Oleic Acid, an organic, monatomic acid, found in combination with glycerine in oils and fats, as oleine, or oleate of glycerine. It is obtained by the saponification of oleine, the most fluid constituent of the natural fats and fixed oils. Olive or almond oil is treated with potash, which sets free the glycerine, oleate of potash being formed in the soapy mixture. This soap is treated with tartaric acid, which combining with the potash forms tartrate of potash; and the separated fatty acid, after being washed, is heated for some hours in a water bath with half its weight of oxide of lead. The mixture is then shaken with twice its bulk of ether, which dissolves the oleate of lead and leaves the stearate. After standing some time the mixture is decanted and hydrochloric acid added to it; this unites with the lead and liberates the oleic acid, which dissolves in the ether and rises to the surface of the water, from which it is removed and freed from ether by distillation. Large quantities of crude oleic acid are now obtained in the manufacture of stearine candles, by treating with dilute sulphuric acid the lime soap produced by the action of lime upon tallow.

The fatty olEron acids which are thus liberated, being washed with hot water, solidify on cooling into a mass, which when subjected to pressure yields a liquid rich in oleic acid, but containing considerable stearic acid. After exposure to cold this liquid deposits a quantity of solid matter, and the remaining liquid portion is sent to market under the names of oleic acid and red oil, which may be purified by the processes above described. Oleic acid crystallizes from its alcoholic solution in dazzling white needles, melting at 57° F. to a colorless oil, which at 39° solidifies to a hard, white, crystalline mass, expanding considerably at the same time. Its specific gravity at 66° is 0.898. It vaporizes in a vacuum without decomposition; is insoluble in water, very soluble in alcohol, and dissolves in all proportions in ether. It dissolves the solid fats, and is dissolved by bile, forming a soap. It oxidizes but slowly when solid, but when melted it rapidly absorbs oxygen and becomes strongly rancid. With glycerine it forms three glycerides, monoleine, dioleine, and trioleine. With ammonia and the metallic bases it forms salts called oleates, the oleate of lead being used in purifying the acids.

The oleates of the alkalies are always formed in the manufacture of soap.