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 butterfat, 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 hst below the most important fatty acids occurring in oils and fats are enumerated (cf. Waxes, below).

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 embrj'O, whereas in animals the oils and fats are enclosed mainly in the cellular tissues of the intestines and of the back.

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Boiling-point.

Melting-point. "C.

Characteristic of

mm.

°C.

Pressure.

I. Acids of the Acetic series CnHjnOz

Acetic acid

C2H.O2

760

119

17

Spindle-tree oil, Macassar oil

Butyric acid .......

C.H8O2

760

162-3

-6-5

Butter fat, Macassar oil

Isovaleric acid

CsHioOa

760

173-7

-51

Porpoise and dolphin oils

Caproic acid

C6H12O2

770

202-203

-8

/ Butter fat, coco-nut oil,

Caprylic acid

C8H16O2

761

236-237

16-5

I palm nut oil

Capric acid

C10H20O2

760

268-270

31-3

Lauric acid

C12H24O2

100

225

43-6

Laurel oil, coco-nut oil

Myristic acid

CuHoaO^

100

250-5

53-8

Mace butter, nutmeg butter

Isocetic acid (?)

C16H30O2

55

Purging nut

Palmitic acid

C16H32O2

100

271-5

62-62

Palm oil, Japan wax, myrtle wax, lard, tallow, &c.

Stearic acid

CigHaeOj

100

291

69-32

Tallow, cacao butter, &c.

Arachidic acid

C20H 4002

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 CnHa^sOj

Tiglic acid

C5H8O2

760

198-5

64-5

Croton oil

Hypogaeic acid

CeHsoOj

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 C„H2n-i02

Linolic acid

C18H32O2

Maize oil, cotton-seed oil

Tariric acid

C18H32O2

50-5

Oil of Picramnia Camboita

Telfairic acid

C,8H3202

13

220-225

Koeme oil

Elaeomargaric acid

C18H32O2

48

Tung oil

IV. Acids of the cyclic Chaulmoogric series

C„H2, ^402

Hydnocarpic acid

Cl6H2802

59-60

/ Hydnocarpus, Lukrabo and ) Chaulmoogra oils

Chaulmoogric acid

C18H32O2

20

247-248

68

V. Acids of the Linolenic series Ct.H2, ^602

Linolenic acid

C18H 3002

f Linseed oil

Isolinolenic acid

C18H30O2

VI. Acids of the series CnH2n-802

Clupanodonic acid

C18H28O2

(liquid)

Fish, liver and blubber oils

VII. Acids of the Ricinolelc series CnH2„ 203

Ricinoleic acid

C18H34O3

15

250

4-5

Castor oil

Quince oil acid

C18H34O3

Quince oil

VIII. Dihydroxylated acids of the series C„H2„04

Dihydroxystearic acid

C18H36O4

141-143

Castor oil

IX. Acids of the series C^H.^-^O, -

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(0-Ci8H360)2, (O-CisHssO), and stearo-palmito-olein, C3H5(0-Ci8H350) (0-C,6H3iO) (0-C,8H330). Such glycerides are termed " mixed glycerides." The glycerides occurring in natural oUs 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.

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 m.after " are phytosterol C26H440 or C27H440(?), and the isomeric

cholesterol. The former occurs in all oils and fats of vegetable