Perfumes and their preparation

by George William Askinson

Acetic Acid (Acidum Aceticum).

Much confusion exists in the literature regarding the strength of acetic acid when merely called by this name. It is safe to assume that, in each country, the term applies to the acid officinal in its national pharmacopœia as “Acidum Aceticum.” Thus the Austrian and German pharmacopœias understand by it an acid containing 96% of absolute acetic acid, which is practically identical with what is known as glacial acetic acid. The latter is, in some pharmacopœias, distinguished by a special name: acidum aceticum glaciale, U.S. P.; acide acétique crystallisable, French Pharm.—In the present work, the author always intended the strong acid of the Austrian pharmacopœia to be understood when no other strength was designated. Like alcohol, strong acetic acid dissolves essential oils and is used in the manufacture of various toilet vinegars and washes. Acetic acid is made in chemical laboratories by distillation of acetate of sodium with sulphuric acid, or more commonly from wood vinegar. The buyer should always satisfy himself that the product is free from an empyreumatic odor which clings tenaciously to an insufficiently purified sample.

Fats.

Fats find extensive application in perfumery, in the preparation of the so-called huiles antiques, pomades, and many other cosmetics. They should be enumerated among the chemical products used in perfumery because they can never be employed in their commercial form, but must undergo some process of purification, which is effected less by mechanical than by chemical means. Commercial fats usually contain remnants of the animal or vegetable body from which they are derived: particles of blood and membranes occur frequently in animal fats; cell bodies and vegetable albumin in vegetable fats. Besides these mechanical impurities, fats, especially if old, sometimes contain small amounts of free fatty acids which suffice to impart to them the objectionable odor and taste peculiar to every rancid fat. While some fats, such as bear’s grease, butter of cacao, oil of sesame, and some others, remain free from rancidity for a long time, others undergo this change very rapidly; in fact, we may say that every fat which shows the slightest odor should be called rancid, for pure fat is absolutely odorless.

We shall here briefly describe the process employed in the fat industry and by perfumers for the purification of fats. Animal fat, such as lard, suet, bear’s grease, etc., as well as cocoanut and palm oils, are introduced into a large iron boiler containing dilute soda lye (not exceeding one per cent of caustic soda), and the lye is heated to boiling. In the boiler is a small pump terminating above in a curved tube having a rose of a watering-pot at the end. The pump is so arranged as to raise lye and melted fat at the same time and to return the fluid into the boiler in a fine spray. After the fat is melted, the solid matters floating on top are skimmed off with a perforated spoon, and then the pump is operated for about fifteen minutes. The contained shreds of membrane and similar substances are completely dissolved by the soda lye, the free fatty acids are perfectly combined, and the fat is at the same time decolorized. After cooling, it floats on the surface of the lye as a colorless and odorless fluid; it is ladled off and poured into tall tapering vessels which are well closed and preserved in cool cellars. Contact with the air, especially at higher temperatures, causes rancidity of the fat. For every twenty pounds of fat twenty quarts of lye are used.

According to another process the fat is purified by being heated with alum and table salt; or every twenty-five pounds of fat, one ounce of alum and two ounces of salt are dissolved in five gallons of water. The scum is carefully skimmed from the surface of the melted fat, and, after it has solidified, the fat is washed with water until the latter escapes perfectly tasteless and odorless.

The washing is a very complicated and tedious piece of work. Operating on a small scale, a slightly inclined marble slab is taken, upon which a thin stream of water is constantly falling from a tube arranged above it. The fat is placed on the slab in small quantities (not over two pounds) and ground with a muller, like oil colors, under a constant flow of water. Owing to the expense of hand labor, it is advisable to use a so-called vertical mill or chaser. This consists of a level, circular, horizontal marble slab, bearing a central, easily movable axis with a crosspiece upon which two, likewise vertical, cylindrical marble plates turn like wheels in a circle on the horizontal marble plate. The fat is placed on the latter and continually irrigated with water; behind every chaser is applied a marble plate with a blade which nearly touches the chasers and returns the fat displaced laterally, under the chasers. The axis around which the chasers run is kept moving by any available power, and the laborer has nothing to do but to replace the washed fat with crude.

Liquid fats are purified as follows:

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.