The Romance of Modern Chemistry

INVISIBLE SUBSTANCES Once again—all solid and liquid substances with which we are familiar are characterised as light or heavy—in other words, they have weight. In this respect also air and other gases conform to what is commonly character- istic of all material bodies. It is true that, bulk for bulk, gases weigh much less than water, or wood, or stone, but the difference is only one of degree. One simple way of showing that air has weight is to put a little water in a glass flask, and let it boil vigorously until the flask is fall of steam. It is then corked tightly and removed at once from the source of heat. When the flask and its contents have become quite cold, they are put on one side of a sensitive balance, sufficient weights being put on the other side to keep it level. The cork is then removed for a moment, and it will be observed that the side of the balance on which the flask was placed goes down at once, showing that the mere opening of the flask causes it to become heavier. What has happened is that the steam which filled the flask when it was hot became condensed to water when the flask had cooled, thereby leaving room for air to enter as soon as the cork was removed. It is the entrance of this invisible some- thing from the surrounding atmosphere which makes the flask heavier. Gases, then, have weight, and are on this ground also to be reckoned as material substances. As has been said already, gases are very light com- pared with other substances; they are matter in a very attenuated form. A pint of water is nearly 800 times as heavy as a pint of air, and with the gas hydrogen the contrast is still more marked. For air is fourteen and a half times as heavy as hydrogen, so that a pint of water weighs 11,500 times as much as a pint of hydrogen. It may truly be said that a pint of hydrogen is as light as 41