Oleic Acid

Oleic Acid is one of the acids present in olive, almond, and other oils, in which it is united to glycerine. At temperatures above $57^\backslash circ$ ($14^\backslash circ$ C.) it exists as a colourless limpid fluid, of an oily consistency, devoid of smell and taste, and (if it has not been exposed to air) exerting no action on vegetable colours. At $40^\backslash circ$ ($4.4^\backslash circ$ C.) it solidifies into a firm, white, crystalline mass, and in this state it undergoes no change in the air; but when fluid it readily absorbs oxygen, becomes yellow and rancid, and exhibits a strong acid reaction with litmus paper. It is very difficult to obtain the acid in a state of purity, in consequence of the readiness with which it oxidises. It is obtained in a crude form, as a secondary product, in the manufacture of stearin candles; but when the pure acid is required a lengthy process, starting with almond oil, must be adopted. Oleic acid forms normal (or neutral) and acid salts; but the first compounds of this class that require notice are the normal salts of the alkalies. These are all soluble, and by the evaporation of their aqueous solution form soaps. Oleate of potash forms a soft soap, which is the chief ingredient in Naples soap; while oleate of soda is a hard soap, which enters largely into the composition of Marseilles soap. Of recent years a large number of oleates have come into use in medicine, which depend for their activity on the remarkable ease with which they are absorbed by the skin. Such are the oleates of zinc, mercury, lead, tin, morphia, &c., which, in this form, produce more rapid results than when applied as ointments.