

lA Centigrade thermometer is supposed to be used. If a Fahrenheit 
thermometer is used the reading will be 32°. 




Pig. 72. — The water in the test- 
tube is boiling. Steam is coming 
out of the tulie, and the thermo- 
meter is being heated by it. 



GRADUATION OF THERMOMETERS. FIXED POINTS 99 

the reading is the same. It is either one hundred degrees 
(100°), or very near it, if you use a thermometer with 
Centigrade divisions. 

Repeat the experiment with a second lot of pure water, 
and note that the temperature of boihng water is again 100°. 

Add salt to the water. Hold a thermometer in the steam 
of the boiling water, and notice that the temperature is 
the same as before, namely 100°. Push the thermometer 
into the water, and notice that a higher degree of tem- 
perature is indicated. 

Again place the thermometer in clean ice in a test-tube 
or flask. Gently heat the vessel, and notice the following 
changes : 

(i) The mercury remains at 0° until the ice is all melted. 

(2) When the ice is melted, the mercury rises gradu- 

ally until it reaches 100°. 

(3) The mercury remains stationary at 100° until all 

the water is boiled away. 

Arrange three basins of cold, luke-warm, and hot water 
side by side. Place the thermometer in the cold water 
and then in the luke-warm water. Notice the temperature 
indicated in the luke-warm water. Now place the ther- 
mometer in the hot water, and when it has been there a 
minute or two put it into the luke-warm water. Notice 
that the temperature indicated is practically the same as 
before. It is thus seen that, unlike our sense of feeling, 
a thermometer is not deceived by being made hot or cold 
before using it to indicate temperature. 

Notice the temperature of the room indicated by the 
thermometer. 

Place the thermometer in your mouth, and notice the 
temperature indicated by it at the moment it is removed. 



REASONS AND RESULTS. 

The Fixed Points on a Thermometer. — It has been proved 
by numerous experiments that the mercur>-, or other liquid, in 
a thermometer always indicates the same temperature when 
placed in ice which is just melting. This temperature, then, 



100 ELEMENTARY PHYSICS AND CHEMISTRY. 

is fixed, and provides us with a fixed point from which the 
divisions upon a thermometer can commence. 

A second fixed temperature, or fixed point, is the temperature 
of the steam of boihng water. The steam of boiling water 
always has the same temperature when the water is boiling, 
and the height of the barometer is 30 inches. It is important 
to remember that this temperature depends upon the pressure 
of the atmosphere, though you may not yet understand why 
this is the case. It is sufficient for the present to know that 
the temperature of the steam of boiling water is a fixed tem- 
perature, and provides the second fixed point upon a ther- 
mometer. 

How the Numbers on a Thermometer are arranged. — It has 
now been explained how two fixed marks, or points, are obtained 
upon a thermometer. The place where the mark near to the 
bulb must be made is found by putting the thermometer into 
melting ice. The mark nearer the other end is got by plunging 
the thermometer into the steam from boiling water. Any 
numbers could be given to these marks. But so that everyone 
shall understand the readings of the temperatures of different 
things, it is best to make the numbering according to an agreed 
plan. 

Centigrade Thermometers. — In scientific work the ther- 
mometer used is called the Centigrade thermometer. This 
name refers to the way in which the fixed points are spoken of 
and the distance between these marks divided. The plan in 
thermometers like these is to call the temperature at which 
ice melts, no dei^rees Centigrade (written 0° C), and the tempera- 
ture at which water boils, one hundred degrees Centigrade 
(written 100° C). The space between the fixed points is then 
divided into one hundred equal parts, and each division called 
a Centigrade degree. 

Fahrenheit Thermometers. — Thermometers in this country 
are generally divided in a different fashion, and so that we 
may know exactly what their readings mean, we must learn 
how the numbers on them are got. The mark obtained by 
putting the thermometer into melting ice is called thirty-twc 
degrees Fahrenheit (written 32° F.), and the mark found by plung- 
ing it into the steam from boiling water, t7vo hinidred and twelve 



CtRADUATION of thermometers, fixed points. loi 



degrees Fahrenheit (212° F.). The space between these fixed 
points is divided into one hundred and eighty (180) parts. The 
illustration (Fig. 73) shows a thermometer 
having Fahrenheit divisions on one side and 
Centigrade divisions on the other, so that the 
two scales can be compared. 

More Remarks on the Boiling Point of 
Water. — We have up to the present pur- 
posely said very little about an important 
fact which must be taken into account when 
marking the boiling point of water upon the 
thermometer. Before water or any other 
liquid can boil when heated in a vessel ex- 
posed to the air, it must give off vapour 
which presses upwards strongly enough to 
overcome the pressure of the atmosphere. But 
as we have learned, the air presses down at 
one time more than at another, and more in 
a valley than up a' mountain. Consequently, 
we shall have to heat a liquid more when 
the atmosphere presses down very much 
than when it is not so heavy, in order to 
make it boil. Water boils at the temperature 
mentioned in our lesson only when the mer- 
cury in a barometer is standing 30 inches 
high. If the barometer shows a higher reading 
than this, water will boil at a higher tempera- 
ture than 100° C, and if the reading is less, the 
water will boil at a temperature less than 100° C. 



Fig. 73. — The num- 
bers on the left of 
the thermometer are 
Fahrenheit degrees 
of temperature, and 
those on the right are 
Centigrade degrees. 



To BE Remembered. 
The fixed points on a thermometer are (i) the 

temperature at which ice melts or water freezes ; 

(2) the temperature of the steam issuing from boiling water when the 

barometer stands at 30 inches. 

Two common kinds of thermometers are (i) the Centigrade and 
(2) the Fahrenheit thernionietcr.s, the different graduations being : 

Centigrade. Fahrenheit. 

Boiling point, 100° 212° 

Freezing point, 0° 32° 



I02 ELEMENTARY PHYSICS AND CHEMISTRY. 

Exercise XXV. 

1. What marks do you find on a thermometer, and how are they 
obtained ? 

2. What do you mean by a " fixed point " on a thermometer ? How 
many are there? 

3. Explain how the numbers on a thermometer are obtained. Write 
down the temperature at which ice melts, and that at which water 
boils. 

4. Some salt water is boiled. What temperature will a thermometer, 
placed in the steam given off, register? Will there be any difference 
in the reading if the thermometer is placed in the liquid ? 

5. What do you know about the temperature of a mixture of ice 
and salt? 



LESSON XXVI. 
. SOLUBLE AND INSOLUBLE SOLIDS. 

PRACTICAL WORK. 

Things required. — Sugar. Salt. Washing-soda. Flasks or 
tumblers with water in them. Spoon. Sand. Camphor. 
Shellac. Spirits of wine. Flowers of sulphur. Carbon bi- 
sulphide. 
What to do. 

Place a piece of sugar in water ; note that it soon dis- 
appears and gives a sweet taste to the whole of the water, 
so that in some way the sugar must have spread throughout 
the water. 

Repeat the experiment with salt, and similarly notice 
that the salt can be recognised everywhere in the water 
by its taste. 

Add sand to water and stir it up with the water. Let 
the water stand for a short time, and notice that the sand 
sinks to the bottom. 

Stir up camphor with water. Notice that the camphor 
does not disappear ; it is insoluble in water. Shake up a 
small lump of camphor with some spirits of wine in a small 



SOLUBLE AND INSOLUBLE SOLIDS. 103 

bottle. It gradually disappears just like sugar does in 
water. 

Shake up flowers of sulphur with carbon bisulphide, and 
notice that it disappears. Be careful to keep the stopper 
in the bottle of carbon bisulphide, and do not bring the 
bottle near a light. 

Fold a piece of clean white blotting paper or a filter 
paper in the manner already explained (Fig. 8). Insert 
the folded paper into a glass funnel and place the funnel 
into a flask. 

Make some muddy water by stirring mud into a tumbler 
of water, or by putting po\sdered charcoal into it. The mud 
or charcoal remains suspended in the water for a long time. 



Fig. 74.— How to pour water into a paper filter in a glass funnel. 

Pour the muddy water carefully on to the filter paper in 
the funnel in the manner shown in Fig. 74, and observe 



I04 ELEMENTARY PHYSICS AND CHEMISTRY. 

that the water which drops through is quite clear. The 
mud is left on the paper. 

Similarly, filter a solution of sugar or salt, and observe 
that the solution is unaltered by passing through the paper. 



REASONS AND RESULTS. 

What Soluble and Solution mean. — When you put sugar 
into a cup of tea and stir it, you know that the sugar disappears. 
How would you find out whether sugar had been put in a cup of 
tea or not ? By tasting the tea. Every child knows that sugar 
gives a sweet taste to tea, water, or milk. If salt is added 
instead of sugar, a salt taste is given to the tea, milk, or water. 
Whenever a substance disappears in a Hquid in this way, and 
yet can be recognised by suitable means everywhere in the 
liquid, it is said to dissolve or to form a solution. Those 
substances which disappear in this way are said to be soluble. 
Many things besides salt and sugar are soluble in water. For 
instance, washing-soda, borax, and nitre (saltpetre) easily 
dissolve, or are soluble in water. Many other things, on the 
contrary, will not dissolve in water, and these are spoken of as 
insoluble substances. 

Substances insoluble in Water. — Among many substances 
insoluble in water are sand, gravel, coal, camphor, and sulphur. 
If you try to dissolve sand, camphor, and sulphur in succession 
in water, you will find that they do not disappear ; hence they 
are insoluble. 

But though camphor will not dissolve in water, yet it dis- 
appears when skaken up in spirits of wine. We consequently 
say that camphor is soluble in spirits of wine, or that we can 
make a solution of camphor in spirits of wine. Another sub- 
stance which will dissolve in spirits of wine and not in water is 
shellac. In fact, some of the varnish which is used for our 
furniture consists of shellac dissolved in spirits of wine. Again, 
if powdered sulphur is shaken up with the bad-smelling liquid 
called carbon bisulphide it dissolves. Though sulphur will not 
dissolve in water, and to only a small extent in alcohol, it forms 
a solution very easily in carbon Iji sulphide. 



