The extraction apparatus of Hänig and O. Reinhard is shown in Fig. 38. It can be turned over by means of cog-wheels. In the cover are an air valve, _e_, and safety valve, _f_; below the cover is a coil, _k_, fed with cold water from _c_. In the extraction, by opening the valve _v_, steam enters through _a_ at _l_; it is condensed by the cooled cover, the condensed water flows through the material on the sieve, and collects in the space B. After some time _v_ and _z_ are opened, the liquid is then boiled by the steam in the coil, _s_. Steam rises through the material, is condensed on the cover, and again drops down. At the end of the operation the solution is drawn off through the cock, _h_. [Illustration: FIG. 39.] =Kohlrausch’s Process for Obtaining Concentrated Extracts of Colouring Matters and Tannins.=—When dye-wood or tan-bark is continually brought in contact with fresh quantities of water, after some time it is exhausted; if the solution containing a certain quantity of the soluble matters is brought in contact with fresh material not yet extracted, it takes up more soluble matter, and thus becomes more concentrated. The substances contained in tan-bark are very soluble in water, so that by the appropriate treatment of a certain quantity of bark, divided amongst different vessels, with a certain quantity of water, on the one hand the bark can be exhausted completely, and on the other very concentrated solutions (”bark extracts”) obtained. The process patented by Kohlrausch is based upon the principles just stated; it can be used to obtain tannin extracts from tan-bark and colour extracts from dye-wood. In this process the raw materials need not be finely ground in order to be completely extracted; they may be used in large pieces. It will be understood from the following description that fine bark meal or finely-rasped dye-wood could not be worked. [Illustration: FIG. 40.] The apparatus consists of a number of 10 to 20 extractors connected together, also with a water tank above, and with a boiler. A single extractor is represented in section in Fig. 39, together with the necessary pipes and valves by which it is connected with the neighbouring extractors, the water tank and the boiler. Fig. 40 is a plan of three extractors connected together.