Page:EB1911 - Volume 20.djvu/66

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	${\Bigg \}}$	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	${\Big \}}$	Hydnocarpus, Lukrapo and Chaulmoogra oils
	Chaulmoogric acid	C18H32O2	20	247–248	68
V.	Acids of the Linolenic series C𝑛H2𝑛−6O2—
	Linolenic acid	C18H30O2	..	..	..	${\Big \}}$	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