SOLUBLE AND INSOLUBLE SOLIDS. 105 

Substances held in Suspension in Water. — Substances which 
are insoluble in water will, if they are very finely powdered and 
stirred up with some water, often take a very long time to settle. 
Or, as it is more commonly expressed, such fine particles remain 
suspended in the water for a long time. The lighter the par- 
ticles are, of course, the longer time it takes for them to settle 
down and for the water to become clear. If on a rainy day 
you take a glassful of muddy water from the gutter, and then 
place it on one side, you will be able to watch the particles 
settling down. Those substances which, like the mud, are 
spread throughout the water without being dissolved in it are 
said to be held in suspension. The rate at which these sus- 
pended particles settle down on the bottom of the tumbler or 
other vessel to form a sediment depends upon their density. 
Light particles take a long time, heavy particles only a short 
time to sink. 

We get rid of Suspended Substances by Filtering. — It is easy 
to separate suspended impurities from water. The process by 
which this is done' is called filtration, or filtering. Many sub- 
stances are used through which to filter water containing 
particles in suspension. Chemists most commonly use paper 
which has not been glazed. As you have learnt, such paper is 
porous. The holes thnjugh it are large enough to let water 
pass, but not large enough to let the suspended substances 
through. In consequence, these particles are left on the paper 
in the funnel, and the water which trickles through is quite 
clear. It must be carefully remembered, however, that it is 
impossible to get rid of substances in solution by filtering the 
liquid. Dissolved material passes through the holes in the 
paper with the liquid in which it is held in solution. 

Other substances besides unglazed paper are sometimes used 
in filtering. Thus the water supply of a town is often filtered 
through beds of sand. Household filters are made with pieces 
of charcoal for the water to trickle through, and in some others 
a particular kind of porous iron or porcelain is employed. 
Even,' filter requires to be cleaned frequently, or it gets clogged 
with impurities from the water which has filtered through it. 



io6 ELEMENTARY PHYSICS AND CHEMISTRY. 

To BE Remembered. 

Solution is the process by which some substances, when placed in 
water or other liquids, disappear, and their particles spread through 
the entire mass of the liquid. 

A substance Is said to be soluble in a liquid when it disappears 
in the liquid and forms a solution. Examples : supar, salt, and soda 
are soluble in water. 

A substance is said to be insoluble in a liquid when it will not 
dissolve in the liquid. Examples : sand, gravel, camphor, sulphur 
are insoluble in water. 

Substances which will not dissolve in water will often dissolve 
in other liquids. Examples : camphor and shellac are soluble in spirits 
of wine ; sulphur is soluble in carbon bisulphide. 

Insoluble substances may be spread throughout water or held in 
suspension. Suspended impurities can be got rid of by filtering. 

Exercise XXVI. 

1. What do you mean by a soluble thing? Give examples. 

2. Explain how you would proceed to make a solution of table salt. 

3. Give a list of as many things as you can which will dissolve in 
spirits of wine and not in water. 

4. How would you obtain clear water from muddy water? 

5. What do you mean by substances being held in suspension in 
water ? 

6. What kind of impurities cannot be got rid of by filtration ? 

7. Explain the terms — soluble, insoluble, filtration, and " held in 
suspension." 



SOLUBLE LIQUIDS AND GASES. 



107 



LESSON XXVII 



SOLUBLE LIQUIDS AND GASES. 



PRACTICAL WORK. 



Things required.— Alcohol, oli\e oil, mercury, ether. Bottle 
of soda-water or other aerated water. Taper. Test-tubes. 
What to do. 

Pour some water into a bottle and then some alcohol,' 
and shake them up together. Observe that the alcohol 
disappears in the water or dissolves in it. 

The same experiment can be performed with oil of 
vitriol. Great care must be taken to pour a small qiianlity 
of the vitriol into water and not water into 
the acid. The acid is dissolved in the 
water. 

Shake up together some olive oil and 
water, and allow the mixture to stand for 
a short time. Notice that the liquids 
separate into two layers, the lighter being 
on the top. Which is the lighter ? 

Repeat the experiment with quicksilver 
and water, and if possible with ether and 
water. 

Examine a bottle of soda-water. Notice 
that it appears clear and bright, and seems 
to have nothing dissolved in it. Uncork, 
or otherwise open it. Bubbles of gas 
escape (Fig. 75). A lighted taper held to the mouth 
of the bottle has its flame put out by the gas which is 
given off. 

' Ordinary methylated spirit will not do, as it forms a niilkiness with water. 
If pure alcohol cannot be obtained, whisky or brandy will do. 




Fig. 75. — Bubbles 
of gas escape from 
a bottle of aerated 
water when the cork 
comes out. 



io8 



ELEMENTARY PHYSICS AND CHEMISTRY. 



REASONS AND RESULTS. 

Solution of one Liquid in another. — The commonest cases of 
solution are when solid substances are dissolved in liquids. In 
addition to this, many liquids will dissolve in other liquids. 
Alcohol and oil of vitriol are examples of liquids which dissolve 
in water. When a liquid dissolves in water, like alcohol and 
oil of vitriol do, we say, in ordinary language, that the two 
liquids mix. This is only another way of saying that they form 
a solution. In the one case, we have a solution of alcohol in 
water ; in the other, a solution of sulphuric acid in water. There 
is still another way of speaking about these cases. It is very 
common to say that we have diluted the acid with water or the 
alcohol with water. 

Liquids insoluble in one another. — If, however, oil, water, and 
mercury, for example, are shaken up together, and then left 

to stand for a time, they will 
be found to separate from one 
another and lie in different layers 
— the mercury at the bottom, oil at 
the top, and water between the two 
(Fig. 76). Here, then, we have 
examples of liquids which do not 
dissolve in one another or do not 
mix. Oil does not dissolve or form 
a solution with water, neither does 
mercury. While some other liquids, 
like ether, dissolve to a small extent 
only in water. Or, we can say, oil 
and water will not mix, quicksilver 
and water will not mix, but ether 
and water partly mix. 
How to separate Liquids which do not mix. — Since liquids 
which do not mix will, if allowed to stand, separate from one 
another, and arrange themselves in layers with the densest 
liquid at the bottom and the least dense on the top, it is 
easy to separate them. All we have to do is to very gently 
tilt the vessel containing them and pour off the top layer. 
This plan is called decanting. Or, we could pour the 
liquids into a funnel supplied with a stop-cock at the bottom. 




Fig. 76. — The liquids in the bottle 
do not mix, and if undisturbed they 
separate into layers — the densest at 
the bottom and the lightest at the 
top. 



SOLUBLE LIQUIDS AND GASES. 



109 




Fig. 77. — A funnel with a tap, for 
drawing off the liquids in it one after 
the other. 



as shown in Fig. -JT, and allow the liquids to arrange them- 
selves in it. Then by turning the stop-cock gently we could 
allow the liquids to run out, one 
after the other, into different 
vessels ; the lowest first, then 
the next, and so on until all the 
liquids have been drained out. 

Some Gases dissolve in Liquids. 
— When a bottle of lemonade, 
ginger-beer, or soda-water is 
opened, a lot of bubbles of gas 
rise out of it. The gas has 
evidently been dissolved in the 
liquid. This is only one of many 
instances of gases which will dis 
solve in liquids. There is a large 
amount of this gas, which ex- 
tinguishes a flame, dissolved in 
soda-water. The drink is called 

"soda-water" because the gas dissolved in the water can be 
made from washing-soda. When you get to know more of the 
science of chemistry, you will learn of m^any other gases which 
will dissolve in water. The liquid sold by chemists as liquid 
ammonia is a solution of ammonia gas in water. 

Importance of Air dissolved in Water. — Rain in falling through 
the air dissolves some of it in its passage to the earth. The air 
which thus becomes dissolved in the water serves a very im- 
portant purpose. Both animals and plants must have air to 
breathe. As 3'ou know ver}' well some animals and plants live 
in water, and these, like those living on land, require air to 
breathe. These water plants and animals depend upon the air 
which is dissolved in the water. When water is boiled, the dis- 
solved air which it contains is driven out of it by the heat. If a 
goldfish were taken out of its bowl and placed in some water 
which had been boiled and allowed to cool out of contact with 
the air, it would die because there would be no air in the water 
for it to breathe. 



no ELEMENTARY PHYSICS AND CHEMISTRY. 

To BE Remembered. 

Some liquids mix or dissolve other liquids. Examples : alcohol 
(whisky or brandy) dissolves in water; so does vinegar. 

Some liquids do not mix, or are insoluble, in one another. Ex- 
amples : oil, water, and mercury. 

Some gases dissolve in liquids. Examples : the gas in soda-water, 
and ammonia gas in the so-called liquid ammonia. 

The air dissolved in water is necessary for the life of water animals 
and plants. 

Exercise XXVII. 

1 . What is really meant when we say two liquids will not mix ? 

2. Give instances of (i) liquids which mix, (2) liquids which do 
not mix. 

3. Will gases dissolve in water? Give reasons for your answer. 

4. How do water animals, like fishes, manage to breathe? 

5. What would you notice if you were to shake (i) some ink and 
water together, (2) some oil and water ? 



LESSON XXVIII. 

THERE IS NO LOSS DURING SOLUTION 
EVAPORATION. 

PRACTICAL WORK. 

Things required. — Salt. Warm water. Balance and box or' 
weights. Flasks. Evaporating basin. Sand-bath or water- 
bath. Tripod stand. Laboratory burner or spirit lamp. 
What to do. 

Put some warm water in a flask, and some sah in a piece 
of paper. Counterpoise the flask of water and the paper 
of salt together, and then dissolve the salt in the water. 
The total mass remains unaltered (Fig. 78). 

Find the mass of a flask of water. Now weigh several 
lumps of loaf sugar, and put this known mass of sugar 



NO LOSS DURING SOLUTION. EVAPORATION, in 

into the water. When the sugar has all dissolved, 
weigh again. Notice that the flask and solution of sugar 
together have a mass exactly as much as the flask of water 
and sugar added together. 




Fig. 78, — There i> no change of mass when s;ilt is dissolved in «ater. 

Dissolve some salt in water, as in previous experiments, 
and place the solution so formed in an evaporating basin, 
and gradually warm 

the basin on a piece C-^ ^'^ 'V, 

of wire gauze, or 
over a sand-bath 
(Fig. 79), until the 
solution boils. (In- 
stead of placing the 
evaporating basin 
in hot sand, it can 
be heated by the 
steam rising from 
boiling water, as 
in Fig. 80.) 

