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What Gases Are

The behaviour of a gas is easily enough understood if we remember what it is. A gas is a very scattered assembly of molecules moving as fast as bullets but not getting very far before they collide with each other. Each molecule has a good big free space round it: in fact, a molecule of a gas has about a thousand times as much elbow-room as a molecule of a liquid or a solid. Well, anyone can see that if this is a true picture of a gas, it must be very light, because it is made up of very few molecules. Picture a swarm of midges in which each midge was about two inches from the next and you will have a fair notion of the amount of elbow-room in a gas. It follows from that a gas will flow very easily, for the molecules will not get in each other's way, nor will they greatly attract or repel each other. For the latter reason, it should be easy to compress a gas: a solid or liquid is almost incompressible because the repulsions of the electrical charges of which its atoms are made up are far stronger than any forces we can apply. In the case of a gas, the molecules are much too far from each other to repel each other. Of course, the idea of a gas as a swarm of busy molecules is not much more than a hundred years old. Gases are so unlike any other kind of matter that many centuries elapsed before people made up their minds that they were matter at all.

One of the reasons why people before the eighteenth century knew hardly anything about gases was that they are difficult to handle. You can put a solid in a basket or a basin, you can pour a liquid into a jug, but a gas has to be handled in a special way. Suppose you have a bottle full of it. As soon as you uncork it, the gas molecules begin to spread into the air and the air molecules into the gas [2, С. 69].

Have you ever bought gases? Are you sure? Read the text, translate it and, however, say what gases you happened to buy and for what purposes.

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