The 'general diffusion of fats and oils in the animal kingdom has been already described. (See FATS, AlintAL.) In the vezetable kingdom they are equally widely distributed. there being scarcely al-- tissue of plant in which traces of them may not be detected; but they are espec:ally abundant du the seeds. The seeds of the crucifi 7'03 are remarkably rich in oil; unseen yielding fully 20 per cent and rape-seed about 40 per cent of oil; and some fruits, as those of the olive and oil-palm, yield an abundance of oil.
The uses of the oils and fats era titunProu,s,,aud highly impottant; various members of this group being extensively emPkived as articles of food, itS medidines, as lubric4 big agents, in the preparation of soaps, plasters, ointments, varnishes, pigments, can dles and other means of illumination, for the purpose of dressing leather, etc. The fol lowing are the most important members of the group: 1. Vegetable Fate.—The chief solid fats of vegetable origin are cocoa-nut oil, nutmeg butter, and palm oil. The fluid vegetable fats or oils are divisible into the non-drying and the drying oils; the latter being distinguished from the former by their becoming dry and solid when exposed in thin layers to the air, in consequence of oxygenation; while the former do not absorb oxygen, but are converted by hyponitric acid or sub-oxide of mer cury into elaidine (as described m the article CILEINE), a reaction which is not exhibited by the drying oils. Some of the drying oils, especially linseed oil, when mixed with cotton, wool, or tow, absorb oxygen so rapidly, and consequently become so heated as to take fire, and many cases of the spontaneous combustion of heaps of oily materials that have been employed in cleaning machinery have been recorded. The drying prop erty may be much increased by treating the oils with a little litharge or oxide of man ganese, and linseed oil thus treated is then known as boiled oil. The chief non-drying oils are olive oil, almond oil, and colza oil; while the most important drying oils are those of linseed, hemp, poppy, and walnut; castor oil seems to form a link between these two classes of oils, since it gradually becomes hard by long exposure to the air.
2. Animal Fats.—The chief solid fats are suet, lard, butter, goose grease, etc.; while among the fluid fats or oils, sperm oil, ordinary whale oil, cod-liver oil, and neat's-foot oil may be especially mentioned. In many of their characters, spermaceti and bees-wax resemble the solid fats, but, as will be shown in the articles on these subjects, they are not glycerides. Asa general rule, stearine and palmitiue, both of which have comparatively high fnsin,sr points (between 1.57° and 114°), preponderate in the solid fats; while olcine, which is fluid at 32°, is the chief constituent of the oils.
One or two of the most important of the decompositions of the fats must be noticed. When any of these bodies are heated with the hydrated alkalies, they undergo a change which has long been known as saponification, or conversion into soap (q. v.), in which
the fatty acid combines with the alkali to form a soap, while the sweet viscid liquid glycerine is simultaneously formed. The combination of a fatty acid with oxide of lead forms a plaster. For further details on these points, the reader is referred to the articles Soar and PLASTERS.
The process of saponification affords a ready means of isolating the fatty acids, as the stearic or oleic acid may be at once separated from an alkaline stearate or olcate by the addition of hydrochloric or tartaric acid. When the fatty acids are, however, required on a large scale, as for the manufacture of the so-called stearine-candles, which in reality consist mainly of stearie and palmitic acids, sulphuric acid and the oil or fat are made to act upon each other at a high temperature. See CA.NDLE. The fatty acids may also be procured in a very pure form by the injection of superheated steam at a temperature of between 500' and 000° into heated fat—a process which, according to prof. Miller, " from its simplicity and from the purity of the products which it yields, Lids fair to supersede those previously employed in the preparation of the fatty acids for illuminating purposes." The only fatty acids which have been specially mentioned in this article are those which occur in natural glycerides, such as stearic, palmitic, and oleic acids. The term fatty acid has, however, in chemistry a wide signification, and is applied to many acids homologous to stearic acid, but not occurring in any natural this or oils. Thus stearic acid may be taken as the type of a group of acids (of which seventeen are already known) represented by the general formula, commencing with formic acid including acetic, propionic, butyric, valeric or Valerianie), eaproic, cenanthylie, caprylic, pelargonic, capric, Laurie, myristie, palmitic, stearic, arachidic, and cerotic acids, and terminating with melissic acid (C.116004). These are divided into the volatile and the true (or solid) fatty acids; the volatile acids being those from formic to capric acid, while the remainder, beginning with lauric acid, are the true fatty acids. The volatile fatty acids are fluid, and for the most part oily at ordino.y tempera tures, may be distilled without change, possess a pungent- odor, and are acid to the taste, and their solutions redden litmus paper strongly. The true fatty acids, on tire other hand. are solid at ordinary temperatures, are devoid of taste and smell, cannot be distilled, except in vacua, without decomposition, and only exert a slight action cn litmus. The volatile acids occur in the animal and vegetable kin,t1donis (formic acid, for example, in red ants, and valeric acid in the root of valerian), and they are likewise produced by the oxidation and spontaneous decomposition of numerous animal and vegetable products. The entire series, up to capric acid, may be obtained by oxidizing oleic acid with nitric acid. The true or solid acids only occur as constituents of ani mal and vegetable fats.