Allow the water 
to slowly boil away. 
When all the water 
has been changed into steam, the salt will be found left 
behind in the bdsin. 

Repeat the experiment in the following manner. Weigh 




Fig. 79.— The shallow basin of water rests upon 
sand kept hot by a burner. The water is drying 
up or evaporating. 



112 ELEMENTARY PHYSICS AND CHEMISTRY. 



out a certain mass of salt in an evaporating basin, and 
dissolve it in water. Heat gently as before. Note that by 
and by a white solid remains in the 
basin. Again weigh. By weigh- 
ing it, we can show that its mass 
is equal to the mass of the basin 
and salt before solution, and it 
is easy to prove that the solid left 
is still salt. 




REASONS AND RESULTS. 

Substances do not lose in Mass 

Fig 8o.-The sh.-xiiow basin has when dissolved. -When a substance 
water in it and is kept hot by the simply dissolves in a liquid, and 

steam rising from the water in the ' -^ • i_ • i 

glass beaker. SO disappears from sight, it almost 

seems as if it is lost altogether. But 
this is not the case. There is no loss whatever. If a cup 
of tea and a few lumps of sugar are weighed separately, 
and then the sugar is put into the tea, their total mass is 
the same as the mass of the tea with the sugar dissolved in 
it. It is very important to remember that there is no change 
of mass when a substance dissolves in water. Though sugar, 
for example, when dissolved in tea or water, disappears from 
sight, it is still in the tea or water as sugar, and we shall see 
later that it can be obtained from the water by proper means. 
The same fact is true of salt and other soluble solids. 

Evaporation.— If a saucer of water is left for a few days, the 
water disappears, or, as is generally said, dries up. The water can 
be made to disappear more quickly by gently heating it. When 
a solution containing salt or sugar is made to dry up in this way, 
the salt or sugar does not disappear, but remains in the saucer. 
The name given to this process of turning a liquid into a 
vapour is evaporation. The solid left behind is spoken of as 
a residue. Because we can recover the solid again by evapora- 
tion, and because there is no change of mass when solution 
takes place, we say that solution is only a physical change 
Salt is not changed into a new substance with new properties 
when it is dissolved in water. When a new substance with 



NO LOSS DURING SOLUTION. EVAPORATION. 113 

new properties is formed by bringing two substances together, 
we have what is called a chemical change. In our later lessons 
we shall have several instances of chemical changes. 

A Practical Application of Evaporation. — In some countries 
where salt does not occur as a mineral as it does in England, 
it is obtained from sea-water. Sea-water contains a large 
quantity of common salt dissolved in it. The sea-water is 
exposed to the heat of the sun's rays in shallow vessels and 
is consequently slowly evaporated. But only pure water passes 
off in the form of a vapour. The common salt and other 
substances in solution in the sea-water are left behind on the 
floor of the shallow vessel, and can be scraped off and collected 
for use. 

In salt-mining, both solution and evaporation are sometimes 
made use of Instead of bringing the salt to the surface in 
lumps, the plan adopted is to flood the mine with water, and 
leave it in the mine for a sufficient length of time for the water 
to dissolve as much of the salt as it can. The solution thus 
formed is then pumped to the surface, and evaporated, when 
the salt is obtained in the same way as in our experiment. 



To BE Remembered. 
Matter is not lost when a substance is dissolved. A solid and 
liquid when separate have the same mass as when the solid is dissolved 
in the liquid. 

Mass of Solid -f- Mass of Solvent = Mass of Solution. 
Evaporation is the process of slowly changing a liquid into a vapour 
by heat. 

Dissolved substances can be recovered by evapoiaiinp the lifuid con- 
taining them. 



Exercise XXVIII. 

1. How would you prove that there is no loss of mass during solution? 

2. How would you obtain the salt from a solution of the salt in 
water ? 

3. What do you know about evaporation ? 

4. Describe some practical applications of the processes of solution 
and evaporation. 

L H 



114 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON XXIX. 

SATURATED SOLUTIONS. 

PRACTICAL WORK. 

Things required. — Alum and nitre. Flasks. Sand-bath. 
Laboratory burner or spirit lamp. Tripod stand. 
What to do. 

Procure a supply of alum or nitre and powder it. Put 
some of the powdered solid into a flask and add water. 
Shake them up together for some time, and if aJl the 
powder dissolves add more and shake again. Continue 
this addition of the powder and the shaking until some 
powder remains undissolved, however much it is shaken. 
You will thus make a cold saturated solution, that is, a 
solution containing as much of the solid as it will hold. 

Now warm the cold saturated solution. The powder 
which before remained at the bottom of the flask dissolves. 
Continue to add more alum or nitre, and notice that a 
great deal must be added before you obtain a hot saturated 
solution. 

Place the hot saturated solution on one side to cool. As 
cooling proceeds, some of the alum or nitre separates out 
in clear, well-formed crystals, because as the solution cools 
it cannot dissolve as much alum as before. 

REASONS AND RESULTS. 

Saturated Solutions. — When any given amount of water has 
dissolved as much of a solid as it can be made to, without 
warming or assisting it in any other way, it is said to be saturated. 
But though cold water, for instance, may be saturated with 
any particular solid, such as sugar, it can, if we warm it, iDe 
made to dissolve more sugar. Though there are some excep- 
tions, it can be regarded as the general rule, that water and 
other liquids will dissolve more of a solid when they are 
warm than when they are cold. In some cases the amount 



SATURATED SOLUTIONS. 115 

of solid which will dissolve goes on increasing as the \\ater 
is made warmer and warmer. In general, therefore, the cooler 
the water the less will it dissolve of a solid. Now suppose 
warm water is given as much sugar, salt, alum, or any substance 
of this kind as it will hold, and is then cooled, what would you 
expect to happen ? It has to give up some of the substance, 
for it cannot hold as much as when it was warm. You may 
have noticed that when your tea has been very sweet, some 
of the sugar is left on the bottom of the cup when the tea 
cools. This is because, though the tea was able to dissolve 
a certain amount of sugar when hot, it could not hold so much 
when cold, and therefore a little of it was deposited upon the 
bottom of the cup. 

Water as a Solvent. — Water dissolves more solids than any 
other liquid which is known. This makes it very useful to 
chemists and others. Water is such a good solvent that it is 
impossible to find pure water anywhere in nature, that is, in 
any stream or lake which we may find in any country. As 
you have learnt, water will not only dissolve solids, but liquids 
and gases as well. As soon as rain is formed from a cloud 
it begins to dissolve some of the gases of the atmosphere, and 
no sooner has it reached the earth than it dissolves all sorts 
of things out of the ground. Of those substances in the soil 
and rocks which are very soluble it dissolves a great deal, 
while of the insoluble things it dissolves either very little, or 
scarcely anything at all, for you must bear in mind that very 
few things are actually quite insoluble. 

The purest water which can be 
got in nature is that collected in a 
vessel, after it has been raining some 
time, before the rain has reached the 
ground. In countries where the rocks 
are very hard and insoluble, and are Fig. 8i.-The ''fur' inside 

' a kettle consists of solids once 

covered by nothing in the way of soil, dissolved in water, and left 

, , . , . 1-1 behind when the water boiled 

the water which is collected is always away. 

very pure compared with ordinary 

water. That many substances are dissolved in ordinary water 

you can see for yourselves if you will examine the inside of the 

kettle at home. There you will find a crust formed by the 




ii6 ELEMENTARY PHYSICS AND CHEMISTRY. 

substances which were dissolved in the water, and have been 
left behind as the water evaporated or boiled away. 

To BE Remembered. 

A solution is saturated with a substance when it contains as much 
of that substance as it will hold at the temperature of the solution. 

The effect of increase of temperature on saturation is usually to 
increase the amount of a substance which can be held in solution. 
The solubility of a substance usually decreases as the temperature is 
lowered. 

Water dissolves most substances, but in different degrees. Salt 
is more soluble in water than sugar, and sugar is more soluble than 
chalk. 

Exercise XXIX. 

1. What is a saturated solution? Describe how to make one. 

2. Which will dissolve more sugar, warm or cold water? What 
is the general rule about the effect of an increase of temperature on 
the dissolving power of water? 

3. What do you know about water as a solvent? 

4. Describe fully what happens if you gradually cool a hot saturated 
solution of alum. 



LESSON XXX. 

SOLUBILITY OF THINGS IN ACIDS. 

PRACTICAL WORK. 

Things required. — Copper turnings, granulated zinc, pieces 
of marble. Nitric, sulphuric, and hydrochloric acids. Test- 
tubes. Evaporating basin, sand-bath, tripod stand, and labora- 
tory burner or spirit lamp. 
What to do. 

Take a few small pieces of copper ; observe their colour, 
and put them into a test-tube and shake up in water. 
They will not dissolve. Now boil the water, and notice 
the copper is still insoluble. 



SOLUBILITY OF THINGS IN ACIDS. 



117 



Throw away the water, and substitute some fairly strong 
nitric acid. {Use the acid with great care, as it is very 
destructive to clothing, and burns the skin.) 

Observe that the copper rapidly dissolves, and eventually 
disappears. Reddish-brown fumes are given off in large 
quantities. When breathed, these fumes are distressing 
and injurious. The liquid changes in colour. At first, 
owing to the solution of some of the reddish-brown gas 
in the liquid, it appears green, but when more water is 
added, the liquid is seen to be of a beautiful blue colour. 

Evaporate some of the blue solution formed in the last 
experiment in an evaporating basin. When it is nearly 
dry,* remove the basin from the source of heat, and set it 
on one side. Carefully notice the blue solid which is 
left behind. It is quite unHke the copper. 

Take some pieces of zinc, and, as in the case of the 
copper, notice their colour, and prove that they are in- 
soluble in water. 

Now pour a -little dilute oil of vitriol (sulphuric acid) on 
them in a test-tube, and notice what happens. The zinc 
rapidly dissolves. Bubbles of gas 
are given off. The solution feels 
very warm. Hold your forefinger 
over the mouth of the tube for a 
minute, and then, after removing 
your finger, bring a lighted taper 
to the tube. There is a slight ex- 
plosion, and the gas which comes 
off burns. {Caution — hold the tube 
with the top pointing away from 
your face. ) 

After the zinc has all dissolved, 
pour off some of the clear liquid, 
and, as before, evaporate it to dry- 
ness in an evaporating basin. A 
white solid is left behind. 

