These figures were obtained by the ordinary colorimetric method described on p. [32].
Adding together the alkalinity of the bate run away, and the acidity of the new bate which is neutralized, the total for 1 and 2 = 38 c.c. N/1 acid, and for 3 and 4, 51 c.c. N/1 acid.
Multiplying by 810 (volume of bate less volume of dry skin), we find that the skins have neutralized 30·78 and 41·31 litres N/1 acid respectively. Since one litre of N/1 acid will neutralize 28 grm. of lime, it follows that the lime removed by the bate was in one case 862 grm., in the other case 1157 grm.
The 500 kilos, of wet washed grains introduced into the paddle contain approximately 0·5 per cent. of lime CaO, equivalent to 2500 grm. altogether. As will be seen from the figures given in table, p. [35], the free acids present in the fresh bate are only capable of neutralizing 10 × 810 c.c. of normal alkali, and this is equivalent to 225 grm. of CaO, or 9 per cent. of the total lime.[30]
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.