_Preparation of the infusions._--Extracts are dissolved in hot water, and if necessary, filtered. Barks and other solid materials are treated in Prof. von Schroeder's extraction-apparatus (Fig. 20) (which seems very well adapted for its purpose). This consists of a perfectly cylindrical vessel of cast-tin, about 12·5 _c.m._ deep and 7 _c.m._ diameter. A strainer covered with fine muslin fits it like a piston.[Q] The powdered material is placed in the cylinder, and stirred up with 200 _c.c._ of cold water. At the end of an hour, the piston is inserted and pressed down gently, the clear liquor is poured off, and the process is 4 times repeated with hot water, at intervals of 1/2 hour, placing the cylinder in a water-bath. The liquid is made up to 1 _litre_, and, if necessary, filtered (Report, p. 66). The quantity of material used should be such as to give an infusion of which 10 _c.c._ do not reduce more than 8 _c.c._ permanganate. If it is desired to determine separately the "easily soluble tannin" (viz. that extracted by cold water), Real's Press (Fig. 21) is employed, which consists of a cylinder _a_, through which water may be forced by the pressure of a column of liquid. The small sieve _d_, covered with a disc of linen, is placed in _a_, next the tanning material previously thoroughly moistened with water, and the tap is closed. The press is then filled with water and left 15 hours under a pressure of 1-1/2 _metres_. The tap is then opened and 1 _litre_ is allowed to run through in the course of about 2 hours, and mixed by shaking. The material is finally exhausted like a new material in von Schroeder's apparatus to extract the difficultly soluble tannin. [Footnote Q: Both this apparatus, and the Real's press, may be obtained from C. Focke, Zinngiesser, Grosse Kirchgasse 3, Dresden.] [Illustration: Fig. 21.] The titration is carried out as before described; in each infusion separately to determine the "not-tannin" 50 _c.c._ are treated with 3 _grm._ hide-powder, and 10 _c.c._ are titrated. It may be well in conclusion for the writer to state for the information of the non-chemical reader, that though for purposes of comparison of the results of different chemists, it is most desirable to have a standard method of the highest possible perfection; any of the accepted modifications of the Löwenthal method will give excellent practical results in careful hands. CHAPTER VII. SOLE-LEATHER:--Preparing the Hides. The principal sources of hides for sole-leather are:--