Procure a lump of marble, and break it into small frag- 
' It is not wise to evaporate to complete dryness, as the substance 
which is left behind is easily decomposed by heat. 




Fig. 82. — Dilute oil of vitriol 
and pieces of zinc are in the 
tube. A gas is produced and 
kept in by means of the finger. 
When a light is brought to 
the tube and the finger is 
taken away, the gas burns 
with a slight explosion. 



ii8 ELEMENTARY PHYSICS AND CHEMISTRY. 

ments. Observe that it is very hard. Prove that it will 
dissolve neither in cold nor hot water. 

Pour a few drops of strong muriatic acid (hydrochloric 
acid) into the water, and observe the effervescing, or fizzing, 
which immediately begins. Large quantities of gas are 
given ofF, and the marble gradually dissolves. Place a 
lighted match at the mouth of the test-tube in which the 
experiment is performed. The flame is put out or ex- 
tinguished. 

When all the marble has dissolved, evaporate some of 
the clear liquid left, and examine the white solid which 
remains. It is not marble because it is so soft. Place 
the basin on one side for a time, and observe that this 
white solid takes water out of the air and becomes wet. 
Notice that marble does not do this. 



REASONS AND RESULTS. 

Solution of Another Kind. — In all the instances of solution 
which we have studied before this lesson, there has never 
been a permanent change in the properties of the soluble 
substance, nor has there been any change in mass when the 
thing has dissolved. But these conditions are not always so, 
as we have now to learn. When copper is acted upon by 
moderately strong nitric acid in a test-tube or other glass 
vessel, it rapidly dissolves, and by and by disappears. At the 
same time large quantities of reddish-brown fumes are given 
off. These fumes are very unpleasant to breathe, and, what is 
more, they are very injurious, and should not be allowed to 
escape into a room in any quantity. As the copper dissolves, 
the acid changes colour, and soon appears quite green. But 
this is not the natural colour of the liquid formed as the copper 
dissolves. It is really blue, and appears green because some of 
the fumes get dissolved. If you add some water to the green 
liquid, the blue colour becomes very easily seen. If some of 
this blue solution is slowly evaporated in a basin, you obtain a 
blue residue which is not a bit like the copper you started with. 

This Kind of Solution is a Chemical Change. — This example 
of solution is evidently of quite a different kind from that of 



SOLUBILITY OF THINGS IN ACIDS. 119 

the solution of salt or sugar in water. When sugar is dissolved 
in water, there is no gas given off, and there is no change in 
colour, and, most important of all, we can recover the sugar by 
evaporating the water. The change which occurs when the 
nitric acid is poured on the copper is a chemical change, and it 
is so called because it results in the formation of new substances 
with quite new properties. Copper and nitric acid are not 
at all like the nasty smelling red fumes and the blue solid left 
in the basin. 

Another Instance of the Solution of a Metal where Chemical 
Change occurs. — Though pieces of zinc will not dissolve 
in water, yet if you place them in dilute sulphuric acid they 
dissolve very quickh', and bubbles of a gas which will burn 
are given off. After the zinc has all dissolved, a colourless 
solution is obtained ; and if some of it is evaporated in a basin, a 
white residue is left behind which is in no way like the zinc 
we started with. This, too, is a chemical change, and, as before, 
it is so called, because the solution results in the formation of a 
new substance with new properties. 

Here, using another metal — for copper and zinc are both 
metals — and another acid, you again have a chemical change 
taking place when solution occurs. You know it is a chemical 
change, because the gas which comes off, and burns when 
a lighted taper is put to it, and the white solid left in the 
basin are not at all like the zinc and the acid with which you 
started. 

Other Substances besides Metals will dissolve in Acids. — 
Metals are not the only things which will dissolve in acids. 
Though marble, like copper and zinc, is insoluble in water, it 
will dissolve in some acids, for instance muriatic or hydrochloric 
acid. This is another example of solution. The acid is the 
solvent and the marble the soluble substance. And this 
solution also has been accompanied by a chemical change, 
because the white soft solid which becomes wet in the air, and 
the gas which is given off and puts out a flame, are quite 
unlike the hard marble and the liquid acid. 



I20 ELEMENTARY PHYSICS AND CHEMISTRY. 

To BE Remembered. 

Certain Metals dissolve in Acids. — In this case the process is accom- 
panied by the formation of new substances with new properties. It is 
therefore an example of a chemical change. 

In this way copper dissolves in nitric acid, and zinc in dilute 
sulphuric acid. 

Other substances besides metals will dissolve in acids. The solution 
of marble in hydrochloric acid is an example. This is also an instance 
of a chemical change. 

Exercise XXX. 

1. Describe the appearance of copper and zinc. 

2. How would you prove that copper is insoluble in water ? 

3. Describe fully what takes place when moderately dilute nitric 
acid is poured upon copper. 

4. What do you know about the gas which is given off when dilute 
sulphuric acid is poured upon zinc ? 

5. How would you show that a new substance is formed when 
hydrochloric acid dissolves marble ? 



LESSON XXXI. 

CHANGES OF MASS WHEN CHEMICAL ACTION 
ACCOMPANIES SOLUTION. 

PRACTICAL WORK. 

Things required. — As in the last lesson, with balance and 
box of weights. 
What to do. 

Repeat the experiments with copper and nitric acid 
described in the last lesson ; but before adding the acid 
determine the mass of the copper used. Evaporate to 
dryness the whole of the coloured liquid obtained by dis- 
solving the copper in an evaporating basin, the mass of 



CHANGES OF MASS. I2I 

which has been determined by previous weighing. When 
the basin is cool, weigh again, and, allowing for the mass 
of the basin, observe that the mass of the blue residue 
is greater than that of the copper taken. 

Similarly repeat the experiment with the zinc and dilute 
sulphuric acid. In the same way show that the mass 
of the white residue obtained is greater than that of the 
zinc with which the experiment was started. 

Repeat the experiment with marble and hydrochloric 
acid. Show that the mass of the white residue left in 
the basin is greater than that of the marble acted upon 
by the acid. 

[A few hours before the next lesson a warm saturated 
solution of alum should be made and put by to cool. The 
reason for this will be seen on p. 124.] 

REASONS AND RESULTS. 

Changes in Mass when a Chemical Change accompanies 
Solution. — You have already learnt that one of the reasons 
for saying that a physical change occurs when a solid is dis- 
solved in water, is because there is no change of mass. But 
whenever a chemical change takes place at the same time as 
the solid dissolves in a liquid, as in all the experiments we 
have had in this lesson, there is a most decided change of 
mass. This is a very important difference between physical 
and chemical changes, and it is very necessary that you should 
thoroughly understand it. 

The Case of Copper and Nitric Acid. — If a piece of copper, 
the mass of which has been found by weighing to be one gram, 
is dissolved in moderately dilute nitric acid, and then the whole 
of the blue solution obtained is evaporated very carefully, so 
that none of it is lost, the mass of the blue residue left behind 
will be found as nearly as possible three grams. It is quite 
clear that all this cannot be copper. Indeed its appearance is 
quite enough to tell you that it is not copper. But it contains 
copper, and when you have learnt more about chemistry you 
will know the way in which the copper can be obtained from 
it. What has really happened is that the copper has combined 



122 ELEMENTARY PHYSICS AND CHEMISTRY, 

or united with a part of the acid to form a new substance. 
The blue residue is made up of the copper you started with 
and a part of the acid as well. This explains why the mass 
of the residue is greater than that of the copper alone. 

The Case of Zinc and Sulphuric Acid. — The experiment 
with zinc and sulphuric acid teaches just the same important 
lesson. If a piece of zinc, the mass of which is one gram, be 
completely dissolved in dilute sulphuric acid, and the whole of 
the solution thus obtained be evaporated to dryness, and the 
mass of the residue determined, it is found that just about 
two and a half grams of the white solid have been obtained. 
In this case, too, the metal combines or unites with a part of 
the acid to form the new substance left behind in the basin. 
By proper means it would be easy to again obtain the zinc from 
the white residue. 

The Case of Marble and Hydrochloric Acid. — What you 
have now learnt about these changes in mass when metals are 
dissolved in acids is also true when things which are not metals 
are dissolved in acids. Marble is not a metal, but it easily 
dissolves in acids, for instance, hydrochloric acid. If, as before, 
one gram of marble is dissolved in as much hydrochloric 
acid as is necessary, and the whole of the solution is evaporated 
in a basin, it is found by weighing that the mass of the white 
residue left behind in the basin is more than one gram, but 
not so much more as in the case of the copper or the zinc. 1 he 
mass of the white residue left behind when the solution 
obtained by dissolving the marble in hydrochloric acid is 
evaporated is about one and one-tenth grams (i^\j grams). 

The Total Mass is unaltered. — Returning to the consideration 
of the solution of copper in nitric acid, and taking other things 
into account, there are more facts to be learnt from it. If, in 
addition to ascertaining the mass of the copper by weighing, 
that of the nitric acid is also found, and these two masses are 
added together, a certain mass is obtained. Now, chemists 
discovered a long time ago that the total mass obtained in this 
way is the same as is got by adding together the masses of the 
blue residue left in the basin, all the gas which is given off, 
and all the steam which escapes when the blue solution is 
evaporated. 



CHANGES OF MASS. 123 

These facts can be put down in the form of addition sums as 
below : 

Examples ok Chemicai, CitANOE. 
Before, After. 

Mass of Copper. 1 J Mass of Blue Residue. 

Mass of Nitric Acid. f \ J^^' °J ^^e gas given off. 

) \ Mass 01 hteam. 

Total Mass is equal to Total Mass. 



Mass of Zinc. ) J Mass of White Residue. 

Mass of Sulphuric Acid. \ \ ^?^^^ °J ^^ ^^^^^ b"™«- 
^ ) \ Mass of hteam. 



Total Mass is equal to Total Mass. 



Mass of Marble ) f Mass of White Residue. 

w^^c „f i-r.,^,„Ai-.„-„ \„;a r "! Mass of Gas which puts out flame. 

Mass of Hydrochloric Acid. [ ) 5^^ ^f gteam. 

Tqtal Mass is equal to Total Mass. 



To be Remembered. 

