OILS (OF. oily, ole, vile, Fr. hui/c, from Lat. (ileum, oil, from Gk. aamv, cla(on, oil, olive oil, from i2eia, elaia, olive tree). A term applied to a large number of liquids characterized by being insoluble in water and being highly viscous. Their 'greasy feeling' often mentioned as an additional characteristic is due largely to their viscosity and insolubility in water. Capa bility of saponification (see further below), for merly considered essential, is confined to a variety of substances, chiefly of animal or vegetable origin, while the unsaponifiable class includes the so-called mineral oils and similar products pre pared artificially. Chemically the oils possess no property in common which would justify their being grouped together in any rational classifica tion of substances. And if they are still referred to collectively as a distinct class of chemical substances, it is owing partly to custom, partly to the fact that chemically different oils are sometimes associated industrially.
Liorm FATS. The vegetable and animal oils of liquid fats do not differ essentially from the class of substances described under FATS. They, too, contain olein, palmitin, and stearin, to gether with certain other fatty bodies, which give each oil its characteristic properties. Palm itin and stearin are solids at ordinary tempera tune, but are freely soluble in the liquid olein, and a liquid fat is essentially a solution in one proportion ur another of palmitin and stearin in olein. Olive, cottonseed, corn, linseed, and lard oils are types of this class of (Ails, all of which are soluble in ether, carbon disulphide, chloroform, hydrocarbons, etc.
All of the fatty oils are also capable of being saponified, i.e. of being broken up into glycerin and so-called fatty acids. The term 'saponifica tion' (from Lat. sago, soap) is used on account of the decomposition being °limiest elicited by the use of caustic soda or potash, which combines with the freed fatty acids to form the mixtures of salts well known as soaps. There arc, however, other methods by which the decomposition may be sometimes brought about. And since, what ever the method, the decomposition is accom panied by the chemical absorption of the ele ments of water, it is more exactly referred to, not as saponification, but as hydrolysis, or hydro lytic splitting. The several methods by which the hydrolysis of oils may lie brought about in clude: (1) Boiling with caustic alkali; (2) the action of steam under high pressure; (3) bacterial action, e.g. when fats become rancid; (4) the action of dry heat.
The following classification of these compounds by A. E. Allen will be found useful; it serves to illustrate the origin and approximate compo sition of the more common oils.
Mire Oil Gro-up, vegetable oleins, non-vola tile, high viscosity, non-drying, insoluble in al cohol.
Rape Oil Group, derived front the Cruciferfe, non-volatile. highest viscosity, non-drying, in soluble in alcohol.
Cottonsced Oil Group, non-volatile, medium viscosity, semi-drying, insoluble in alcohol.
Linseed Oil Group, drying oils, non-volatile, absorb oxygen, insoluble in alcohol, low viscosity.
Castor Oil Group, distinctly ditIcrent from the above in chemical composition by reason of con taining a large proportion of hydroxy-fatty acids including rieinoleic acid—highest viscosity, sol uble in alcohol and glacial acetic acid, non-vola tile, non-drying.
Lard Oil (Troup, animal oleins, non-volatile, non-drying, high viscosity.
117m/e Oil Group, marine animal oils, slightly volatile, low viscosity, partly drying, darken with chlorine, characteristic odor.
Palm and cocoanut oils are omitted because solid at ordinary temperatures. Sperm oil is not a true oil, but a liquid wax.
Plants contain a greater variety and, as a rule, relatively larger quantities of oils than animals. Vegetable oils are obtained by the simple process of grinding or crushing and hy draulic pressing of seeds or kernels, which con tain the largest proportion of oil. At times the ground materials are pressed cold and hot, the cold process yielding better produets, but smaller quantities. Of late years extraction processes using light hydrocarbon solvents are much used. The solvents are allowed to act on the crushed material at a slightly elevated temperature; on exhaustion, the liquid is drawn off, and the sol vent is separated by distillation. Oils produced by this process are very free from fonts or gelatinous material, lint, on the other hand. are liable to be contaminated with resins and color ing matters or any other material soluble in the solvent used. Animal oils occur in cells of putrescible tissue and require prompt rendering or extraction to retain their quality. Rendering may be of three types. viz.: ( 1 ) open-kettle rendering: (2) acid rendering; (3) steam ren dering. In the first process the fatty tissue is chopped. heated over water until the oil or fat is melted: and tried out. The broke? tissue shrivels and rises to the top, where it is skimmed obi and pressed to remove traces of oil. On cool ing.. the oil and water stratify, aad may be read ily separated. In acid rendering. the fatty tissue is, without previous treatment. ladled with water and sulphuric acid, which dissolves away the tissue and liberates the oil. In steam rendering the tissue is destroyed by treatment with steam under pressure in autoclaves, the exhaust of foul smelling gases being discharged into a chimney.