The oil is intimately mixed with one per cent of sulphuric acid. The mixture assumes a black color, the vegetable mucilage present in the oil becoming carbonized. After several days’ rest the oil becomes clear and floats on the surface of the sulphuric acid which has assumed a black color from the presence of finely divided carbon. The oil is decanted and treated, in the manner above stated for solid fats, with caustic soda lye. Heating can be dispensed with if the pumping is continued for a longer time.
Benzoin and benzoic acid have the property of counteracting the tendency of fats to become rancid; it is advisable, therefore, to mix intimately with the completely washed fat a small amount of benzoic acid, at most one-one-thousandth part by weight.
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.
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.
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.