In America, Prof. Seeley's method of applying gasoline as a solvent of essential oils has been largely used for extracting the valuable principle of hops.
Expression and Scarification.—Such processes as are described in this section are adapted only to materials yielding a large proportion of essential oil, such as the fruits of the Citrus genus. The simplest form is the so-called " sponge-process." The peel is first cut off the fruit in 3 thick longi tudinal slices, leaving the central pulp of triangular shape, with a little' peel at either end ; the central pulp is cut transversely in the middle, and thrown on one side, while the peel is collected on the other. The latter is left till next day, then treated thua—A seated workman holds in the palm of his left band a flattish piece of sponge, lapped round his fore-finger. With the other hand, he places a slice of peel upon the sponge, the outer surface downwards, and presses the uppermost (zeste-) side, so as to give it a convex instead of concave surface. The oil vesicles are thus rup tured, and the oil which issues from them is absorbed by the sponge with which they are in contact. Each slice receives 4-5 squeezes, and is then thrown aside. The workman carefully avoids pressing the small bit of pulp attached to each slice. As the sponge becomes saturated, it is forcibly wrung out into a coarse earthenware bowl, provided with a spout, and of a size to hold at least 3 pints ; here the oil separates from the watery liquid accompanying it, and is decanted. Despite its apparent rudeness and wastefulness, this process is capable of affording an excellent article ; it is em ployed chiefly for treating lemons.
Another implement adopted with both lemon and bergamot is known as the ecuelle d piques. It is a .stout pewter saucer, about 87 in. wide, with a lip on one side for convenience of pouring. The bottom is covered with stout, sharp, brass pins, standing up about / in., the centre being deepened into a tube about I in. in diameter and 5 in. long, closed at the lower end. The whole resembles a shallow funnel, with the tube stopped up at the end. The peel is held in the hand, and rubbed over the pins, by which the oil-vessels of the entire surface are punctured ; the liberated oil flows down into the tube, which is emptied at intervals into another vessel, where the oil may separate from the turbid watery liquid accompanying it.
A modified form of the ecuelle, for extracting bergamot-oil from the full-grown, but unripe, entire fruits, is constructed as follows. The fruits are placed in a strong metallic dish, about 10 in. wide, having a raised central opening, forming with the outer edge a broad groove or channel, and covered with a lid of similar form. The inner surfaces of both dish and lid are provided with a number of
narrow, radiating, metallic ridge-blades, about / in. high, and resembling knife-backs. The dish is also perforated to permit the outflow of the oil, and both dish and lid are arranged in a metallic cylinder, placed over a vessel to receive the oil. By a simple set of cog-wheels, a handle causes the cover, which is very heavy, to revolve rapidly over the dish ; the fruit lying between the two is carried round, and simultaneously subjected to the action of the sharp ridges, which, rupturing the oil-vessels, set free the oil to flow out by the small holes in the bottom of the dish. Some 6-8 or more fruits are dealt with at once, and are kept under operation for about / minute; about 7000 fruits can thus be treated in one such machine per diem.
Distillation.—The oleiferous material is placed in an iron, copper, or glass still, of 1-1000 gal. capacity, and is covered with water ; superposed is a dome-shaped lid, terminating in a coil of pipe, placed in a vessel of cold water, and protruding therefrom with a tap at the end. On boiling the contents of the still, the essential oil passes over with the steam, and is condensed with it in the receiver ; the oil and water separate on standing. A great improvement, introduced by Drew, Heywood, and Barron, is the use of a steam-jacketed still, as shown in Fig. 1041. Steam is supplied from a boiler by the pipe a into the jacket b; within the head of the still, is fixed a "rouser "c, a double-branched stirrer curved to the form of the pan, and having a chain attached and made to drag over the bottom, the whole being set in motion by means of the handle d. The still is charged, and nearly filled with water ; the head is then bolted on, steam is admitted into the jacket, the contents are well stirred, and soon the oil and steam are carried up the pipe e, condensed in the refrigerator f, and let out at g into the receiver h. Here the oil and water separate, and escape by different taps. In the illustration, it is supposed that the oil obtained is heavier than water ; it will then sink, and be drawn out by the lower tap i, and, as soon as the water reaches the level of the upper tap k, it will flow into the syphon-funnel 1, and thence into the still. Thus the same water is repeatedly used in the still. The pipe m conveys cold water into the refrigerator f ; the water escapes as it becomes hot by the pipe n. When the oil distilled is lighter than water, the taps i k exchange duties. Before commencing operations, the siphon 1 is filled with water to prevent the escape of vapour.