ACID BASE EQUILIBRIUM: see DIET AND DIETETICS. ACIDIMETRY, the determination of the quantity of free acid (q.v.) in a substance. There are several methods of estima tion, one of the chief being by volumetric analysis (q.v.). A con venient method for the aqueous solution of a fairly pure acid is the determination of its specific gravity by means of a hydrometer (q.v.). (See CHEMISTRY : Analytical.)