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OILS


constituents of most oils and fats, but latterly there have been recognized as widely distributed trilinolin, the glyceride of linolic acid, and trilinolenin, the glyceride of linolenic acid. The two last-named glycerides are characteristic of the semi-drying and drying oils respectively. In addition to the fatty acids mentioned already there occur also, although in much smaller quantities, other fatty acids combined with glycerin, as natural glycerides, such as the glyceride of butyric acid in butter-fat, of caproic, caprylic and capric acids in butter-fat and in coco-nut oil, lauric acid in coco-nut and palm-nut oils, and myristic acid in mace butter. These glycerides are, therefore, characteristic of the oils and fats named.

In the classified list below the most important fatty acids occurring in oils and fats are enumerated (cf. Waxes, below).

Boiling-point.  Melting-point.
°C.
Characteristic of
mm. 
Pressure
°C.
I. Acids of the Acetic series C𝑛H2𝑛O2
 Acetic acid C2H4O2 760 119 17 Spindle-tree oil, Macassar oil
 Butyric acid C4H8O2 760 162·3 −6·5 Butter fat, Macassar oil
 Isovaleric acid C5H10O2 760 173·7 −51 Porpoise and dolphin oils
 Caproic acid C6H12O2 770 202–203 −8 Butter fat, coco-nut oil, palm nut oil
 Caprylic acid C8H16O2 761 236–237 16·5
 Capric acid C10H20O2 760 268–270 31·3
 Lauric acid C12H24O2 100 225 43·6 Laurel oil, coco-nut oil
 Myristic acid C14H28O2 100 250·5 53·8 Mace butter, nutmeg butter
 Isocetic acid (?) C15H30O2 .. .. 55 Purging nut
 Palmitic acid C16H32O2 100 271·5 62·62 Palm oil, Japan wax, myrtle wax, lard, tallow, &c.
 Stearic acid C18H36O2 100 291 69·32 Tallow, cacao butter, &c.
 Arachidic acid C20H40O2 .. .. 77·0 Arachis oil
 Behenic acid C22H44O2 .. .. 83–84 Ben oil
 Lignoceric acid C24H48O2 .. .. 80·5 Arachis oil
II. Acids of the Acrylic or Oleic series C𝑛H2𝑛−2O2
 Tigic acid C5H8O2 760 198·5 64·5 Croton oil
 Hypogaeic acid C16H30O2  15 236 33–34 Arachis oil
 Physetoleic acid C16H30O2 .. .. 30 Caspian seal oil
 Oleic acid C18H34O2 100 285·5–286 14 Most oils and fats
 Rapic acid C18H34O2 .. .. .. Rape oils
 Erucic acid C22H42O2  30 281 33–34 Rape oils, fish oils
III. Acids of the Linolic series C𝑛H2𝑛−4O2
 Linolic acid C18H32O2 .. .. .. Maize oil, cotton-seed oil
 Tariric acid C18H32O2 .. .. 50·5 Oil of Picramnia Camboita
 Telfairic acid C18H32O2 13 220–225 .. Koëme oil
 Elaeomargaric acid C18H32O2 .. .. 48 Tung oil
IV. Acids of the cyclic Chaulmoogric series C𝑛H2𝑛−4O2— 
 Hydnocarpic acid C16H28O2 .. .. 59–60 Hydnocarpus, Lukrapo and Chaulmoogra oils
 Chaulmoogric acid C18H32O2  20 247–248 68
V. Acids of the Linolenic series C𝑛H2𝑛−6O2
 Linolenic acid C18H30O2 .. .. .. Linseed oil
 Isolinolenic acid C18H30O2 .. .. ..
VI. Acids of the series C𝑛H2𝑛−8O2
 Clupanodonic acid C18H28O2 .. .. (liquid) Fish, liver and blubber oils
VII. Acids of the Ricinoleic series C𝑛H2𝑛–2O3
 Ricinoleic acid C18H34O3  15 250 4–5 Castor oil
 Quince oil acid C18H32O3 .. .. .. Quince oil
 VIII. Dihydroxylated acids of the series C𝑛H2𝑛O4
 Dihydroxystearic acid C18H36O4 .. .. 141–143 Castor oil
IX. Acids of the series C𝑛H2𝑛–2O4
 Japanic acid C22H42O4 .. .. 117·7–117·9 Japan wax

Up to recently the oils and fats were looked upon as consisting in the main of a mixture of triglycerides, in which the three combined fatty acids are identical, as is the case in the above-named glycerides. Such glycerides are termed “simple glycerides.” Recently, however, glycerides have been found in which the glycerin is combined with two and even three different acid radicals; examples of such glycerides are distearo-olein, C3H5(O·C18H35O)2, (O·C18H33O), and stearo-palmito-olein, C3H5(O·C18H35O) (O·C16H31O) (O·C18H33O). Such glycerides are termed “mixed glycerides.” The glycerides occurring in natural oils and fats differ, therefore, in the first instance by the different fatty acids contained in them, and secondly, even if they do contain the same fatty acids, by different proportions of the several simple and mixed glycerides.

Oils and fats must, therefore, not be looked upon as definite chemical individuals, but as representatives of natural species which vary, although within certain narrow limits, according to the climate and soil in which the plants which produce them are grown, or, in the case of animal fats, according to the climate, the race, the age of the animal, and especially the food, and also the idiosyncrasy of the individual animal. The oils and fats are distributed throughout the animal and vegetable kingdom from the lowest organism up to the most highly organized forms of animal and vegetable life, and are found in almost all tissues and organs. The vegetable oils and fats occur chiefly in the seeds, where they are stored to nourish the embryo, whereas in animals the oils and fats are enclosed mainly in the cellular tissues of the intestines and of the back.

Since the methods of preparing the vegetable and animal fats are comparatively crude ones, they usually contain certain impurities of one kind or another, such as colouring and mucilaginous matter, remnants of vegetable and animal tissues, &c. For the most part these foreign substances can be removed by processes of refining, but even after this purification they still retain small quantities of foreign substances, such as traces of colouring matters, albuminoid and (or) resinous substances, and other foreign substances, which remain dissolved in the oils and fats, and can only be isolated after saponification of the fat. These foreign substances are comprised in the term “unsaponifiable matter.” The most important constituents of the “unsaponifiable matter” are phytosterol C26H44O or C27H44O(?), and the isomeric cholesterol. The former occurs in all oils and fats of vegetable