OLEIC ACID. As oleate of glycerin, or olein, this acid forms the greater portion of all drying oils and the fluid part of nearly all fats.
Olein or claim It was first observed by Chevreul that expressed oils and kinds of fat usually contain two oils of different degrees of fusibility, or in other words, two different fatty substances ; so that on cooling any expressed oil, one part of it became solid, while another portion retained its fluidity. In consequence of this observation he concluded that all expressed oils are similarly con stituted ; to the less fusible one gave the name of stearin (from crrlap, suet), and the more fusible lie termed elain (from lamer, oil), which was afterwards changed to olein.
Several methods have been proposed for separating these two sub stances. When olive oil, for example, is exposed to a low temperature, a portion of it becomes solid, and the remainder retains its fluid form; the former is stearin, or margarin, and the latter (kin; these are separated by absorbing the liquid part by blotting-paper, and pressing the solid portion between folds of this paper till it ceases to render it greasy. The olein which the paper has absorbed is then to be separated from it by boiling it in water, on which the olein floats, and the paper sinks.
Olein has scarcely any taste or smell when procured from oils which possess these properties only in a slight degree. Its specific gravity is 0.98, it solidifies at 27° Fahr., and crystallises in needles. In water it is quite insoluble, but alcohol takes it up largely when boiling ; by the alkalies potash and soda it is readily saponified, and during this operation oleic acid is fanned by a new arrangement of the elements of the olein and their action on the elements of water; and these changes occur without the evolution of any gaseous matter.
On account of the very low temperature at which olein con geals, it is well adapted for lubricating the wheels of watches, and its value in this respect is enhanced by its not readily becoming rancid by the action of the air.
Although olein is frequently regarded simply as terolente of glycerin, its constitution is more correctly expressed by regarding it as glycerin
.II "' ) 0„ in which three equivalents of hydrogen are replaced by three of the acid radical Berthclot has indeed succeeded in forming this compound (terolein) artificially, as well as diolein and monolein. The processes he adopted have already been described under GLYCLRIff ; the following formulro will however chow the relations the compounds in question bear to each other :— Elaiain is'a solid modification of olein, and is produced when the latter is subjected to the influence of peroxide of nitrogen. [ELerom.] Linolein is the name given to the olein of linseed oil; it contains linoleic acid differing apparently from oleic add, but requir ing farther investigation.
Oleic acid (HO, The preparation of this acid in the pure state is not an easy matter. Olein obtained in the manner above described still contains small quantities of margarin and stearin, and on saponification with an alkali yields margamte and stearate as well as oleate of the base. One of the best methods consists in saponifying with oxide of lead, digesting the resulting salts in ether for twenty four hours, whereby oleate of lead only is dissolved ; the oleic acid separated from the latter salt is super-saturated with ammonia, precipi tated by chloride of barium, the oleate of barytes dried and boiled with alcohol, and the crystalline': plates deposited on cooling finally decom posed by tartaric acid, when pure oleic acid separates.
Pure oleic acid is colourless, inodorous and tasteless. At about 40° Fahr. it solidifies into a hard white mass of acicular crystals, but at temperatures above 57° remains as a limpid oleaginous liquid, insol uble in water but soluble in alcohol or ether. It rapidly absorbs oxygen from the air, acquires a rancid smell and taste, tunes litmus paper red, and has its point of solidification gradually lowered to below the zero of Fahrenheit's scale. By beat oleic acid is broken up into several gaseous and liquid bodies ; among the latter is sebacic acid, a matter not obtained in the destructive distillation of the other oily acids.