The solutions of the essential oils in bisulphide of carbon are distilled off in the steam still illustrated in Fig. 27; the steam enters at _h_, the water of condensation escapes at _d_, the liquid to be distilled enters at _e_ from a container at a higher level. The boiling is kept uniform by the stirring arrangement _hg_. After the bisulphide of carbon is distilled off, air is passed through the oil by the curved tube _a_ which has fine perforations, so as to evaporate the last traces of the solvent. In Vohl’s apparatus (Fig. 28), arranged for petroleum ether, the extraction is effected with the boiling fluid; hence this apparatus is better adapted for the cheaper oils than for the finest oils from flowers. The apparatus consists of two extractors A A, the accumulator B, and the condenser C. Petroleum ether is allowed to flow over the substances to be extracted, by opening the faucets _mm_, _vh_, closing _ogw_E, and opening _o_, the course being through _ux_ to B. When B is two-thirds full, the flow of petroleum ether is cut off, steam is admitted through _y_ and the contents of B are brought to the boiling-point. The vapors pass through _g_ and are condensed in _f_ until the contents of A reach the boiling-point of the solvent, when the vapors pass through _i_ into C, and after closing _m´_ the liquid passes through _ml_ into the inner cylinder of the extraction apparatus and returns through _uxx_. After the contents of A are extracted, _m´_ is opened, _m_ closed, and steam is admitted through _d_ into the jacket of A; the vapors of the solvent force the liquid part of the contents through _ux_ into B. Overfilling of B is prevented by allowing the vapors of the solvent to escape at the proper time into the condenser through _p_ by opening _q_. Then _v_ is closed, _q_ opened, and the steam present in A drawn off by an exhaust applied to _p_; as soon as _p_ begins to cool, all the petroleum ether is distilled off, the steam is cut off at _d_, and the extract evacuated through _t_. The contents of B are brought into a still through D and E. [Illustration: FIG. 29.] By employing greater pressure the extraction can also be effected by what is called displacement; the material to be extracted is placed in a stout-walled vessel S (Fig. 29) which is connected by a narrow tube at least ten yards long with the vessel F containing the solvent. Stopcock H is first opened, then stop-cock H_{1} which is closed as soon as fluid begins to flow from it. After the liquid has remained in contact with the material for from thirty to sixty minutes, H_{1} is opened very slowly, the liquid is allowed to escape and is displaced with water which is made to pass out of F in the same way as the solvent, until the latter is completely displaced from S.