Fig. 11.
Extraction being finished, the cock o is opened, and then the cock a, and the fluid allowed to run into the flask of the distilling apparatus ([Fig. 2]). For working on a large scale, the flask is, however, too small, and is suitably replaced by a bottle-shaped tin vessel, F (Fig. 11), the conical cover D of which is secured by means of the rubber ring R and iron screw-clamps, S. A bent glass tube fitted into the cover is connected with the cooling-pipe of the apparatus shown in [Fig. 2]. But the oils prepared by extraction are not sufficiently purified by mere rectification, as traces of the solvent adhere tenaciously to them, which can only be removed by passing a current of air through the oil. But contact with air has an injurious effect upon the delicacy of the odor. For expensive oils a current of air should therefore never be used, but one of pure carbonic acid. Fig. 12 shows a suitable apparatus for the purpose. The large bottle A, filled half full with pieces of white marble, is closed with a doubly-perforated cork; through one of the holes is inserted a funnel-tube, and through the other a short tube bent at a right angle. The latter is connected with another tube which reaches to the bottom of the vessel B, in which is also inserted a tube open in the bottom, and a short tube bent at a right angle. Alongside B stands another vessel, C, arranged in the same manner. The tube leading from C is connected with a tin pipe, D, with a rose-like expansion on its lower end. This pipe is inserted in the glass balloon containing the volatile oil. Finally, a pipe leads to the flask F, filled with water.
Fig. 12.
To put the apparatus in operation, strongly diluted hydrochloric acid is poured through the funnel-tube upon the pieces of marble in A, which causes the development of a current of carbonic acid. But as the latter carries along water and hydrochloric acid, it has to be freed from them before coming in contact with the volatile oil. The vessels B and C serve for the purpose. B is half filled with water, while C contains strong sulphuric acid. In B the hydrochloric acid carried along with the current of carbonic acid is retained, while the water is fixed on the sulphuric acid in C. The current of carbonic acid passing out from C is perfectly pure, and enters the volatile oil through the fine perforations in the pipe D. It absorbs the traces of solvent still adhering to the oil, and finally passes out through the water in the bottle F.
Volatile oils obtained by extraction, and purified by a current of carbonic acid, will keep for years without undergoing alteration, if placed immediately in hermetically closed vessels and stored in a dark place. Oils purified by a current of air always become somewhat thickly fluid by storing, and partially lose their fine odor, which is due to the oxygen absorbed during the process.
For the extraction of oil on a larger scale, the apparatus shown in Fig. 13 is very suitable. It consists of two principal parts, the actual extracting vessel E, and the still B. The extracting vessel E sits in a vat containing cold water, W, the arrangement being such that the heated water can be removed and replaced by cold. The still B sits in a boiler, K, filled with hot water.
The apparatus is charged as follows: The conical head C of the extracting vessel E is unscrewed and its connection at H with the pipe R loosened. The extracting vessel is then charged with the vegetable substance, the head C replaced, and the connection with the pipe R restored. The cocks H2 and H4 are then opened, and the required quantity of solvent is brought into the still. Both cocks are then closed, and the cocks H and H1 opened. The water in the boiler is then heated until the contents of the still commence to boil. The vapor of the solvent ascends through the pipe R; on entering the extracting vessel E it is condensed, and after falling as a spray upon the material to be extracted, finally returns impregnated with volatile oil to the still B. Here the solvent is revaporized, and passes again through the material in the extracting vessel, while the extracted oil remains in the still. During the boiling of the solvent the extracting vessel must be suitably cooled by the constant admission of cold water.
Fig. 13.