LIQUID SOLUTIONS. These may be formed by liquids with gases, by liquids with other liquids, and by liquids with solids.
The mass of any gas absorbed by any liquid is proportional to the pressure of the gas (Henry's law) and diminishes with increasing temperature. Of course, even under the same conditions of pressure and temperature the solu bility of different gases in some liquid is not the same: thus carbonic acid gas is much more soluble in water than oxygen. The solubility in the ease of each system consisting of a gas and a liquid is termed by Bunsen the 'coefficient of absorption.' To understand clearly the meaning of this term imagine some gas in contact with a given liquid and maintained at some tempera ture t, under a pressure equal to the normal pressure of the atmosphere; imagine that when no more of the gas is being absorbed, all the gas contained in one cubic centimeter of the solution is driven out of it, confined separately, and cooled off to 0° Cent.; the volume that the gas will then occupy is its coefficient of absorption with re spect to the given liquid at the temperature f. In the case of gases (such as ammonia, with respect to water) that are copiously soluble. i.e. whose coefficient of absorption is very large, that coefficient itself is variable, not only with the temperature, but also with the pressure of the gas; in other words, such gases fail to obey henry's law—probably because they enter, to a greater or less extent, into chemical combina tion with the solvent liquid. Why the coefficient of absorption should be exactly what it is. whether Henry's law is obeyed or not. is not yet understood. Nor do we understand clearly the state of a gas when absorbed by a liquid. Are its molecules combined with those of the solvent in the form of hydrates, or (In they exist in the solvent independently? On the other hand, it has been demonstrated that if a gas obeys Henry's law its molecules in solution are neither dissociated into simpled molecules nor associated with one another. It has also been shown that dilute solutions of gases in liquids obey the laws of osmotic pressure as well as do dilute solutions iu general (see' fur ther below).
Passing now to solution of liquids in liquids, we find, first of all, that some liquids (e.g. water and alcohol) are miscible in all propor tions, that the mutual solubility of others (e.g. water and ether) is limited, and that still others are practically insoluble in each other. There are strong reasons for assuming that the third of these classes is really identical with the sec ond; only the amounts dissolved are so small that they cannot be detected by the analytical means at our disposal. One of the most im portant properties of solutions of liquids in liquids is their vapor-tension, which plays an important part in processes of fractional dis tillation. (See DISTILLATION.) When two liq uids, A and B, are mixed, the vapor-tension of either undergoes a diminution: A in the solution is less volatile than in the free state, and so is B. The vapor-tension of each in the solution is termed its 'partial vapor-tension,' and the total vapor-tension of the solution is equal to the sum of the diminished, partial vapor-tensions of its ingredients. If A and B are mutually soluble to a limited extent, two solutions may be formed (viz. A in B and 13 in A). of which the partial as well as the total vapor-tensions are respective ly equal. Take, for instance, water and ether; if shaken up in sufficient relative quantities and then allowed to stand undisturbed they will form two distinct liquid layers, the upper a satu rated solution of water in ether, the lower a saturated solution of ether in water; the partial vapor-tension of the water in the upper equals the partial vapor-tension of the water in the lower solution : the partial vapor-tension of the ether in the upper equals the partial vapor-ten sion of the ether in the lower solution; and hence, the total vapor-tension of the upper solu tion equals the total vapor-tension of the lower. Analogous relations are found in all cases ex amined.