In India, the pods of the babool (_Acacia arabica_) are much used as a bate, the infusion being allowed to ferment. In their dry state they contain about 12 per cent. of an easily changeable tannin, which does not precipitate lime-water, and which by fermentation is very probably converted into gallic acid. The use of gallic acid itself as a bate has been patented by Albert Hull,[96] and would undoubtedly accomplish the removal of the lime if used in sufficient quantity; but as he only uses a solution of 25 mgr. per litre (one part in 40,000) any effect must be mainly due to the washing with water. Gallic acid forms dark oxidation products with lime. [96] Eng. Pat. 14,595, 1889. Of the fermentive methods of removing lime, “drenching” with fermenting bran-infusions is the simplest in theory, and has been very carefully investigated by Mr. J. T. Wood.[97] It will, therefore, be convenient to consider this process first, although it is frequently employed as a means of cleansing and slightly plumping the skin after the lime has been removed by puering or bating. In calf-kid manufacture, however, it is now used without previous puering, and in some other cases it is substituted for the use of dung bates. The most important of the active ferments are two species of bacteria, named by Wood _Bacterium furfuris_ α and β, which are very similar in their form and action (see L.I.L.B., p. 264), but produce a somewhat better fermentation together than separately. They are shown in Figs. 34 and 35. [97] Journ. Soc. Chem. Ind., 1890, p. 27; 1893, p. 422; 1897, p. 510; Brit. Assoc. Rep., 1893, p. 723. [Illustration: FIG. 34.--_Bacterium furfuris_ α.] [Illustration: FIG. 35.--_Bacterium furfuris_ β.] Neither species has any direct action on the hide substance, but ferments the glucose produced by the action of the cerealin of the bran on the starch which is present. A considerable quantity of hydrogen, with carbon dioxide, nitrogen and small quantities of hydrogen sulphide, are produced during the fermentation, together with lactic and acetic, and traces of formic and butyric acids and amines. Active drenches contain 1-3 grm. of mixed acids per liter, to which they owe their action, a perfectly satisfactory drenching being produced by an artificial drench containing 0·5 grm. of glacial acetic acid and 1 grm. of lactic acid (sp. gr. 1·210) per liter in which the skins were worked for 1¹⁄₂-2 hours, while 12-16 hours would have been required in the ordinary drench. An experimental drench gave the following results on analysis:-- Formic acid 0·0306 grm. per litre Acetic acid 0·2402 „ Butyric acid 0·0134 „ Lactic acid 0·7907 „ ------ Total 1·0749 „