ELEMENTARY
PHYSICS AND CHEMISTRY

GREGORY AND SIMMONS

FIRST STAGE

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1905

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ELEMENTARY PHYSICS AND
CHEMISTRY

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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 ni 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.

19-

"

n

~

C^-r-k-f

:r

.

c^

i.'

>

►jpec

11

ii

-

tjlciy]^

Lit

:iS

16

13-

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

I

I J

I J

I

I

I J

I

,

.

y '

60

—

h-

\

1 Z 3 4- 5 6 7 \

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

^-

v^

,-'

'

\

y

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

/

\

>

y

f

\

\

^

\

y

\ 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

g

)iONDA r. 1 TVESDd Y.

WEDS'ESDAY \ THORSDAY

i

s

.*.'•-/. "-J."-,'.

,',,=0. ,'.»,..,'.«<-./.,

k

X

_J

1

—

^

1=

p— 1

^

—

50

zr

—

^

^

nd

\^'

"^

-

ZI

—

1 '

i^

1

—

— y

— '

— '

I)

^

.

/

1

1

'

.^

^^

__

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 0

4th „

6 13

7

loth

812

5th „

7 5

4

nth

923

6th

8 9

0

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,

-

0

17,

-

2

24,

-

- 9

July

August

Score.

I,

- 16

8, -

- 5

15, -

- II

22, -

- 30

29, -

0

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

t/J-

ZD

a: 30

CO '0

Is

j

1

;

/

\

1

/

\

t

\

1

\

\

1

/

\

/

1

\

1

\

\

-^

'

1

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.|

—

—

—

r"

Y

—

—

—

-^

—

—

— ^

-^

-

-

—

—

h

4-

—

—

-

-

-

-

7

-

/

J

,

,

,

-^

,

A

_

1

-t

/•

K

Z^

'

h

~P\

S

h — i

t-

s;

;z

—

—

-f

—

r^

^^

—

V

■v^

^—

1

1

.._^

,

/_

[1

,

2. 1
1 .11

-j

—

—

—

— '

H

—

—

■ —

J

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.

E'oo

1-

—

—

—

—

—

—

—

—

u.

i

0) 80

S

1

§ TO

0

2 60

z

>

f.^

/

Q K.n

/

^j

/

a -'O

r

*

/

8 *o

/

/

•t^

—

L—

Q

~

/

—

Co

m

vo

7-

b'a

t-

/

r

—

~

CO

/

Jr.^'

<

a 20
0

/

^

kr

/

-d

V

IL

0 10
a

\i^

^

-"5

lfiV>

Ul

(0 r.

<—

■""

"■

L.

L

L-

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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