This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Source, etc. - Wool fat is a fatty or, more correctly, waxy substance secreted by the hairs constituting the fleece of the sheep Ovis aries, Linne (Phylum Ghordata, Sub-phylum Craniata, Class Mammalia, Order Ungulata).
If a few threads of raw sheep's wool are examined under the microscope little masses of a fatty substance may be seen adhering to them. This is the crude, natural, wool fat; part of it is soluble in water and is removed during the first cleansing process which consists in steeping the fleeces in water; part is insoluble in water and can subsequently be removed by benzene, acetone, or other suitable solvent, forming, after evaporation, a brownish grease. It is also removed when the fleeces are scoured with soap and water, the second cleansing process. When the emulsion thus produced is acidified the wool fat is separated together with the fat-acids produced by the decomposition of the soap. These fat-acids can be converted into the corresponding calcium salts and the wool fat separated by treating the product with acetone; the acetone solution, evaporated to dryness, yields crude wool fat which has to be purified by suitable means.
Wool fat may also be extracted by scouring the fleeces with hot water, and allowing the emulsion thus produced to stand, when impure wool fat rises as a cream. This can be cleansed by repeatedly mixing with water and separating by centrifugation, the resulting wool fat being subjected to a final process of purification.
Purified wool fat is a yellowish, tenacious, unctuous solid with a characteristic odour. It melts at about 42° and is soluble in acetone, benzene, and the usual fat solvents. It may be distinguished from other fats by its solubility in boiling alcohol and also by the following test (for cholesteryl alcohol): Dissolve 0.1 gramme in a mixture of 5 c.c. of chloroform and 0.5 c.c. of acetic anhydride; pour gently upon 5 c.c. of sulphuric acid; a purplish brown ring, passing into green is developed at the surface of contact.
Wool fat consists chiefly of cholesteryl and iso-cholesteryl alcohols combined with lanoceric, lanopalmitic, carnaubic, myristic, a little oleic, and possibly also palmitic and cerotic acids.
Wool fat is largely used as an emollient and for promoting the absorption of drugs by the skin.
The most probable adulterants of wool fat are mineral fats (soft paraffin) or animal and vegetable fats and oils. Wool fat, like most waxes, is not readily attacked by boiling, aqueous solution of potassium hydroxide, but may be saponified by boiling, or heating under pressure, with an alcoholic solution of the same, the saponification value varying from 90 to 102. Mineral fats are not attacked by either aqueous or alcoholic solution of potassium hydroxide, and their presence would lower the saponification value. Animal and vegetable fats and oils would by the same treatment be saponified and raise the saponification value; they would also be saponified by aqueous alkalies which would not attack wool fat or mineral fats. Glycerin can be detected by shaking the wool fat with hot water and evaporating the aqueous solution.