Professor H. R. PROCTER, in his “Principles of Leather Manufacture,” 1903, p. 153, has given a very complete account of chemical deliming, and also of the bating and puering processes. Meunier and Vaney, “La Tannerie,” 1903, give a general review of our knowledge of these processes up to that date. These accounts are extremely useful, but treat the subject in a general manner. I propose to treat of the particular case of puering by means of an infusion of dogs’ dung in water, as I believe this will give an insight into all the other bating processes. So far as the purely chemical action of the bate goes, it consists in the solution of the lime contained in the skins,[18] thus setting free a certain portion of skin substance which was combined with the lime, and the subsequent solution of more or less of this skin substance. [18] Limed sheep grains, or Pelts, which have been limed for splitting, contain from 3 per cent. to 6 per cent. CaO on the dry skin (see footnote, p. 7), and about 80 per cent. of water. In a typical case of a fully limed grain, the lime was found to be distributed as follows:-- Free uncombined lime (CaO) 1·7 per cent. on the dry skin CaO combined with skin 2·5 " CaO as carbonate, or other salts 1·4 " ----- 5·6 Thus, 75 per cent. of the total lime in the skin was in the caustic state. If the skin be cut during the progress of the bating operation, and a solution of phenolphthalein applied to the cut surface, the course of bating may be followed, and it will be found that the caustic lime disappears from the skin in a very short period of time, accompanied by the sudden collapse of the fibres. We shall treat of this more fully in Chapter III. After puering, the lime (CaO) contained in the skin, amounts to 0·5 to 0·9 per cent., calculated on the dry skin. This lime is in a perfectly neutral state, and is more or less in combination with the fibre of the skin. The exact state in which the lime exists in the skin _after_ puering is not known, and would form a very interesting subject for research. If a fresh puer be made and boiled for half an hour, then allowed to cool to 95° F., it will be found to remove the lime from the skin in a very similar way to an ordinary bate, but it has not so rapid a reducing action as an unboiled bate. In this case both bacteria and enzymes are destroyed, so that the action may be put down to the chemical constituents of the bate. *Chemical Composition of the Puer.*--The mineral constituents of the fæces, both in dogs and human beings, are well known, owing to the study of the processes of digestion and nutrition in physiological laboratories; but the organic constituents are yet little known, and the sum of the weight of those at present estimated is far from the total of these matters present.