II. Absorption of Gases by Solids and Liquids. There are not only porous substances, as earth, charcoal, and animal membranes, which will absorb gases, but solid metals will in many instances do the same. Thus recent experiments have demonstrated the existence of gaseous hydrogen in meteorites falling on the earth, absorbed by them in their wanderings through space, perhaps while passing through some nebula, which the spectroscope has shown to consist of incandescent hvdrogen; they bring thence this nebular hydrogen to our earth. The power to absorb hydrogen is especially possessed in a high degree by palladium, which takes up nearly 643 times its own volume of this gas, as proved by Graham, while silver and platinum absorb oxygen, titanium nitrogen, etc. This absorption of gas by metals is called occlusion. Deville and Troost have proved the remarkable fact that red-hot iron and platinum have such a great capacity of absorbing hydrogen, that it passes through these metals as it were through a sieve. The absorption of gases by liquids is still more striking. "Water absorbs different gases and holds them in solution, in quantities varying in proportion to the nature of the gas.

Thus, at a temperature of a few degrees above the freezing point, it contains when exposed to the air ' 4 per cent, in volume of oxygen and 2 per cent. of nitrogen; so that the air contained in water is much richer in oxygen than our atmosphere, having in six parts four of oxygen, while the atmosphere contains only one part of oxygen in five of air. The solubility of hydrogen in i water is equal to that of nitrogen; while in regard to other gases, one part of water in bulk dissolves under the same circumstances 1.3 parts of laughing gas, 1.8 carbonic acid, 3 of chlorine, 4.4 of sulphide of hydrogen. 54 of sulphurous acid, 505 of hydrochloric acid, and not less than 1,180 of ammonia. A rise of temperature of some 70° diminishes this power of absorption to about one half, while at the temperature of the boiling point of water most absorbed gases are expelled. With a diminished pressure of say half an atmosphere, about half the gas is expelled; while at an increased pressure of say two atmospheres, more gas can be absorbed.

Thus in respect of carbonic acid, for instance, every atmosphere pressure augments the capacity of water to absorb this gas by 1 .8 volumes, so that at five atmospheres it absorbs nine times its own volume of the same.

The absorption of gases by other liquids than water is a subject still open for investigation, and has thus far only been determined for a few gases. So Dr. Vander Weyde of New York found in regard to laughing gas, that alkaline solutions absorb more than pure water, and alcoholic liquors most, strong alcohol over five times its volume; solutions of neutral salts in general absorb the same amount as water, except the sulphates, which absorb much less of the gas, while acids absorb the least, especially diluted sulphuric acid, which absorbs only 0.3 to 0.05 of its volume, according to its strength.