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THE THREE STATES OF MATTER
STONE, a piece of wood, a bar of iron, are objects more
or less hard which offer resistance to the finger and
can be grasped and handled. Cut or chiseled into any
desired shape, they will retain that shape. On account
of these properties we say of stone, wood, iron, and
other substances that resemble them in this regard,
that they are solid substances."
"In everyday language this term 'solid' is applied to
any object that offers great resistance to rupture, to
deformation. For example, we say 'This piece of wood
is solid,' 'This iron hook is very sold.' That is not
the way the word should be understood in the present
connection. I call solid any substance that can be
grasped and handled, any substance, in short, that
keeps the shape given it. Thus butter, tallow, moist
clay, are plastic substances readily molded by the hand
into any desired shape. We can grasp and handle them
without difficulty, can fashion them as we please. In
this sense they are solid substances no less than
marble and iron, which are so resistant."
"That is easy to understand," said Claire. "Anything
that can be handled, even if softer than butter, is
called solid. So water is not solid, for I can't
 take up a pinch of it in my fingers as I do with sand.
Neither can I shape some of it in the form of a
nine-pin, for example, and stand it up; or at least I
can't unless I put it in a bottle."
"Golden-tongue could not have said it better. No,
water is not solid. It slips through the hand that
tries to hold it; it flows. Left to itself it has no
shape, and it is impossible to give it a definite one
except by enclosing it in a vessel. Then it adapts
itself to the form of the container, taking its exact
shape—round if the vessel is round, cubical if
the vessel is a cube. Water and other substances that
flow are called liquids."
"Then milk, oil, wine, vinegar, melted butter, are all
liquids," said Jules.
"Yes, they are liquids the same as water.
"Now let us turn our attention to the steam that
escapes from a boiling pot or, if you like, to the
beautiful plume of white vapor that comes in puffs from
the smoke-stack of a locomotive as the latter moves
along on the iron rails. You remember those
magnificent puffs ascending in billows that remind one
of the softest kind of swans' down."
"I know what you mean," Emile hastened to reply; "the
engine puffs them out with a loud noise like a person
blowing with all his might."
"Well, those white puffs are steam from water, just
like the white puffs from the little boiling pot. This
steam makes the locomotive move, and then, after it has
done its work, it escapes with a loud noise into the
air. Here we have another substance impossible to
grasp; and this impossibility is greater
 even than in the case of water. Handling it is quite
out of the question. Moreover, it expands in all
directions, gaining in volume and occupying an
increasing amount of space. On issuing from the
smoke-stack the puff of steam had a certain volume, not
very large. Inside the engine it had still less, and
that is precisely what gave it its force; for, like a
spring that possesses more energy the more it is
pressed down, steam owes its power to the fact of its
confinement within a restricted space. Once set free,
it gains more and more volume until at last it becomes
so dispersed as to be invisible. You must, in fact,
have noticed that the white plume soon melts, as it
were, in the air and disappears.
"Invisible though it thus becomes, it is clear that
this steam exists and that it belongs to a special
class of material substances. Is not hair itself
intangible and invisible? And yet can one doubt its
materiality when, as wind, it is set in violent motion
and makes the trees rock and sway, or even tears them
up by the roots? Thus we perceive there are substances
characterized by an extreme thinness, the thinness of
the air we breathe. These substances do not retain any
fixed form like solids; they have no constant volume
like liquids; they expand in all directions and, unless
confined, occupy more and more space. They are called
aëriform substances on account of their
resemblance to air; they are also known as gases and
vapors. Air is a gas. To this class belong also the
invisible but pungent fumes of burning sulphur, and the
greenish substance of unbearable smell whose properties
I described to you in our talks on coloring
 matter and on ink in particular. The first-named
substance is sulphurous oxide, useful in bleaching wool
and silk; the other is chlorine. Lastly, the invisible
steam from boiling water is also a kind of gas, or
rather a vapor, for as and vapor are much alike."
"And that kind of air full of something that comes from
burning charcoal, that dangerous air that gives ironers
a headache if they are not careful to keep their
heaters under a chimneythat must be a gas too?"
This query came from Claire.
"The deadly substance emitted by burning charcoal is in
truth a gas, as invisible and as odorless as air
itself. It is called carbonic oxide.
"Thus all substances, or, to use another term, all
bodies, assume one or other of the three different
forms known as the three states of matter; namely,
solid, liquid, and gaseous.
"Now the same substance can, without changing its
nature in the least, become in turn solid, liquid, and
gaseous, according to circumstances. It is mainly heat
that effects these transformations. Heated to the
requisite temperature, certain solids become liquid;
with still more heat the liquid becomes a gas. In
losing heat, on the other hand, that is to say in
cooling, a gaseous body passes successively from the
gaseous to the liquid state, and from that to the
solid. The following example will show this more
clearly than any mere description.
"Ice is a solid body; many stones are no harder. Let
us put it on the fire in a vessel. It will melt; in
gaining heat it will become liquid water. If this
water in its turn is heated still more, it will begin
 boil and will pass of in vapor; that is to say, it will
take the gaseous state. Here, then, we can see water
changing, under the action of heat, from the solid to
the liquid state, and from the liquid to the gaseous.
Most bodies are subject to similar changes. It is true
that sometimes heat of extreme violence is needed, thus
iron will not melt unless subjected to the intense heat
of the blast-furnace; and to vaporize the smallest
particle of it requires the most tremendous sort of
fire that science can produce. And so with varying
degrees of reluctance all elemental substances obey
this common law: heat first melts them, makes them
become liquid, then volatilizes them, that is to say
reduces them to vapor.
"What does cold do on its part? First take notice that
cold has no real existence, that it is not something
opposed to heat. All bodies without exception contain
heat, some more, some less, and we call them hot or
cold according to whether they are warmer or colder
than we. Thus heat is everywhere, and cold is only a
word that serves to designate the lesser degrees of
heat. To cool a body is not to add cold to it, there
being no such thing as cold; it is taking heat away.
If a body gains heat it becomes warm; if it loses heat
it turns cold.
"Well, then, the act of cooling, that is to say the
withdrawal of heat, restores vaporous bodies to the
liquid state, and liquids to the solid state. Thus the
steam from the boiling pot on coming in contact with
the cold lid loses its heat and turns to water again;
and the vapor in our breath, when it touches a pane of
glass, becomes cold and runs down in fine drops.
 Water in its turn sufficiently cooled turns to ice,
that is to say becomes solid. Other substances act in
the same way: a diminution of heat brings them back
from the gaseous to the liquid state, then from the
liquid to the solid."