When chemical action accompanies solution, changes in mass 
occur. Thus, the blue residue in your experiment weighs more than 
the copper, and the white residue more than the zinc, when these 
metals are dissolved in acids. 

The total mass of the new substances oVjtained when a chemical 
change lakes place is the same as that of those originally taken. Thus, 
if the masses of the copper and nitric acid be added together, the same 
result is obtained as by adding the masses of the blue residue, the 
gas given off, and the steam. 

Exercise XXXI. 

1. Will the Vjlue residue obtained by evaporating a solution of copper 
in nitric acid have the same mass as that of the copper ? Give reasons 
for your answer. 

2. WTiat amount of white residue can be got by dissolving one gram 
of zinc in dilute sulphuric aci'l and evaporating the solution obtained ? 
Why is its mass greater than that of the zinc ? 

3. What changes in mass do you know of which occur when marble 
is dissolved in hydrochloric acid ? 

4. How would you show that there is no loss in the total mass when 
a chemical change occurs ? 



124 ELEMENTARY PHYSICS AND CHEMISTRY. 

LESSON XXXIL 
CRYSTALS AND CRYSTALLISATION. 

PRACTICAL WORK. 

Things required. — Crystals of washing-soda, sugar candy, 
borax, rock-crystal, blue vitriol, rock-salt, and alum. Flasks. 
Sand-bath. Laboratory burner. Tripod stand. Blotting paper. 
Test-tubes. 
What to do. 

Examine as many crystals as you can and draw them. 
Write down the number of faces each has. 

Make a warm saturated solution of alum as described 
in Lesson XXIX. While it is still hot shut the mouth of 
the flask with a cork, or cover it with a piece of suitably 
folded paper, and set it on one side to cool. After a few 
hours, crystals of alum will be found to have separated out. 

When the solution of alum, described in the last ex- 
periment, has become quite cold, and the crystals there 
referred to have separated out, carefully pour off the liquid 
from the crystals, and allow these to gently slide on to a 
piece of clean white blotting paper. Shake them on the 
blotting paper, and, if possible, dry them without handling. 

Now take a small crystal and heat it gently in a clean, 
dry test-tube. Notice that it melts and gives off steam 
which condenses on the sides of the tube near the top 
in the form of water. When cold, the alum is seen to have 
lost its shape. 

Heat a crystal of blue vitriol in a test-tube, and show 
that the shape and colour are lost as the water is driven 
out of the crystal. It regains its blue colour if water is 
dropped upon the powdery lump. 

Inspect some clear crystals of soda (sodium carbonate), 
and also some which have been exposed to the air and 
become white and powdery. 



CRYSTALS AND CRYSTALLISATION. 



125 



REASONS AND RESULTS. 

Crystals. — When substances are found in lumps hav 
regular shape, which is always the 
same for the same kind of thing, 
it is said to be found in crystals, 
or to be crystalline. Generally the 
shapes which crystals have are well- 
known forms in geometry. Thus 
some crystals are known which are 
perfect cubes (Fig. 88), such as 
crystals of rock-salt, fluorspar, iron 
pyrites. Sometimes the crystal has 
eight sides, like the solid known as 
the octahedron (Fig. 85). The 
diamond is sometimes found having 
this shape. Rock-crystal has gene- 
rally six sides, and a si.x-sided pyra- 
mid at one or both ends (Fig. 84). 
When you get on farther with your 
study of science, you will learn that 
crystals can all be divided into six 
classes, every member of each class 

or family having something about ^no^nc^^ys^aUineSbstance.' 

its shape the same. ?, photograph by Mr. 

'^ Hadley.) 




a com- 
(PVom 
H. E. 




Fig. 84.— Group of rock-cri'Stals 
Museum. 



From a Report of the U.S. National 



126 ELEMENTARY PHYSICS AND CHEMISTRY, 




Fig. 85. — An eight-sided crystal of alum. 
(From a photograph by Mr. H. E. Hadley.) 



How Crystals can be made. — Warm water when saturated 

with any soluble substance, 
as you learnt in a previous 
lesson, often contains more 
of the solid dissolved than 
an equal quantity of a cold 
saturated solution. The con- 
sequence of this is, that if 
you allow a warm saturated 
solution to get cold, the water 
can no longer keep all the 
substance in solution, and it 
separates out in the solid 
state, which, under these cir- 
cumstances, always takes a 
crystalline character. The 
crystals of alum, formed in this way, generally have eight 
sides, or the shape of the crystal is the same as the solid 
called the octahedron, shown in Fig. 85. But in some cir- 
cumstances the crystals only have six sides, or are cubes. 

Some Crystals contain V/ater. — By heating a crystal of alum 
or iDlue vitriol in a clean dry test-tube, it is easy to show that 
they both contain water. This water is given off in the form of 
steam, which condenses into drops of water on the cold upper 
part of the tube. There are many other crystals besides those 
of alum and blue vitriol which also contain water. This water, 
which is contained in some crystals, is known as ■water of 
crystallisation. It is necessary for these crystals to have this 
water in them to form the regular shape of which you have 
learnt. If the water of crystallisation is got rid of they become 
powdery. Some coloured crystals not only lose their shape 
but also their colour when the water of crystallisation is driven 
out. Other crystals again, if simply exposed to the air, lose 
this water and become powdery. Such crystals are said to 
be efflorescent, and crystals of soda are a good example 
(Figs. 86 and 87). Other substances do just the opposite thing 
and take up more water from the air, becoming very moist. 
These are called deliquescent. The white residue obtained by 
evaporating the solution formed when marble is dissolved in 
hydrochloric acid is a deliquescent substance. 



CRYSTALS AND CRYSTALLISATION. 127 

To BE Remembered. 

Crystals are naturally formed lumps of certain substances having a 
regular shape, which is always the same for the same kind of thing. 

Rock-salt and some other substances form crystals which are perfect 
cubes. The diamond crystals have the shape of the octahedron. 

Crystals can be made by allowing a warm saturated solution to cool. 

Water of crystallisation is the water contained in some crystals. 
It has something to do with their shape and sometimes with their colour. 

Efflorescent crystals easily give up their water of crystallisation to 
the air. 

Deliquescent substances readily take up moisture and become wet. 

Exercise XXXIT. 

1. Name six crystalline solids. 

2. Give the name of a crystal which has six sides, and one which 
has eight sides. Make a drawing of each kind. 

3. If you were given some powdered alum, explain how you would 
proceed to make a crystal of alum. 

4. How would you show that crystals of alum contain water ? What 
is the water called ? 

5. What do you mean by an efflorescent crystal ? Name one. 

6. What happens to a crystal of blue vitriol if it is heated in a 
test-tube ? 

7. Write down all you know about a crystal of rock-salt. Draw 
such a crystal. 



ELEMENTARY PHYSICS AND CHEMISTRY. 



LESSON XXXIII. 




CRYSTALS AND CRYSTALLISATION— Continued. 
PRACTICAL WORK. 

Things required. — Crystals of washing-soda, sugar candy, 
borax, rock-crystal, blue vitriol, rock-salt, and alum. Flasks. 

Sand-bath. Laboratory 
burner. Tripod stand. 
Blotting paper. Magnify- 
ing glass. Evaporating 
basin. Sulphur. Iron 
spoon. Test-tubes. 

What to do. 

Evaporate a solu- 
tion of common salt 
by gently heating it, 
and, when the basin is 
dry, examine a little 
of the residue. Care- 
ful inspection will discover small cubes, the shape of some 
of which can be recognised by the unaided eye. The 
cubical shape of the 
others can be easily 
made out under a 
magnifying glass. 

Heat some of the 
dry powder in a test- 
tube. Notice the 
crackling and the 
absence of water on 
the side of the tube. 



Fk;. 86. --A group of fresh crystals of 
washing-soda. Notice how clear the crystals 
are. (From a photograph by Mr. H. E. 
Hadley.) 



Make a hot satur- 
ated solution of soda, 
just as you did in the 
case of the alum in 




Fir.. 87. — The .same croup of crystals as in 
Fig. 86, which have effloresced after exposure 
to the air for a short time. Notice the changed 
appearance. (From a photograph by Mr. 
H. E. H.-idley.) 



CRYSTALS AND CRYSTALLISATION. 129 

Lesson XXIX. Put the solution, when you have made 
quite sure that it will dissolve no more, on one side to 
cool. Large clear crystals will be formed. 

Make a similar saturated solution of soda, and having 
poured some into an evaporating basin, float the latter on 
cold water in a bucket so that it shall cool more rapidly. 
Observe that the crystals formed are much smaller than in 
the last experiment. 

Take one of the large, clear crystals previously obtained, 
and dry it on clean, white blotting paper, and heat it in a 
tube, if necessary breaking the crystal to get it in. Observe 
the steam given off, the water which collects, and also 
the white powder left behind. 

Melt some powdered sulphur in an iron spoon or cup, and 
then allow it to cool slowly. When a solid crust has been 
formed over the top, make two or three holes in it, and pour 
off the remaining liquid sulphur. When the sulphur is cool, 
examine the inside of the spoon or cup, and notice the fine 
needle-like crystals of sulphur (Fig. 89). 

Having melted some sulphur as in the last experiment, 
pour the liquid sulphur into some cold water. Examine the 
product formed, and observe it has still a crystalline 
appearance ; the crystals are so small that individual 
crystals cannot be distinguished. 

REASONS AND RESULTS. 

Crystals of Common Salt. — Salt 
crystallises in six-sided solids, 
or cubes (Fig. 88). When the 
crystallisation is brought about by 
evaporating a solution of salt, the 
crystals are very small. Some 
natural crystals, known as rock- 
salt, are however of quite a large 
size. There is no water of crystal- 
lisation in crystals of common salt, 
and when they are heated no steam /""• ^^--^ ^iy^ided crystal 

•' of common salt. (iTom a photo- 

is given off. The crackling which s'^ph ty Mr. H. E. Hadley.) 

I. I 




I30 



ELEMENTARY PHYSICS AND CHEMISTRY. 



is noticed when crystals of salt are heated in a tube is spoken of 
as decrepitation, and is due to the breaking-up of the crystal 
into fragments. 

