A more detailed description of the different parts of the apparatus can be seen by consulting Figs. 19, 20, and 21. In A, Fig. 19, is represented a section of the flask which holds the solvent, showing how the sides of the hood containing the matters to be extracted pass over the neck of the flask, and showing at S a small siphon inserted in the space between the neck of the flask and the walls of the hood for the purpose of removing any solvent that may accumulate in this space. A view of the flask itself is shown at Aʹ. It is made by taking an ordinary flask, softening it about the neck and pressing the neck in so as to form a cup, as indicated at Aʹ, to hold the mercury which seals the union of the flask with the condenser. The flask is held in position by passing a rubber band below it, which is attached to two glass nipples, _b_, blown onto the containing vessel, as shown in Fig. 18. The material to be extracted may be contained in an ordinary tube, as shown in Fig. 20, which may be made from a test tube drawn out, as indicated in the figure, having a perforated platinum disk sealed in at D. The containing tube rests upon the edges of the flask containing the solvent by means of nipples shown at _t_. If a siphon tube is to be used, one of the most convenient forms is shown in Fig. 21, in which the siphon lies entirely within the extracting tube, thus being protected from breakage. By means of this apparatus the extractions can be carried on with a very small quantity of solvent, there being scarcely any leakage, even with the most volatile solvents, such as ether and petroleum. The apparatus is always ready for use, no corks are to be extracted, and no ground glass joints to be fitted. =40. Soxhlet’s Extraction Apparatus.=—A form of continuous extraction apparatus has been proposed by Soxhlet which permits the passage of the vapors of the solvent into the condenser by a separate tube and the return of the condensed solvent after having stood in contact with the sample, to the evaporating flask by a siphon. The advantage of this process lies in freeing the sample entirely from the rise of temperature due to contact with the vapors of the solvent, and in the second place in the complete saturation of the sample with the solvent before siphoning. The sample is conveniently held in a cylinder of extracted filter-paper open above and closed below. This is placed in the large tube between the evaporating flask and the condenser. The sample should not fill the paper holder, and if disposed to float in the solvent, should be held down with a plug of asbestos fiber or of glass wool. The extract may be transferred, by dissolving in the solvent, from the flask to a drying dish, or it may be dried and weighed in the flask where first received. [Illustration: FIGURE 22. SOXHLET EXTRACTION APPARATUS.]