In addition to this, a considerable amount of lime is removed from the skins which is not found afterwards in solution, but which is precipitated in an insoluble form during the course of the bating process. In an experiment to determine the amount of this insoluble lime, the following figures were obtained:-- LIME IN PUER LIQUOR, GRAMS PER LITRE CaO. Before Skins After Skins Soluble lime 0·19 0·485 Insoluble lime 0·13 0·485 ---- ----- 0·32 0·970 It will be noted that the amount of insoluble lime has increased to a greater extent than the soluble lime, showing that part of the lime from the skins has been precipitated in an insoluble form. The increase of lime in the solution is 0·295 grm. per litre of soluble lime, and 0·355 grm. per litre of insoluble lime, a total increase of 0·650 grm.; that is, the ratio of soluble lime to insoluble lime in the original puer is 1·46 : 1. In the used puer it is 1 : 1, so that in the above case more than half the lime removed from the skins (54·5 per cent.) has been precipitated in an insoluble form, some of it in the form of calcium phosphate, and the remainder probably in the form of calcium oxalate. Crystals of calcium oxalate may be seen under the microscope in the puer residues. The oxalic acid is produced by bacterial action, as has been shown by Zopf[31] and Banning[32]; but it is difficult to estimate it in the bate, and a reliable analytical method of doing so requires devising. [31] Ber. Deutsch. Botan. Ges. 1900, xviii. 32, J.S.C.I. 1900, 386. [32] Centr. Bakt. Parasitenk, ii. Abt. viii., 393, etc., J.S.C.I. 1902, 1151. A further 30 per cent. to 40 per cent. of the lime in the skins is removed by the chemical action of the complex amines of the organic acids, and by the mechanical effect of the paddle or drum, so that the final result is more or less as follows:-- Per cent. Lime neutralized by free acids 9 Lime dissolved by complex amines 25 Lime precipitated 30 Lime remaining in the skins 36 --- 100 The lime remaining in the skins is not in the caustic state, but principally in the form of neutral salts (see footnote to p. 24). [Illustration: Fig. 7.]