The Three States of Matter

"A 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 solid.' 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 air 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 gas 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 chimney—that 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 to boil and will pass off 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."