Horse-fat, and especially that from the fatty portions of the neck (Ger. Kammfett), as well as various other animal greases, are used in the manufacture of leather. They differ from tallow chiefly in that they have a lower melting-point, and contain more olein in proportion to the stearin and palmitin than true tallow, and are consequently somewhat softer. Though often almost white, these greases are sometimes darkened in colour by the products of putrefying animal matter, but this does not, as a rule, interfere with the oil being used for leather dressing. They are usually so cheap that they are but little adulterated; means of determining their purity are, however, given in L.I.L.B., p. 191.
Neatsfoot oil is a yellowish, nearly odourless oil, of bland taste, which is largely employed in the dressing of calf-kid. It has a similar composition to tallow oil and the other oils obtained by subjecting the soft animal fats to great pressure at a low temperature. It is often adulterated with bone oil, lard oil and cotton-seed oil, and occasionally with mineral oil and recovered wool-grease.
As neatsfoot oil is somewhat costly, curriers may with advantage often use ordinary animal greases (horse-fat, etc.) after they have had the harder tallow extracted by cooling and pressure, the product thus obtained being, chemically, the same as neatsfoot oil, and in every respect as suitable, while it is much less liable to adulteration.
The true neatsfoot oil is prepared by boiling the feet of cattle, and sometimes of sheep and horses, with water, and skimming off and clarifying the oil which is thus obtained.
The physical and chemical characteristics of this oil are described in L.I.L.B., p. 192.
Wool-Fat (Fr. Suint, oesype; Ger. Wollschweissfett) is a grease of high specific gravity, exsuded from the sebaceous glands of the sheep, together with organic salts of potassium. It is obtained by extracting wool with solvents; or by washing with alkaline solutions, from which it is recovered by precipitation with acid, and subsequent hot-pressing of the “magma,” or, more recently, by evaporating the scouring liquor to small bulk, and centrifugating. Wool-fat is characterised by its low percentage of glycerides, the fatty acids which it contains being mainly combined with higher alcohols (bodies of alcoholic structure, but of a waxlike consistency), and chemically it is rather a wax than a true fat. Among the alcohols which it contains is included a marked percentage of cholesterol and isocholesterol. It is difficultly saponifiable, requiring to be heated to 105-110° C. with alcoholic potash under pressure; and even then about 44 per cent. of alcohols remain, which are incapable of further saponification. Care must therefore be taken not to assume that unsaponifiable matter in greases which may contain wool-fat is necessarily mineral oil. For details of analysis see L.I.L.B., p. 194.
Pure wool-fat is nearly white, of salve-like consistency and very slight smell, with a density of 0·973 at 15° C. Crude wool-fat is yellow or brown, with an unpleasant and very persistent characteristic smell. Both the pure and the crude wool-fat have an extraordinary power of emulsifying with water, which makes them very valuable as substitutes for dégras in stuffing greases. Lanoline (and several other preparations under different names) are mixtures of purified wool-fat and water, of which lanoline contains about 22 per cent.
“Yorkshire grease” differs from crude wool-fat, in being recovered from the waters employed in scouring woollen cloths, as well as wool, and hence contains the free fatty acids of soaps used in scouring, as well as the “oleines,” etc., used in oiling the cloth, and although it often contains much wool-fat, it is occasionally destitute of this substance.
Holden Fat consists of ordinary wool-grease mixed with fish oil, and is used either as a substitute for, or in admixture with [dégras] (q. v.).
Distilled Wool Grease is produced by distilling crude Yorkshire grease with steam. Most of the glycerides are broken up, but many of the free fatty acids, alcohols and waxes distil over unchanged, though a considerable part is decomposed into volatile hydrocarbons strongly resembling mineral oils. The distillate is separated by cooling and pressure into a liquid “oleine” and a solid “stearine.” The latter forms a very valuable stuffing-grease which, in England, largely takes the place of the “oleo-stearine” used in the United States—with which, however, it must not be confounded.