PROPERTIES OF THE OILS AND FATS.

297

linseed oil, in undergoing this change do not evolve any gas; but during the solidification of most others, an evolution of carbonic anhydride, attended sometimes with an escape of hydrogen, takes place.

The non-drying oils do not absorb oxygen, but are converted into elaidin, by means of mercurous nitrate or by peroxide of nitrogen, a reaction of which those of the first variety are not susceptible. The solidification of olive oil is effected by a quantity of peroxide of nitrogen, not exceeding of the weight of the oil (1298).

The principal drying oils are those known as linseed, walnut, hemp, poppy, and cod-liver oil. The absorption of oxygen by some of these oils, and consequent elevation of temperature, is, under favourable circumstances, so rapid as to be attended with heat sufficient to cause the mass to take fire; and several serious conflagrations have been traced to the spontaneous ignition of cotton, wool, or tow, soaked in oil, which had been thrown aside in refuse heaps after it had been used in cleaning machinery. The siccative or drying property of these oils may be much increased by heating them with about one-twentieth of their weight of litharge, which becomes completely dissolved by the oil. Oxide of manganese may be used for the production of a similar effect: linseed oil which has been thus treated is technically known as boiled oil. Chevreul, however, states that it is unnecessary to heat the oil for so long a time, or to so high a temperature as is commonly practised; linseed oil heated to 140° (60° C.) in contact with one-tenth of its weight of oxide of manganese, having acquired powerful siccative properties.

The drying oils are not solidified by contact with peroxide of nitrogen, or with mercurous nitrate, and a fraudulent mixture of them with olive or almond oil may thus be detected. The oleic acid which they furnish on saponification, differs from ordinary oleic acid, and absorbs oxygen much more rapidly than the latter; and in consequence of this oxidation it speedily becomes converted into a transparent solid varnish. For a careful investigation of the changes which occur during the drying of oils, the reader is referred to a paper by Chevreul (Ann. de Chimie, III. xlvii. 209). The most important of the oils which do not become dry by exposure to the air are olive oil, almond oil, rape oil, and colza oil, besides many animal oils.

Tomlinson (Phil. Mag. 1861, p. 249) has indicated a method of distinguishing different oils from each other, and in many cases of detecting the admixture of a cheaper with a more valuable oil,

298

COMPOSITION AND PROPERTIES OF VARIOUS OILS.

It consists in allowing a drop of each oil to spread over the surface of water, in a vessel 4 or 6 inches in diameter (12 or 15 centimetres). The dish must be scrupulously freed from every trace of grease. On observing the phenomena of colour exhibited by the film of oil as it spreads upon the water, and watching the way in which it gradually breaks up, characteristic differences may be noticed, which, with a little practice, enable the experimenter readily to distinguish the more important varieties of oil from each other.

(a) Composition and Properties of the principal Oils and Fats.

(1221) 1. Olive oil (Sp. gr. 0918) is prepared in great abundance in the southern countries of Europe; it furnishes the principal oily material employed in making Marseilles and Castile soap. The ripe olives are first subjected to pressure without the application of heat, and in this manner the finest oil, or virgin oil, is obtained: the residue is afterwards heated with water, and a large quantity of an inferior mucilaginous oil rises to the surface; it is this which is chiefly employed in soap-making. The oil is always of much finer quality if extracted immediately after the fruit has been crushed, as otherwise it experiences a kind of fermentation, which injures the flavour of the product. The solid ingredient in olive oil is almost exclusively margarin. Olive oil soon becomes rancid when kept; it becomes partially few degrees below 32°.

solid at a

2. Almond oil (Sp. gr. 0·918 at 60°) solidifies at about -13°. It is much less extensively employed than olive oil; it is extracted from the kernel of the Amygdalus communis, by a process similar to that adopted for olive oil.

3. Colza oil [Sp. gr. 0·913 at 22° (5°5 C.)] becomes nearly solid. It is largely used for illuminating purposes, and is obtained from the seeds of the Brassica oleifera. It is of a yellow colour, and is nearly free from odour. Colza oil is sparingly soluble in cold alcohol, but is readily dissolved by boiling alcohol.

(1222) 4. Linseed oil (Sp. gr. 0939 at 54°) remains liquid till within a few degrees of o° F. This oil is pressed from the seeds of the Linum usitatissimum, which yield about one-fifth of their weight of it. It has a slight peculiar odour, and is of a yellow colour. Owing to its powerful drying properties, which are much increased after heating it with a small quantity of litharge or of peroxide of manganese, it is extensively used as a vehicle

COMPOSITION AND PROPERTIES OF VARIOUS OILS.

299

for mixing with colours for painting in oil: it is also largely employed in the preparation of printer's ink, in the preparation of black enamel for leather, and in the varnishing of oiled silk. If exposed for some time to a high temperature it becomes converted into a dark tenacious mass, which when cold may be drawn out into threads; in this state, if mixed with lampblack, it constitutes printer's ink. If the tenacious residue obtained by heating the oil be boiled for some hours with dilute nitric acid, it acquires a consistence resembling that of ordinary lead plaster, and becomes hard on exposure to the air; but it softens again by the heat of boiling water, and acquires a consistence resembling that of caoutchouc, for which it has been substituted in some instances. This caoutchouc of oils is soluble in oil of turpentine, in carbonic disulphide, and in dilute alkaline solutions; on neutralizing these alkaline solutions of the caoutchouc by means of an acid, the caoutchouc is precipitated unaltered. Other drying oils beside linseed oil yield a similar substance, though less abundantly.

The oleic acid furnished by the saponification of linseed oil differs from ordinary oleic acid; Sacc terms it linoleic acid, and assigns to it the formula (HO,CHO?) more probably (H,H). It absorbs oxygen rapidly from the air, even when combined with oxide of lead and other bases.