Crystallisation of Soda. — Soda, as it is called in ordinary 
language, or sodium carbonate, as it is known to the chemist, 
is a common substance, both in the crystalline condition or in 
the form of white powder, as the carbonate of soda, which is 




Fig. 89.— Needle-shaped crystals of sulphur. (From a photograph by 
Mr. H. E. Hadley.) 



used for various purposes in our houses. The difference 
between the white powder which is perhaps best known, and 
the crystalline form, is the water of crystallisation which the 
crystals contain. We can easily obtain crystals if we have a 
supply of the powder, by making a warm saturated solution of 



CRYSTALS AND CRYSTALLISATION. 131 

the powder and allowing it gradually to cool, for then large 
crystals will separate out. 

If, however, the warm saturated solution is cooled quickly, by 
placing the vessel containing it into cold water, the crystals 
rapidly separate, but are of much smaller size. This difference 
is true of most saturated solutions ; indeed, whenever crystals 
are formed by cooling, we may expect them to be of a large size 
only when the cooling takes place slowly; if heat is given up 
rapidly the crystals formed are always small. 

Some Crystals can be made in Another Way. — Other crystals 
besides those of common salt have no water in them. Many of 
these can be made in another way. One kind of sulphur 
crystals is a good example. When some powdered sulphur 
(milk of sulphur) is melted in a large iron spoon, or ladle, over 
a gas flame, and the melted sulphur is allowed to cool slowly, 
a solid crust is gradually formed on the top. If, as soon as 
this happens, two or three holes are made in the crust and the 
remaining, still liquid, sulphur is poured off, it will be found on 
examining the inside of the ladle that fine needle-like crystals of 
sulphur have been left behind. These, like all crystals, have 
smooth flat sides and sharp straight edges. 

In this case, too, there is a difference when the melted sulphur 
cools very rapidly. The quick cooling can be conveniently 
brought about by pouring the melted sulphur into cold water. 
If this is done, the crystals formed are so small that individual 
examples cannot be distinguished, though the solid sulphur is 
seen to have a crystalline appearance. 

To BE Remembered. 

Crystals of common salt have the form of cubes. 

Decrepitation is the crackling sound produced by the breaking up 
into fragments of waterless crystals. 

Soda crystals can be obtained from ordinary washing-soda by making 
a saturated solution of the powder and allowing it to cool. 

Two examples of waterless crystals are common salt and sulphur. 

Sulphur crystals can be obtained by melting sulphur and pouring 
out the liquid sulphur from the interior after a crust has been 
formed. 



132 ELEMENTARY PHYSICS AND CHEMISTRY. 

Exercise XXXIII. 

1. What differences would you observe if you heated salt crystals and 
crystals of soda in different test-tubes ? 

2. Explain how you would make some crystals of sulphur. 

3. Describe how to make soda crystals from powdered carbonate of 
soda. 

4. How does a crystal of salt differ in shape from a crystal of soda? 

5. Explain how to obtain a crystal which has no water in it. 

6. Why is steam given off when crystals of soda are heated, but nor 
when crystals of sulphur are heated ? 



GRAPHIC REPRESENTATION. 



133 



LESSON XXXIV. 



GRAPHIC REPRESENTATION. 



PRACTICAL WORK. 

Things required. — Squared paper, or chequer drawing book 

such as is used for Kindergarten drawing. Ruler and pencil. 
What to do.» 

Draw in pencil, upon chequer or squared paper, or upon 
Fig. 90, hues to represent the densities of the substances 
named in this figure. The line to represent the density of 
water, that is, i, is already drawn. Starting from the up- 





— 




n 


n 


■ — 




— 


— 


— 


— 




























































































































































































































(^npPFR 
















































Iron 
































































































Mmubii 
















































WAT£ft 


















































1 2 3 4- 5 6 7 8 9 10 II 12 13 14- 15 re 17 18 19 20 21 22 || 



Fig. 90 — Copy this figure and draw lines upon your sketch to repre- 
sent the numbers given in the table of densities. 

right line at the end of each name, draw a horizontal line 
for each substance, making the lines of the lengths given 
in the following table : 

Tablk of Densities. 

Marble, - - 2|. Silver, - - lo^. 

Diamond, - - 3^. Lead,- - - ii|. 

Iron, - - - l\- Gold, - - - I9- 

Copper, ■ - 8f. Platinum, - - 22. 

Find the number of boys present in the class on the last 
twenty times the register of attendance has been marked. 

1 Before doing these exercises it is advisable to read through the lesson. 



134 



ELEMENTARY PHYSICS AND CHEMISTRY. 



Write down the numbers. You should now plot these 
upon the squared paper in Fig. 91. The numbers at the 
feet of the upright Hnes refer to the days of the register, 
and the numbers at the ends of the horizontal lines refer 



razr 

29 
28 
27 
ZB 
2S 
24 
23 
22 
21 
20 
19 

la 

17 
16 
15 
I'h 
13 
12 
II 
K) 
9 

a 

7 
€ 
S 
* 
3 
2 
7 






































































































































































































































































































































































































































































































































































































































































































































































































































































































































■ 


















































































































































































































































































































































































































































1 2 3 ^5 6 7 S 9 10 II IZ 13 /f /5 /6 17 /8 13 ZO 21 22 11 



Fig. qi. — A sheet upon which the attendances of pupils at different 
times can be plotted. 



to the number of boys present. If 15 were present at the 
first time selected, put a dot at the number 15 upon the 
first upright line; if 21 were present at the second time, put 
a dot on the same level as 21, upon the second upright 
line ; and so on for all the twenty times the register was 
marked. 



GRAPHIC REPRESENTATION. 



135 



Upon Fig. 92 and Fig. 93, or on a sheet of squared paper 
marked in the same way, represent the following readings 
of a certain barometer and thermometer in the month of 
March : 



Date. 


Barometer. 
Inchej 


Thermometer. 
Fahrenheit Degrees 


larch I, 


29-5, 


437- 


2, 


297, 


39-5- 


3, 


- 287, 


38-6. 


4, 


29-3, 


- - 42-8. 


5. 


29-2, 


427. 


6, 


29-6, 


39-I- 


7, 


29-9, 


- - 367. 


8, 


30 'O, 


40-8. 


9. 


30-0, 


41-4. 


10, 


29-9, 


45-I- 


II, 


30-0, 


46-2. 


12, 


29-5, 


43'4- 



To do this for the readings of the barometer, look at the 
left-hand side of the squared paper for the corresponding 



Jh 








-_ 






- 


- 


- 




- 








-1 




r- 




- 


- 






- 




r 




- 


- 


- 




- 






^ 


- 




-■ 




- 






- 




- 














































































































































































































































































































































































































































































































































































































































































































































































































































































^ 3 J 














































































































































































































































































































































































































































































































































































UJ 




























































































H J 


























































































































































































































































































S 2 J 






















































































































































































































































































































































































































































































































































































































































































h 


















































































































































































2sL 








u 


LLI 




L 




U 


u 


L 








Ll 


L 




L 


L 






-U 




u 




u 


L 


u 




-Li 






U 


u 










h 






JJ 




LL 


UJ 



DAYS OF THE MONTH. 

Fig. 92. — A sheet upon which the rise and fall of the mercury in a 
barometer can be shown. 



height of the barometer, and, when you have found it, make 
a dot at that particular height upon the line corresponding 
to the day of the month. Repeat the operation for every 
day, and connect consecutive dots with a straight line. 



136 ELEMENTARY PHYSICS AND CHEMISTRY. 

The irregular line or curve thus produced shows at a 
glance the variations of atmospheric pressure. 





























































3I0I 1 1 1 M 1 1 ill M 1 1 1 1 1 III 1 1 III 1 1 II 1 1 1 1 1 1 1 1 III 1 1 III 1 1 III 1 1 III 1 1 , 1 



DAYS OF THE MONTH. 

Fig. 93. — A sheet upon which the rise and fall of temperature during 
a month can be shown. 

In the case of the thermometer the degrees are shown at 
the left-hand ends of the horizontal lines of the squared 
paper, and the days of the month are shown at the bottom 
of the vertical lines. 



REASONS AND RESULTS. 

Representation of Quantities by Numbers. — Up to the present 
all quantities have been represented by numbers. Thus, in one 
lesson, in recording the volumes of different solids, these quan- 
tities were expressed by saying how many cubic centimetres or 
cubic inches each solid contained. In another lesson the 
number of times heavier a certain volume of a substance was 
than an equal volume of water, that is, the relative density of the 
substance, was similarly expressed by a number, and in this 
way a table such as the following was obtained : 

Water at 4° C. = 1. 



Wood (Oak), - 


0-85 or 


hi 


Copper, - 


- 875 or 8f 


Glass, 


275 or 


2f. 


Silver, - 


- 10-5 or io| 


Diamond, 


3'5 or 


3*. 


Lead, 


- 1 1-5 or iii 


Zinc, 


7-0 or 


7- 


Gold, - 


- l9'o or 19. 


Iron, 


7-5 or 


7i- 







GRAPHIC REPRESENTATION. 



137 



Other instances where quantities have been expressed by 
numbers you will remember for yourselves. Now the question 
arises, Is there no other way in which quantities like these could 
be compared more easily ? There is. We can represent them 
by hnes of different lengths. 



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1 



























Water Zioc Iron Copper Silver Lead Gold 

Fig. 94. — (From Gordon's Practical Science.) The lengths of the 
thick upright lines show the relative densities or specific gravities of the 
substances named at the bottom. 

Representation of Quantities by Lines of Different Lengths. — 
Suppose you want to represent the numbers in the table on p. 136, 



138 ELEMENTARY PHYSICS AND CHEMISTRY. 

which tells us how many times heavier several substances are 
than an equal volume of water, by using lines of different lengths, 
you would proceed like this. Fix upon some convenient length 
to represent the standard density, namely that of water. Suppose 
you take the lengths of the sides of two adjoining squares on a 
piece of squared paper to represent the density of water, and 
then thicken the sides of these squares as in Fig. 94. All you 
have to do now is to make a mark, at a distance above the 
bottom line of the piece of squared paper shown in the diagram, 
equal to the number of sides of squares which are necessary to 
represent the numbers in the table when the sides of two squares 
equal the number i. To make this very easy the numbers 
arranged on this plan are placed on the left-hand side of the 
piece of squared paper. Thick lines are drawn from the points 
so obtained to the bottom of the paper. The relative densities 
of zinc, iron, copper, silver, lead, and gold are shown in the 
diagram. You should read off the numbers which the lengths of 
these lines represent and compare them with those in the table. 
Graphic Representation. — A plan such as that described in 
the last paragraph is a simple case of what is known as graphic 
representation. This way of representing quantities which we 
wish to compare is often very much simpler than only using 
numbers. We are able to see the relation which the numbers 
bear to one another at a glance. Graphic representation is 
always employed to record the readings of the barometer and 
thermometer. 

