The best way of preserving fats is by salicylic acid. This is added to solid fats while they are in a melted state; if oils, the acid is poured in and the bottle vigorously shaken. If the oil is in casks, a small bag filled with salicylic acid is hung into it from the bung-hole. The acid dissolves in the oil and is disseminated through it and thus effects its preservation. One-one-thousandth part by weight of the fat or oil is said to be more than sufficient to keep it perfectly fresh for years.
Fats differ largely in their physical properties—for instance, in their appearance, melting-point, firmness, etc. As we shall return to this subject in connection with the manufacture of some perfumes, it is enough here to state briefly that by the addition of spermaceti, wax, paraffin, etc., fats are made more transparent and firmer—a matter of importance for some cosmetic preparations.
Chinese Gelatin.
This substance, derived from several algæ, species of Eucheuma, indigenous to the Chinese sea, and identical with Japanese agar-agar, on being boiled with two hundred parts of water has the property of forming a colorless solution which solidifies on cooling. Owing to this property the addition of a small quantity of Chinese gelatin (0·1-0·2%) is an excellent means for imparting to certain pomades and ointments great transparency and firmness.
Fruit Ethers
are liquids which possess an agreeable, refreshing odor resembling that of some fruits. For this reason they are used in confectionery, in the manufacture of liqueurs, and also in many ways in perfumery. Chemically, fruit ethers are combinations of an organic acid—acetic, butyric, valerianic, etc.—with a so-called alcohol radicle such as ethyl and amyl. Their manufacture is connected with many difficulties and is but rarely attempted by perfumers, especially as these products are made a specialty in some chemical laboratories and are furnished at very low prices and of excellent quality. In perfumery the following fruit ethers are particularly employed.
Acetic Ether,
prepared by the distillation of acetate of sodium with alcohol and sulphuric acid, is a colorless liquid having an odor of fermenting apple juice, with a boiling-point at 74° C. (155° F.).
Pine-apple Ether
(ether or huile d’ananas) is made by the saponification of butter with solution of potassa, distillation of the soap with alcohol and sulphuric acid, and rectification of the distillate. It is an inflammable liquid with an intense odor of pine-apple; its boiling-point is 119° C. (246° F.). It is not generally used pure, as its odor needs some correction. This is accomplished by the addition of a little valerianate of amyl, and chloroform. Also in other ways.