Wool fat, or anhydrous lanolin, is a purified cholesterol fat obtained from the wool of the sheep, Ovis aries, Linn. (Order Ungulata). The natural grease is extracted from the wool by kneading with water, with which it readily forms an emulsion; on heating, it separates as a distinct layer at the surface of the liquid. Purification is effected by repeated treatment with water in a centrifugal machine, or by some other suitable process. Wool fat is also official in the U.S.P. It occurs as a light yellow, tenacious, fatty mass, having a slight, peculiar odour, and not readily becoming rancid. Melting-point, 40° to 44.4°. If 1 gramme of wool fat be boiled with 20 mils of alcohol and the solution filtered after cooling, the filtrate should not be rendered turbid by the addition of a 5 per cent. alcoholic solution of silver nitrate (absence of chlorides). A distinctive test for wool fat is that for cholesterol—1 gramme of the fat dissolved in 3 or 4 mils of acetic anhydride gives with 3 decimils (0.3 milliliter) of sulphuric acid a pink colouration, soon changing to green and blue. When a 2 per cent. solution in chloroform is gently poured over the surface of concentrated sulphuric acid it gradually develops a purple-red colouration at the junction of the liquids. If 10 grammes be heated with 50 mils of water on a water-bath the aqueous layer on filtration should not yield glycerin on evaporation, and when boiled with potassium hydroxide should not evolve the odour of ammonia (absence of nitrogenous organic matter). The saponification value of wool fat ranges from 90 to 102. It is practically impossible to saponify wool fat in aqueous solution of potassium hydroxide, but saponification may be effected by alcoholic potash under pressure; on evaporating the alcohol from the saponified liquid and dissolving the residue in water the cholesterol may be extracted by means of ether; on evaporating the ethereal liquid the cholesterol is left in the form of characteristic scaly crystals. Soft paraffin, being unsaponifiable, would be readily detected by the saponification test, and so also would glycerides by their much higher figures.
Insoluble in water; sparingly soluble in alcohol, more so in boiling alcohol (about 1 in 75), the hot alcoholic solution, on cooling, depositing most of the wool fat in the form of flocks; readily soluble in chloroform, ether, carbon bisulphide, acetone, benzene, or petroleum ether.
Constituents.—Wool fat contains the alcohols cholesterol and isocholesterol, together with various esters, the acids in combination being lanoceric, lanopalmitic, carnaubic, myristic, oleic, and probably cerotic and palmitic acids.
Uses.—Wool fat is closely allied to the natural secretions of the skin; recent experiments show that, in the pure state, it is not very readily absorbed, but when mixed with an equal quantity of olive oil or soft paraffin it readily penetrates the skin, and is useful for promoting the cutaneous absorption of drugs. Unlike lard it does not become rancid. It takes up about 50 per cent. of water, and is thus available for use in ointments in which the proportion of water is too great to permit of incorporation with any other fatty base. By the addition of a small quantity of wool fat to soft or liquid paraffin, the latter can be formed into stable emulsions with water, as in the preparation of parenols.
- Adeps Lanae Hydrosus, B.P. and U.S.P.—HYDROUS WOOL FAT.
- Wool fat, 70; distilled water, 30. Hydrous wool fat is employed as an ointment basis, generally for substances in aqueous solution. It may be mixed with olive oil, soft paraffin, or lard, by which its stickiness is much diminished and its absorbability increased.
- Unguentum Adipis Lanae, Ph.G.—WOOL FAT OINTMENT, Ph.G.
- Wool fat, 20; distilled water, 5; olive oil, by weight, 5.
- Unguentum Lanolini, B.P.C.—LANOLIN OINTMENT.
- Hydrous wool fat, 50; soft paraffin, 50. Mixes well with powders, oils, and aqueous solutions, and is a useful basis for dispensing purposes.
- Unguentum Lanolini Anhydrosi, B.P.C.—ANHYDROUS LANOLIN OINTMENT.
- Wool fat, 50; soft paraffin, 50.
- Unguentum Lanolini Oleosum, B.P.C.—OILY LANOLIN OINTMENT. Syn.—Wool Fat Ointment.
- Hydrous wool fat, 9; olive oil, 1. Used as an emollient, and as a basis for the application of drugs that are required to penetrate the skin.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.