As a rule we employ either petroleum ether or bisulphide of carbon (see above, pp. 65, 66) because these products are cheaper than ether or chloroform. The apparatus we use for this purpose is illustrated in Fig. 21. It consists of a cylinder C made of tinned iron, which is provided above with a circular gutter R terminating in a stop-cock _h_ and which can be closed by a lid D bearing a stop-cock _o_. A tube _b_ with a stop-cock _a_ enters the bottom of the cylinder. The latter is filled with the flowers, the volatile liquid (petroleum ether, bisulphide of carbon, etc.) is poured over them, the lid is put on, and the gutter R filled with water, thereby sealing the contents of the vessel hermetically. After the extraction, which requires about thirty to forty minutes, stop-cock _o_ is opened first, then stop-cock _a_, and the liquid is allowed to escape into the retort of the still (Fig. 12). If the extraction is to be repeated, the water is allowed to escape from the gutter through _h_, the lid is opened, and the solvent is again poured over the flowers. For operation on a larger scale the glass retorts are too small and should be replaced by tin vessels (Fig. 22) having the form of a wide-mouthed bottle F; they are closed by a lid D which is rendered air tight by being clamped upon the flange of the vessel (R) with iron screws S, a pasteboard washer being interposed; a curved glass tube connects the apparatus with the condenser of Fig. 12. [Illustration: FIG. 21.] [Illustration: FIG. 22.] The solutions of the aromatic substances are evaporated in these apparatuses at the lowest possible temperature, the solvent being condensed and used over again. The heat required is for ether about 36° C. (97° F.), for chloroform about 65° C. (149° F.), for petroleum ether about 56° C. (133° F.), and for bisulphide of carbon about 45° C. (113° F.). If it is desired to obtain the aromatic substances pure from an alcoholic extract of the pomades made by one of the above-described processes—which is rarely done since these solutions are generally used as such for perfumes—a heat of 75 to 80 C. (167 to 176° F.) is required. Another extraction apparatus illustrated in Fig. 23 is well adapted to operations on a large scale. Its main parts are the extractor E and the still B. The former is set in a vat W continually supplied with cold water. The still B is surrounded with hot water in the boiler K. To start the apparatus the cone C is removed, the vessel E is filled with the material to be extracted, and C is replaced. The faucets H_{2} and H_{4} are opened, the solvent is poured into the still through the latter, when these faucets are closed and those marked H and H_{1} are opened. [Illustration: FIG. 23.]