All gases are more or less soluble in water and other liquids. Some gases, as, for example, hydrochloric acid and ammonia, arc absorbed by water very rapidly, and to a great extent, the liquid taking up 400 or 600 times its bulk of the gas; in other cases, as carbonic acid, water takes up its own volume of the gas; whilst in the case of nitro gen, oxygen, and hydrogen, it does not take up more than from A to Bs of its bulk.
As the elasticity of the gas," says prof. Miller, " is the power which is here opposed to adhesion, and which at length limits the quantity dissolved, it is found that the solu bility of each gas is greater, the lower the temperature, and the greater the pressure exerted upon the surface of the liquid. Dr. Henry found that at any given tempera ture the votunie of any gas which was absorbed was uniform, whatever might be the pressure; consequently, that the weight of any given gas absorbed by a given volume of any liquid at a fixed temperature, increased directly with the pressure. If the pressure be uniform, the quantity of any given gas absorbed by a given liquid is also uniform for each temperature; and the numerical expression of the solubility of each gas in such liquids, is termed its coefficient of absorption or of solubility, at the particular tem perature and pressure, the volume of the gas absorbed 'tieing in all cases calculated for 32° F., under a pressure of 29.92 in. of mercury. Thus, 1 volume of water at 32°, and tinder a pressure of 29.92 in, of the barometer, dissolves 0.04114 of its of oxygen; and this fraction represents the' coefficient of absorption of oxygen at that and pressure. Similarly, the coefficient of absorption of common air is 0.02471. In consequence of this solubility of the air, all water contains a certain small proportion of it in solution; and if placed in is vessel under the air•piunp, so as to remove the atmospheric pressure from its surface, the dissolved gases rise in minute bubbles. Small as is the quantity of oxygen thus taken up by water from the atmos phere, it is the means of maintaining the life of all aquatic animals. If the air be expelled from water by boiling, and it be covered with a layer of oil, to prevent it from again absorbing air, fish or any aquatic animals placed in such water quickly perish. Even the life of the superior animals is dependent upon the of oxygen in the fluid which moistens the air-tubes of the lungs. in consequence of which this gas is absorbed into the mass of the blood, and circulation through .the pulmonary vessels." All these gases, with the exception of hydrochloric acid, may be expelled from the water by long-continued boiling.
Gases are not absorbed by all liquids in the same order; for example, naphtha absorbs most olefiaut gas, oil of lavender most protOxide of nitrogen, olive oil most carbonic acid, and solution of chloride of potassium most carbonic oxide, If a mixture of two or more gases be agitated with water, or probably any other liquid, a portion of each gas will be absorbed, and the amount of each so absorbed or dissolved will be proportional to the relative volume of each gas multiplied with its coefficient of solubility at the observed temperature and pressure. As all ordinary liquids exert a greater or less solvent action on gases, a gas that we wish to examine quantitatively should be collected over mercury.
The adhesion of gases to solids next requires notice. Illustrations of this phenome non perpetually occur. Thus, wood and other solid substances immersed in water or other liquids appear covered with air-bubbles. It is this adhesion of air to the surface of glass tubes which causes the difficulty of obtaining barometers and thermometers completely free from air. It is in consequence of the adhesion of air to their surfaces that many small insects are enabled to skim lightly over the surface of water which does not wet them. A simple method of illustrating this phenomenon is by gently dusting iron filings over the surface of a vessel of water; if we proceed carefully, a con siderable mass of the iron may accumulate upon the surface; till, at last. it falls in large flakes, carrying down with it numerous bubbles of air. As the particles of iron are nearly eight times as heavy as water; it was only the adherent air that enabled them to float upon the surface. Closely allied to this adhesion is the remarkable property of condensation which porous bodies, and especially charcoal, exert on gases. Owing to this property of charcoal—especially freshly burned vegetable charcoal—various gases may be separated from their watery solution by filtration of the latter through it; for example, sulphureted hydrogen may be removed from water so completely that it can not be detected either by its well-known odor or by the ordinary tests. Saussure found that 1 volume of freshly burned box-wood charcoal absorbed 90 volumes of ammonia, 85 of hydrochloric acid, 65 of sulphurous acid, 55 of sulphureted hydrogen, 40 of pro toxide of nitrogen, 35 of carbonic acid, 35 of hicarbureted hydrogen, 9.4 of carbonic oxide, 9.2 of oxygen, 7.5 of nitrogen, 5.0 of carbureted hydrogen, and 1.7 of hydrogen. These results follow an order very nearly the same as that of the solubility of the gases in water.