SOLUTION

a homogeneous mixture of substances that cannot be separated by mechanical means. In the wider sense the term includes gases and solids as well as liquids. Gaseous Soluttons—Gases that do not interact chemically mix in all proportions by agitation or diffusion. The total pre ure of a mixture of gases is the sum of the partial pre ures of the constituents. Liquids di olve in gases by evaporation, solids by sublimation. Liquid Solutions —Some liquids—_ (e.g.) alcohol and water—mix in all proporti ons; otherwise solution in liquids is limited in extent. The liquid receiving a substance into solution is called the solvent; the di olved substance is the solute. The amount of solute which will di olve in a fixed amount of solvent is its solubility; the degree of solubility depends partly on physical conditions. A solution is saturated when its concentration will remain constant in contact with the solute, (1) Solutions of Gases in Liquids.— The solubilities of different gases differ greatly; they vary with different liquids and diminish with rising temp., till at the boiling-points of liquids they are zero; and the quantity of a gas which will di olve in a given quantity ofa liquid— (e.g.) Water, at a given temp.—is proportion al to the pre ure of the gas; its volume is indepen dent of the pre ure. The volume of a gas which will di olve in unit volume of a liquid at 0° CG. is its absorption coefficient. The relative quantities of the constituents of a gaseous mixture (e.g., air) which will di olve in water thus depend on their absorption of coefficients and their partial pre ures. (2) Solutions of Solids in Liquids.— Different solids di olve in liquids to widely different extents. The solubility of a solid in a liquid thus depends on the nature of the solid and of the liquid, as well as upon the latter’s temp. For inorganic salts water is the usual solvent; for many carbon compounds alcohol, ether, benzene, etc., are better. The solubilities of solids are conveniently expre ed in grammes per 100 grammes of solvent. Solubility generally increases with temp.; consequently a _ solution saturated at a given temp. may be made, not only by agitating the solid with the liquid at that temp., but by heating it with the liquid to a higher temp., and allowing the solution to cool to the required temp. in contact with the solid. If a hot saturated solution cools in entire absence of the solid, separation of the latter may not take place, the solution remaining supersaturated. If, then, a fragment of solid is added, rapid separation occurs till equilibrium be. tween solution and solid results, Solutions of substances may or may ynot conduct an electric current. Aqueous solutions of acids, bases, and salts conduct while they undergo electrolysis; they are electrolytes. Solutions of other substances are non-conductors, and nonelectrolytes. Solid Solutions are formed (1) by the simultaneous separation of two or more solids from a liquid solution— (e.g.) mixed crystals; (2) by the solidification of a liquid solution—(e.g.) alloys, gla es, cryohydrates. See also EizcTRICITY.