Daily Weather Records. — Most sharp boys and girls have 
noticed, either when at the sea-side or in some public park or 
other, that there is often a collection of instruments of different 
kinds for observing facts about the weather. Among these 
instruments there is always a barometer and a thermometer. 
It is very important to know what the weight of the atmosphere, 
or, as we have learnt to call it, the pressure of the atmosphere, 
has been every day and throughout each day ; and also what 
the temperature has been, that is, how cold or how warm the 
air has been. It is becoming more and more common in all 
sorts of places to make arrangements for observing these facts 
every day, and also for having a careful account kept of them. 
The records can be kept in various ways. 



GRAPHIC REPRESENTATION. 



139 



How Records of Pressure and Temperature can be kept. — 

The first plan for keeping a record of these pressures and 
temperatures which would occur to anybody would probably be 
to make some sort of diar}^, and to write down each day, say at 
nine o'clock in the morning and six o'clock in the evening : 
Pressure ... so many inches on the barometer ; Temperature 
... so many degrees on the thermometer. Thus : 

October 26th, 1898. 

Pressure. Temperature. 

9 a.m. - - inches. 9 a.m. ° C. ° F. 

6 p.m. - inches. 6 p.m. " C. ° F. 

But at the end of a week or month, when )ou wished to 
compare the readings of the diffe- 
rent days, it would take too much 
time and thought to make such a 
comparison. Though at the time 
of observation the pressure and 
temperature may. be written down 
in the diary form, it is best to 
arrange the readings in a different 
manner when they have to be 
compared. The plan adopted will 
now be explained. 

Graphic Plan of showing Tem- 
peratures. — You know that the mer- 
cury in a thermometer expands with 
heat and contracts with cold. The 
number against which the top of 
the mercury in a thermometer 
stands depends, therefore, upon 
the condition of the weather as 
regards warmth or cold. The 
seven illustrations of a thermo- 
meter in Fig. 95 show the tem- 
perature indicated by a certain 
thermometer at 8 a.m. on the 
first seven days of a certain month 





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Fig. 95. — To show the position 
of the mercury in a certain thermo- 
meter on seven different days. 



A dotted line has been 
drawn from the point at which the top of the mercury 



I40 ELEMENTARY PHYSICS AND CHEMISTRY. 



90 
SO 

10 
60 

50 

^ 

30 
20 
10 






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1 2 3 ^ 5 6 7 \ 



Fig. 96. — The upright lines re- 
present the mercury in a thermo- 
meter on seven different days. 
Notice the broken line connecting 
the tops of the mercury columns. 



Stood on each day to that which it occupied the next day, 
so that you can see at once whether there was a fall or a 

rise of temperature from one day 
to another. The line is, in fact, 
a graphic representation of the 
changes of temperature from day 
to day. 

Now, it is easy to understand 
that if you wish to represent 
temperatures by a line it is 
not necessary to draw a thermo- 
meter for each day. You 'can 
take a sheet of paper similar 
to that shown in Fig. 96, and 
mark at the side numbers like 
those upon the thermometer, 
while along the bottom the days 
of the week or month can be 
put. The thick vertical lines 
in this diagram may thus be imagined to represent the 
mercury in the thermometer on the same days as before, 
and the line joining the tops is, 
therefore, just like that shown in 

Fig. 95- 

But it is not necessary even 
to draw the thick upright lines. 
A simpler plan is to put a dot 
at the point where the top of 
the mercury stands day by day, 
and then the dots can after- 
wards be connected, as shown 
in Fig. 97. We thus obtain 
a wavy line showing the rise 
and fall of temperature, and a 
line of this kind is called a tem- 
perature curve. 

Graphic Plan of showing Rise 
or Fall of the Barometer.— The 
plan by which the readings of a thermometer can be shown 



do 
80 

70 
60 
50 
40 
30 
20 
10 






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\ t 2 3 ^ 5 6 7 \ 



Fig. 97.— The zig-zag line repre- 
sents the rise and fall of tempera- 
ture during seven days. It is 
called a temperature curve. 



GRAPHIC REPRESENTATION. 



141 



MON. 28. 


TUE. ». 


•WED. 30. 


THU. 1. 


a 
3 

1 


N.W. 


N. 


S.W. 


S. 


5 

30 
5 

2$ 
5 






6 

30 
5 

29 
5 


— 




5 

30 
6 

29 
5 


— 




5 

30 

S 

29 

6 


— 




— 







— 




-^ 


^ 


^= 


^ 




^.^ 



Fig. 98.— The Daily News weather chart. The 
thick upright lines represent the top part of the 
mercury in a barometer. 



graphically is also used to exhibit the readings of a barometer, 
and it is adopted in many newspapers. The thick upright lines 
in Fig. 98 represent the mercury near the top of a barometer, as 
shown by the Daily News. The numbers 29 and 30 at the side 
of these lines mean 
inches, and the di\i- 
sions between the num- 
bers are tenths of 
inches. The height 
of the mercur)^ upon 
the dates marked upon 
the chart can thus be 
seen at once. The 
dotted lines indicate 
the highest and lowest 
readings of the baro- 
meter observed upon 
each of the days re- 
ferred to. 

Now look at Fig. 99, 
which shows the Daily Chronicle charts for the same days as 
the Daily News. There are no thick upright lines in the Daily 
Chronicle's charts, but the position of the top of the mercury is 

shown by a thick line 
running across the 
chart. This line shows 
very clearly how the 
mercury rose and fell 
on the four days in- 
cluded in the charts. 
The barometer is ob- 
served at the Daily 
Chronicle office four 
times a day instead of 
once a day, so the 
diagram differs a little 
from that of the Daily 
News. The thin line 
shows how the temperature varied on the same days, the 



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WEDS'ESDAY \ THORSDAY 


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Fig. 99. — The Daily Chronicle weather chart for 
the same days as in Fig. 08. The thick wavy line 
represents how the top of the mercury in a baro- 
meter varied in height during four successive days. 



142 ELEMENTARY PHYSICS AND CHEMISTRY. 

numbers which refer to temperatures being printed at the 
right side of the chart. 

To BE Remembered. 

It is sometimes more useful to represent quantities by the length of 
lines than by numbers. 

Comparison is made easier by this means. 

This and similar methods are known as graphic representation. 

Graphic representation is very convenient for recording readings of 
the barometer and thermometer. 

Exercise XXXIV. 

1 . Can quantities be represented in any other way than by numbers ? 

2. Give a description of how to represent relative densities or volumes 
graphically. 

3. What do you understand by a temperature curve ? 

4. How is squared paper used to record temperatures and pressures ? 

5. Make a sketch of a temperature curve, marking the divisions 
necessary to understand it. 



LESSON XXXV. 

GRAPHIC REPRESENTATION— Continued. 
PRACTICAL WORK. 

Things required. — Squared paper, or chequer drawing book 
such as is used for Kindergarten drawing. Ruler and pencil. 
What to do. 

Using squared paper, practise representing graphically 
by making diagrams for the following cases : 

I. The number of 3rd class passengers by a certain popular 
train throughout a week : 

Passengers. Passengers. 



Monday, 


- 250 


Thursday, - 


- 220 


Tuesday, 


- 215 


Friday, 


- .85 


Wednesday, 


190 


Saturday, 


- 235 



GRAPHIC REPRESENTATION. 



143 



2. The number of visitors to an exhibition throughout a 
fortnight. Suppose the returns to be as follows : 







No 


. of Visitors. 






No. of Visitor 


Ia> 


' 2, - 


- 


10,500 


May 


9, - 


■ 9,650 




3, - 


- 


10,100 




10, - 


- 9,700 




4, - 


- 


9.850 




II, - 


- 8,340 




Si - 


- 


10,200 




12, - 


• 9,870 




6, - 


- 


9,900 




13, - 


- 6,520 




7, - 


- 


12,500 




14, - 


- 9,970 



In this exercise mark the days of the month at the bottom of 
the vertical lines. Let the bottom horizontal line represent 
6000, the tenth horizontal line 7000, and so on up to 11,000. 

3. The amounts of the collection in pence at a church on 
every .Sunday throughout a quarter : 





£ s. 


D. 




£ S. D. 


1st Sunday, 


6 7 


5 


7th 


Sunday, 6 211 


2nd „ 


7 10 


3 


8th 


5 18 I 


3rd „ 


5 5 


9 


9th 


7 17 


4th „ 


6 13 


7 


loth 


812 


5th „ 


7 5 


4 


nth 


923 


6th 


8 9 





I2th 


13 I 8 



All the amounts should be reduced to pence before com- 
mencing this exercise. 



REASONS AND RESULTS. 

Cases in which Graphic Representation is useful. — Graphic 
representation can be usefully employed in very many other 
cases besides those named in the last lesson. In fact, it is the 
most satisfactory' way of representing any two quantities which 
vary together. A graphic diagram can thus be constructed 
from the record of a cricketer's scores during a season's batting. 
Let us suppose that some particular batsman plays his first 
match on Saturday, May 13th, and that he is fortunate enough 



144 ELEMENTARY PHYSICS AND CHEMISTRY. 

to get an innings every Saturday until ttie end of August, and 
that he makes the following scores : 



May 



June 







Score. 


13, 


- 


- 10 


20, 


- 


- 15 


27, 


- 


- 5 


J, 


- 


- 23 


10, 


- 





17, 


- 


2 


24, 


- 


- 9 



July 



August 





Score. 


I, 


- 16 


8, - 


- 5 


15, - 


- II 


22, - 


- 30 


29, - 





5, - 


- 17 


12, - 


- 5 


19, - 


- 19 


26, - 


- 4 



He could make a graphic representation of his scores as in 
the illustration, in which the marks at the left-hand ends of 



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i3 50 J/ 3 10 i-j lA. 1 e If 2i SJ f li i() 1 

MAY JUNE JULY AUGUST 


1 




DATES b'F INNINGS 





Fig. 100. — A graphic diagram of a cricketer's score on different dates. 

the horizontal lines represent scores, and those at the bottom 
of the vertical lines stand for the dates of innings. 

