Fixed oils are best extracted in so-called drop presses, the material having first been comminuted between rollers. These are arranged as shown in section in Fig. 5, and in ground plan in Fig. 6. The apparatus consists of two smooth or slightly grooved iron cylinders A and B, respectively four feet and one foot in diameter, which can be approximated or separated by means of set screws. The material is placed into the trough F containing a feeding roller moved by the belt P. The scrapers FF, pressed against the cylinders by means of weighted levers, free the rollers from adhering pieces. The drop presses Figs. 7 and 8 consist of a hydraulic press with cylinders A and piston B; the troughs E are movable by means of rings between two vertical columns and every trough has a circular gutter _d_ for the reception of the expressed oil. The iron pots G have double walls, the inner of which has a series of openings at its upper part; these pots are filled with the bruised material to be pressed and after this has been covered with a plate of horse-hair tissue are set in the press. [Illustration: FIG. 7.] [Illustration: FIG. 8.] As the piston rises, the troughs E sink into the pots, the escaping oil collects in the gutters _d_ and thence passes into a receptacle. After pressing, the piston is allowed to sink back, the pots G are drawn aside (Fig. 8) to tabular surfaces, and other pots are substituted for the exhausted ones. These drop presses are suitable for the extraction of all fixed oils and also volatile oils present in orange and lemon peel, etc. DISTILLATION. Many odors or essential oils possess the remarkable property that their vapors pass so largely with that of boiling water that they can be extracted in this way (by “distillation”) from vegetable substances, though the essential oils have a boiling-point far above that of water. Distillation can be employed for a large number of substances; for instance, the essential oils present in cumin, anise, lavender, fennel, mace, nutmeg, etc., are extracted exclusively in this manner. [Illustration: FIG. 9.] For the extraction of odors in this way, according to the quantities of material to be worked, different apparatuses are used, some of the most important of which will be here described. For manufacturers who run without steam and are obliged to use a naked flame, the adjoining apparatus (Fig. 9) will be advantageous.