(1223) 5. Sperm oil (Sp. gr. 0868) is the liquid portion of the fat of the spermaceti whale: it becomes semisolid at about 45° (7°C.) It is of a yellow colour, and has a disagreeable odour and taste, due to the presence of a small quantity of a peculiar oil, termed phocenin by Chevreul; this body when saponified yields glycerin, and a volatile acid, apparently identical with the valeric. The other constituents of the oil are palmitin and olein. The olein contained in sperm oil differs from that of olive oil, since, although it becomes solid under the action of peroxide of nitrogen, it possesses a drying quality. Sperm oil may be purified by agitating 100 parts of the oil with a mixture of 4 parts of chloride of lime and 12 of water; a small quantity of decoction of oak bark is afterwards added to remove traces of a gelatinous matter which it retains, and the mixture is left to settle; the clear oil is afterwards agitated with a small proportion of sulphuric acid, again clarified by subsidence, and washed to remove adhering sulphuric acid.

6. Ordinary whale oil (Sp. gr. o'927) does not become solid above 32°. It is of a darker yellow colour, and has a more disagreeable odour than the foregoing oil.

300

COD-LIVER OIL-CASTOR OIL.

7. Cod-liver oil (Sp. gr. o'928) has acquired importance from its extensive employment as a therapeutic agent. It is extracted from the liver of the Gadus morrhua, or common cod fish. Its colour varies from a pale, scarcely perceptible yellow, to a deep brown, according to the mode of its extraction. It has a peculiar fishy odour and taste. In addition to the usual components of the fish oils, it appears to contain a compound of acetic acid with glycerin (acetin, 1240); it also contains a certain proportion of the constituents of the bile, and a small quantity of a phosphorized fat, besides minute quantities of iodine and bromine in a state of combination with some organic substance. Ether dissolves the oil without difficulty, but cold alcohol takes up only a small quantity of it. The iodine and bromine are not in the form of a metallic iodide or bromide; indeed, their presence cannot be detected until the oil has been saponified and the soap charred. When a drop of concentrated sulphuric acid is allowed to fall into the oil it produces a beautiful crimson colour, owing to the action of the acid upon the biliary matter present.

8. Castor oil (Sp. gr. 0·969) is of a very viscid consistence, but it does not become solid even at a temperature of o° F. This oil is obtained from the seeds of the Ricinus communis; it forms a connecting link between the drying and non-drying oils, since it gradually becomes hard by long exposure to air. Castor vil has an acrid taste, which it is stated may be removed by agitation with magnesia. Castor oil differs from the other fixed oils in being soluble in alcohol in all proportions. The principal acid obtained by its saponification is a modification of oleic acid, termed ricinoleic acid (H,H), which remains fluid at a temperature considerably below 32°. By the action of peroxide of nitrogen it becomes converted into a solid isomeric fat, termed ricinelaidic or palmic acid. When treated with ammonia, castor oil yields a solid crystalline amide, ricinolamide (Є18H3N2). NᎾ The oil, when distilled, furnishes œnanthylic acid (H¤,H1Ð1⁄2 7 13 1288), and a large quantity of the aldehyd of this acid (E,H10; 1255), which was termed œnanthol by Bussy. When castor oil is distilled with caustic potash it is decomposed, the principal products being sebacic acid (1306), which remains in the retort in the form of potassic sebate, whilst hydrogen gas is liberated, and a quantity of a volatile liquid (octylic or caprylic alcohol mixed with caprylic aldehyd), is distilled over (1256).

14

2

(1224) The Solid Fats.-The solid fats of vegetable origin which are in most frequent use are cocoa-nut oil, nutmeg-butter,

COCOA-NUT OIL-PALM OIL-BUTTER.

301

and palm oil; those of animal origin are butter, suet, lard, spermaceti, and bees' wax.

Palm oil, nutmeg butter, and cocoa-nut oil, each contain a different solid fatty acid, which, in combination with the hydrocarbon glycerin (Є,H), constitutes the principal portion of the solid part of the oil.

1. Cocoa-nut oil [Fusing pt. about 68° (20° C.)] is obtained from the Cocos nucifera. It is largely consumed in the manufacture of candles; it is also used in the preparation of some of the lower priced kinds of soap (1233). Cocoa-nut oil is a very complex fat, for it yields not fewer than six different acids on saponification. These acids, according to Georgey, are

Cocoa-nut oil probably also contains oleic acid, since it yields sebacic acid when distilled.

2. Palm oil, which is of a bright orange or golden yellow colour, is produced from the pulp of the ripe fruit of the Elais guineensis. The oil is obtained by heating the crushed fruit with boiling water. It has an agreeable odour resembling that of violets. The solid portion of palm oil consists chiefly of a peculiar fat, which has received the name of palmitin, and which, when saponified, yields palmitic acid (HЄ16H31→2). Palm oil speedily becomes rancid when kept, and though when fresh it melts at about 81° (27° C.), it gradually becomes less fusible, till it remains solid at a temperature of 100°. This change is due to the spontaneous decomposition of the palmitin, and the liberation of palmitic acid, under the influence of an azotised constituent of the fruit, which accompanies the oil in the process of extraction. Palm oil is readily decolorized by exposure to air at a high temperature, but it is more usual to effect this bleaching of the oil by the addition of a small quantity of sulphuric acid and potassic dichromate. This oil constitutes an important article of commerce, upwards of 20,000 tons being annually imported from the western coast of Africa. It is consumed in immense quantities in the manufacture of candles and of soap.

3. Butter consists of a mixture of olein with several fats, amongst which palmitin is the principal solid constituent. According to Heintz, the solid portion of butter contains, in addition to palmitic acid, another acid, termed by him butic acid,