crystals which are deposited from olive oil on exposure to cold are a chemical compound of margarine and oleine (Liebig).

Margaric acid (the oily acid peculiar to margarine) is most easily obtained by heating impure stearic acid (such as the stearine used for making candles) with its own weight of common nitric acid for a few minutes. The fatty acid which is deposited as the solution cools contains a little oleic acid; to remove which, the mass is compressed between folds of blotting paper, and dissolved and crystallized from alcohol several times successively, till its melting point remains constant at 140° (Liebig). In appearance, margaric acid greatly resembles stearic, but it is more fusible. Its alcoholic solution has an acid reaction. The formula of the anhydrous acid is C6s H66 06.

Margaric acid, like stearic, forms with potash and soda neutral and acid salts, the latter containing half as much alkali as the former. The neutral salts are readily soluble in water, and the solutions afford precipitates of the acid salts or bimargarates when very largely diluted. The neutral margarate of potash is rather soft, but the neutral margarate of soda is somewhat harder. The formula of the neutral stearate of soda is 2NaO+C68 H66 О6.

Oleine, or oleate of glycerine, forms the principal constituent of oils, and may be obtained, though not in a state of purity, by subjecting congealed almond oil to pressure. The fluid portion which exudes is oleine, generally containing in solution either stearine or margarine, or both. At a very low temperature, oleine solidifies. If quite free from foreign matters capable of exciting a fermentative decomposition,

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oleine does not become rancid, but this body is more liable to decomposition than either stearine or margarine. The oleine of drying oils appears to be a distinct substance from the oleine of fat oils (Redtenbacher).

Oleic acid is an oily liquid of a faint yellowish tint, having an acid reaction on test-paper, a very weak odour, and a pungent taste. When cooled to some degrees below the freezing point of water, it becomes a mass of crystalline needles. It is soluble in alcohol and ether, and is more easily decomposed than any other of the oily acids. The soapy compounds which oleic acid forms with potash and soda are both soft and very soluble in water, unless they contain an excess of acid. The composition of oleic acid has not been decided with certainty. According to the analysis of M. Varrentrapp, the formula of the hydrated acid is HO + C1 H3, O4.

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Glycerine.-In a state of purity, glycerine is a syrupy liquid, inflammable, inodorous, but very sweet to the taste, and was hence named by Scheele, its discoverer, the sweet principle of oils. It is miscible with water and alcohol in all proportions. It cannot be distilled alone without decomposition, but partially volatilizes when boiled with water. It is not fermentable, nor is it subject to spontaneous decomposition. In its solvent power on alkaline and metallic salts and other bodies, glycerine is nearly equal to water. It unites with sulphuric acid to form an unstable compound, which possesses the properties of an acid.

The most convenient method of preparing glycerine is to saponify olive oil with oxide of lead (litharge) and a little water, by boiling them together;

the soap of oxide of lead then formed is insoluble in water, but the liberated glycerine dissolves, accompanied by a small quantity of oxide of lead, which may be removed by passing a current of sulphuretted hydrogen gas through the liquid. After being filtered and carefully evaporated, the liquid leaves a residue of glycerine nearly pure.

It is obvious from what has already been stated, that the consistence of oils and fats must be related to the proportion in the oil or fat of oleine on the one hand, and of stearine and margarine on the other. If oleine predominates, it is liquid, and the temperature at which it solidifies is lower in proportion as the oleine is in excess; if margarine is the principal constituent, the consistence is about that of lard; but if stearine is most abundant, the fat is firm, like mutton suet. The principal oily and fatty matters hitherto minutely investigated, which contain in combination with glycerine other fat acids than those which have just been described, are, palm oil, train oil, butter of the cow, butter of nutmegs, butter of the cocoa-nut, the fat of the goat, and castor-oil.

Besides stearine, oleine, and margarine, most oils and fats contain in their ordinary state small quantities of foreign colouring and odoriferous matters, which vary with the different kinds, and which may be removed without affecting the essential characters of the oil or fat.* They also contain more or less albuminous or similar azotized matters common to all

* In most cases, such matters may be almost entirely removed by digesting the oil or liquefied fat with animal charcoal for twenty-four hours. The foreign bodies present in oils used for burning in lamps considerably decrease the brilliancy of the flame and also tend to clog

plants, as membrane and mucus, which act like yeast in exciting a fermentative decomposition of many organic bodies with which they are in contact. To the presence of these matters, the rancidity which most oils acquire on exposure to the air, partly through the absorption of oxygen, may be ascribed; for pure stearine, margarine, and oleine do not become rancid on exposure to the air. A rancid oil contains the oily acids in a free state, and a volatile body to which the peculiar odour is due.

The

Many oils, when exposed to the air, become converted through the absorption of oxygen into a tough, transparent, resinous mass or varnish, which does not afford an oily stain to paper; but others do not dry on exposure to the air, though they may become somewhat more consistent. Hence a well-marked distinction of oils into two classes, drying oils and fat oils. The former form soft soaps with alkalies, and the latter, if of vegetable origin, hard; and the former do not solidify like the latter when mixed with nitrous acid, or nitrate of suboxide of mercury. oleic acid of drying oils appears to be a distinct subthe wick. Oil intended for burning may be conveniently purified by strongly agitating it with two or three parts per cent. of concentrated sulphuric acid, which would have no action on the oil, but cause the separation of the foreign matters in brown flocks. The mixture should be allowed to remain at rest for twenty-four hours, and be then heated by introducing steam, till its temperature rises to 160° or 170° Fahr. It is then allowed to stand quiet for three or four days, during which time it settles into three strata: the uppermost stratum is the purified oil, which should be washed with water, and filtered through cotton placed between perforated metallic plates; the middle stratum is brown impure oil, from which, after a time, an additional quantity of pure oil may be obtained; and the lowermost is water charged with sulphuric acid and the products of the decomposition of the foreign matters. Such a process as this was long ago devised by M. Thénard.

stance from the oleic acid of fat oils. It dries in the air to a resinous mass, like the oil from which it is derived.

Tallow is the concrete fat of oxen, deer, and large quadrupeds in general, melted and separated from the fibrous matter with which it is at first accompanied. It consists chiefly of stearine, with a little oleine, and is firm, brittle, and has a peculiar and heavy odour. It soon becomes rancid on exposure to the air. As met with in commerce, it usually has a yellow tinge; but when pure it is white, and nearly insipid. It is divided into two chief varieties, according to its purity and consistence, namely, candle and soap tallow; and these are subdivided into other classes, according to the colour of the tallow, and (if foreign) to the place from whence it is imported. Its quality depends in some degree on the animal from which it is procured; but more, probably, on the care observed in its preparation. It is generally sufficiently pure to be used in soap-making without any previous purification.

Besides a great quantity of tallow supplied by the home slaughter, about sixty thousand tons per annum are regularly imported into the United Kingdom, by far the greater part of which is brought from Russia. Of late years, considerable importations of tallow have been made from the States of the Rio de la Plata. The price of "soap tallow" from St. Petersburgh and Siberia is generally about two pounds or guineas per hundred-weight, and that of British a little higher.

In the manufacture of the coarser kinds of white