Precipitation

(pre-sip-it-a' -shun). The proce of throwing down solids from the liquids which hold them in solution. It is usually effected by iiemic reaction. Precipitates are crystalline, amorurdy, ftocculent, granular, or gelatinous, according to the form a umed. The agent causing precipitation is the precipitant, the solid thrown down, the precipitate. P., Fractional, the proce employed in separating a mixture of fatty acids by the addition of small portions of the acetate of a heavy metal. The precipitate consists of a combination of the metal with a large proportion of the le volatile acid and a small proportion of the more volatile acid. In the filtrate the proportions are reversed. The metal is separated from the le volatile acid by di olving the precipitate in hydrochloric acid. The proce is repeated until finally the filtrate contains practically only the more volatile acid, and the precipitate only the le volatile acid. P., Partial, a proce of separating two soluble salts by precipitation of a portion of each, and subsequent decomposition of the precipitate. The latter is redi olved and again precipitated.