Essential Oils.—The extraction and recovery of vegetable essential oils is performed by the following processes.
Enfieurage.—The simplest and most important of the processes adopted for recovering the perfumes of plants for industrial purposes is known as absorption or enfleurage. The earliest and most primitive method of performing this consists in allowing the flowers to lie between glass plates covered on both aides with grease, and superposed in piles in a frame, the flowers being renewed every day during the season, which may last for 8 days or 3 months. In absorbing by means of oil, instead of solid grease, the glass plates are replaced by frames of wire-gauze, covered with pieces of linen soaked in olive-oil, between which the flowers are spread and renewed as in the other case. The oil is squeezed out by the gentle action of a screw press. These primitive plans are still in wide use, despite their cost for labour, their slowness, and the risk of the absorbent grease becoming rancid.
A great improvement is the pneumatic method introduced by Piver, and illustrated in Fig.1040. The apparatus consists of a box a, about 10 ft. high and 6 ft. wide, containing wire-gauze trays b for holding the flowers ; between them, sheets of glass or silvered copper c, fixed at one side, but free on the three edges, receive the grease, not only in a flat layer, but divided into extremely fine drops, by being forced through a plate penetrated with minute holes. Two bellows d, arranged so that one falls while the other rises, maintain a current of air throughout the apparatus, by which the grease is rapidly impregnated• without the flowers coming into actual contact with it, thus avoiding the destruction of the perfume and staining of the grease, often arising from fermentation of the flowers in the presence of animal matters.
More recent improvements in the conduct of the absorption-process have been in the direction of replacing the grease by some neutral sub stance, such as paraffin, glycerine, and vaseline. In order to remove all traces of the paraffin from extracts obtained by its agency, it is recommended to subject them to a freezing-mixture, in order that all the stearoptene of the flowers may be deposited. Glycerine, concen
trated and inodorous, has been proposed by Himmel as superior to paraffin, on account of its fluid condition. Vaseline or cosmoline, ex tracted from petroleum residues, presents a great analogy to paraffin, except in having a consistence nearer that of glycerine. Vaseline has several advantages, and has been largely used ; it very readily absorbs the odours of those flowers which can he treated by heat. But there are many flowers which cannot be so treated, and it has been found that the alcoholic extracts made from impregnated vaseline rapidly lose their odour, even at the end of a month. On the whole, it is probable that the application of vaseline to enfleurage will be far less wide than was at first supposed.
Solvents.—The extraction of essential oils by means of solvents consists of three successive operations ;—(1) Solution of the oil by passing the solvent over the flowers placed in a percolator ; (2) distillation at a low temperature of the liquid obtained, to remove the wax mixed with the odoriferous body ; (3) evaporation of the last traces of the solvent in a water-bath. The solvent may be ether, chloroform, carbon biaulphide, petroleum-spirit, &c. Prof. Vincent, in combination with a perfumer named Massignou, has adopted chloride of methyl as a solvent for extracting essen tial oils, the chloride being previously treated in the gaseous state with concentrated sulphuric acid, to remove malodorous impurities. The oil-yielding body (flowers, &c.) is repeatedly digested for 2 minutes with charges of liquid chloride in a close vessel, the impregnated chloride passing into a receiver ; finally all traces are pumped from the digester into a vessel where the chloride is liquefied by oold compression ; a jet of steam is passed through the exhausted mass of flowers to drive out the chloride retained by the traces of water in the flowers. The liquefied saturated chloride is evaporated in vacuo, leaving the essential oil in the waxy and fatty residues. The essential oil is removed from the mass by treatment with cold alcohol. Apparatus capable of dealing with 1 ton of flowers daily has been erected on this principle at Cannes, S. France.