Other Graphic Diagrams. — It is often very convenient and 
instructive to construct diagrams similar to those already ex- 
plained, to show at a glance how prices have varied from time 
to time. The diagram here shown, for instance (Fig. loi), re- 
presents clearly how the price of india-rubber has altered from 
year to year since 1877. The years are numbered at the top 
of the diagram. In the vertical column for every year is a dot 
to show the price of india-rubber per pound in that year. The 
prices are printed at the left hand ends of the horizontal lines. 
Beginning with 1877 it will be seen that the price per pound 



GRAPHIC KErKESENTATION. 



145 



was then between 2'i and 2/3. In 1878 the price was i/ii per 
pound, in 1879 between 2/7 and 2/9, and so on for other years. 
The diagram shows at once that india-rubber was cheapest in 



PHlCt 


YEARS. 1 


W7 


«78 


r879 


1880 


1881 


1682 


1881 


188* 


esi 


1886 


1887 


i88B|iae9 


1890 


I89J 


1892 


18931894 


1895 


1896 


1897 


,C3.| 


— 


— 


— 






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Fig. ioi. — To show how the price of india-rubber per lb. rose and fell 
between 1877 and 1898. (From the Keiv Bulletirt.) 



1878, for the price per pound was then at the lowest point. 

The highest price was obtained in 1883 and 1898. Diagrams 

of this kind can be used to represent graphically the rise and 

fall in price of anything. A rise of the line shows a rise in 

price, and a fall shows a fall in price. 

Solubility Curves. — An interesting and important application 

of graphic representation is to show easily how the solubility of 

a soHd in a liquid varies with the temperature. Thus, Fig. 102 

shows the number of grams of the three solids, nitre, common 

salt, and chlorate of potash, which will dissolve in 100 grams 

of water at different temperatures. The degrees on a Centigrade 

thermometer are marked along the bottom horizontal line, and 

the length of the side of one square represents five degrees. 

The number of grams of solid which the 100 grams of water 

contain is read off from the scale on the left-hand of the 

diagram. The length of the side of one square represents 

five grams of dissolved solid. Thus, a reference to Fig. 102 

shows that 100 grams of water dissolve at 0° C. \i\ grams 

of nitre. 

I. K 



146 



ELEMENTARY PHYSICS AND CHEMISTRY. 



At 5° C. 100 grams of water dissolve 1 5 grams of nitre. 

10° C. „ „ 20 

15° C. „ „ 25 

20° C. „ „ 32 

25° C. „ „ 37i 

30° C- » » 45 

35° C. „ „ 55 

40° C. „ „ 64 

45° C. „ „ 75 

50° C. „ „ 87* 

55° C. „ „ 100 

We could read off the amounts of common salt and chlorate 

of potash dissolved in 100 grams of water at different tem- 
peratures in just the same manner. 



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30° 40'* So" 60° 7cr bo" 90° 100°C 
^ DEGREES OF TEMPERATURE. 

Fig. 102. — The number of grams of nitre, common salt, and chlorate 
of potash which can be dissolved in loo grams of water at any tempera- 
ture from 0° to 100° C. is shown in this diagram. 



But when we have several solubility cur\^es together in this 
way, we can very easily compare the solubility of the different 
solids together. We see, for instance, that the amourtt of nitre 
which will dissolve in 100 grams of water increases very rapidly 



GRAPHIC REPRESENTATION. 



147 



as the temperature rises, as the steepness of this particular 
curve shows. The amount of common salt which 100 grams 
of water will dissolve increases very little as the temperature 
rises. The curve is almost a horizontal line, for while at 
0° C. about 36 grams are dissolved by 100 grams of water, at 
100° C. the amount in solution is only 38 grams. 

To BE Remembered. 

Graphic representation is very convenient wherever we have two 
sets of quantities varying together. 

Solubility curves show the amounts of solids which will dissolve in 
liquids at different temperatures. 



Exercise XXXV. 

1. How could a cricketer represent his scores for a whole season 
graphically ? 

2. Explain how graphic representation is useful in recording regular 
variations in the price of any article. 

3. What is a solubility curve ? Draw the solubility curve for nitre 
and common salt. 

4. A boy counted his marbles every night for ten days, and found 
he {Kjssessed the following numbers : 



Jays. 


Marbles 


I 


50 


2 


65 


3 


78 


4 


49 


5 


43 



Days. 


Marbles 


6 


36 


7 


24 


8 


43 


9 


59 


10 


71 



Try to represent these numbers on a piece of squared paper. 

5. Represent by a diagram the following number of horse chestnuts 
which a boy possessed during the first fortnight of October : 
Date. 
Oct. 





Chestnuts 


I 


7 


2 


25 


3 


40 


4 


76 


5 


130 


6 


151 


7 


•97 



Date. 


Chestnuts 


Oct. 8 


142 


„ 9 


127 


,, ID 


109 


■,, II 


97 


5> 12 


54 


M 13 


19 


,. 14 


* 



INDEX. 



Air, around us, 71-75 ; has mass, 
74 ; exerts pressure, tj ; presses 
in all directions, 77 ; dissolved in 
water, 109. 

Amorphous, 17, 18. 

Archimedes, principle of, 64-68. 

Area, measurement of, 24. 

Balance, 44 ; principle of, 42-45 ; 

used for comparing masses, 45. 
Balloon, 67. 
Barometer, 79-83; definition of, 81; 

air pressure shown by, 81 ; when 

height of mercury in alters, 84 ; 

another form of, 84. 
Bellows, 78. 

Boiling point of water, loi. 
Brittle, 14. 
Buoyancy, 66. 

Camphor, 104. 

Cane, 17. 

Carbon bisulphide, 104. 

Centigrade thermometers, 100. 

Centimetre, 22. 

Chemical change, 113, 119. 

Combustible, 17, 19. 

Crystalline, 17, 18. 

Crystallisation of soda, 130. 

Crystals, 18, 125, and crystallisa- 
tion, 124 ; how made, 126 ; of 
alum, 126 ; of common salt, 130 ; 
of sulphur, 131. 



Cube, 125. 

Cubic measurements, 28, 30-32. 

Decanting, 108. 

Decimetre, 21. 

Decrepitation, 130. 

Dekametre, 22. 

Deliquescent, 126. 

Density, 46-49 ; meaning of, 47 ; 
high and low, 48 ; standard of, 
49 ; how measured, 51 : experi- 
mental determination of, 52 ; of 
solids, 69. 

Density bottle, 53. 

Diamond, 9. 

Dissolve, 17, 18. 

Efflorescent, 126. 

Elastic, 15. 

Elasticity, 15. 

Emery, 9. 

Evaporation, no- 114; a practical 

application of, 113. 
Expansion, 95. 

Fahrenheit thermometers, 100. 

Feeling, 2. 

Filter, 18. 

Filtering, 105. 

Fixed points, 98- 102 ; on a thermo- 

meter, 99. 
Flexible, 15. 
Foot, 21. 



148 



INDEX. 



I4Q 



Gases, 12; dissolved in liquids, 109. 

Glass, 14. 

Graduation of thermometers, 98-102. 

Gram, 39. 

Graphic representation, 133-147. 

Hardness, 7, 8 ; table of, 8. 
Hearing, 3. 

Height of barometer, 81. 
Hektometre, 22. 

Impervious, 17. 
Inch, 21. 

Incombustible, 17, 19. 
India-rubber, 15. 

Insoluble, 17, 18, and soluble solids, 
102-105 ; liquids, 108. 

Kilogram, 39. 
Kilometre, 22. 

Lactometer, 62. 
Lead, 14. 

Length, measurement of, 20. 
Liquids, 11. 
Litre, 31. 

Loss of vk^eight, of things in water, 
66. 

Malleable, 14. 

Mass and weight, 33-37 ; measure- 
ment of, 37-41 ; what mass is, 34; 
mass is not weight, 35 ; metric 
measurement of, 40. 

Matter, 6. 

Mercury, a convenient liquid for 
barometers, 85. 

Metre, 21 ; square, 26. 

Metric, 22, 26 ; masses, how to re- 
member, 40. 

Millimetre, 22. 

Octahedron, 125. 
Opaque, 14. 



Physical change, 112. 

Pint, 31. 

Pliable, 15. 

Porous, 16, 17. 

Pound, imperial standard pound 

avoirdupois, 39. 
Pressure of air, how measured, 80 ; 

at different altitudes, 86. 

Residue, 112. 
Rock-crystal, 125. 

Salt, 18. 

Saturated solution, 114-116. 

Science, how studied, i. 

Seeing, 2. 

See-saw, 43. 

Senses, 1-5 ; five, 4. 

Size, change of, 90. 

Smelling, 3. 

.Soda crystals, 128, 129. 

Soda-water, 109. 

Solids, II. 

Solubility curves, 145. 

.Solubility of things in acids, 116- 119. 

Soluble, 17, 19, and insoluble solids, 
102-105. 

Solution, 104 ; of liquids, 108 ; 
another kind of, 118. 

Solvent, water as a, 115. 

Sponge, 17. 

Spring balance, 35. 

Square measure, 26. 

State, change of, 91. 

Substances, 6 ; soluble, 104 ; in- 
soluble, 104; in suspension, 105. 

Sucker, 78. 

Sugar, 18. 

Tasting, 3. 

Temperature, change of, 91. 
Thermometer, 92, 93- 97 ; marks on, 
96. 



I50 



INDEX. 



Things, 6; many kinds of, 7 ; differ, 

7- 
Transparent, 14. 

U-tube, 55, 80. 

Varnish, 104. 

Volume, measurement of, 29 ; metric 

measure of, 30. 
Volume, of water displaced, 57 ; of 

an irregular solid, 58. 



Washing-soda, 128. 

Vv^ater, displaced by solids which 

float, 61; as a solvent, 115; of 

crystallisation, 126. 
Water-dust, 90. 
Weather glass, 82. 
Weather records, 138. 
Weight, 36 ; avoirdupois, 39. 
Weight of air, vk'hy not felt, 78. 

Yard, 21. 



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