=39. Knorr’s Extraction Apparatus.=—The apparatus which has been chiefly used in this laboratory for the past few years is shown in the accompanying figure.[18] The principle of the construction of the apparatus lies in the complete suppression of stoppers and in sealing the only joint of the device with mercury. The construction and operation of the apparatus will be understood by a brief description of its parts. A is the flask containing the solvent, W a steam bath made by cutting off the top of a bottle, inverting it and conducting the steam into one of the tubes shown in the stopper while the condensed water runs out of the other. The top of the bath is covered with a number of concentric copper rings, so that the opening may be made of any desirable size. B represents the condenser, which is a long glass tube on which a number of bulbs has been blown, and which is attached to the hood for holding the material to be extracted, as represented at Bʹ, making a solid glass union. Before joining the tube at Bʹ the rubber stopper which is to hold it into the outside condenser of B is slipped on, or the rubber stopper may be cut into its center and slipped over the tube after the union is made. In case alcohol is to be used for the solvent, requiring a higher temperature, the flask holding the solvent is placed entirely within the steam-bath, as represented at Aʹ. [Illustration: FIGURE 18. KNORR’S EXTRACTION APPARATUS.] [Illustration: FIGURE 19. EXTRACTION FLASK.] [Illustration: FIGURE 20. EXTRACTION TUBE.] [Illustration: FIGURE 21. EXTRACTION SIPHON TUBE.]