| Before | After | |
| Soluble lime as CaO | 0·364 | 0·540 |
| P2O5 | 0·424 | 0·328 |
Increase of lime, 0·176 grm.; diminution of P2O5, 0·096 grm. Calculated to calcium phosphate Ca3(PO4)2, this amount of phosphoric acid has combined with 0·114 grm. CaO. Assuming that the ratio of soluble to insoluble lime is the same as given, p. [36], then the lime is distributed as follows:—
| Grm. | ||
| Increase of soluble CaO | 0·176 | |
| " " insol. CaO | 0·210 | |
| Lime as Ca3(PO4)2 | 0·114 | |
| Hence | " " oxalate (?) | 0·096 |
That is, of the lime precipitated, 54 per cent. is phosphate, 46 per cent. oxalate.
In another puer containing before use 0·383 grm. P2O5 per litre, only traces of phosphates were found in solution after goods had been puered in the liquor, and in some analyses by Jean ([39]) the following figures were obtained:—
Grams of Phosphoric Acid per Litre.
| Fresh dung after four days’ maceration | 0·082 |
| Bate after one pack of skins | 0·036 |
| Bate after two packs of skins | 0·018 |
Although these figures are less than those found at Trent Bridge, they confirm the fact that the soluble phosphates diminish during the bating process.
The phosphates in solution thus diminish during the bating, and are found in the insoluble matter which separates out. A small portion of the lime remaining in the skins is also converted into phosphate by the action of the bate. In an experiment to determine this, a portion of the same skin was taken before and after puering. The pieces were dried, ashed, the ash dissolved in dilute nitric acid, and the phosphates precipitated by ammonium molybdate. In the skin before puering no phosphates were present, but in the skin after puering there was a small amount, though not sufficient to weigh.
The action of ammonium phosphate on the lime in the skin is very small. A skin was treated with a 0·1 per cent. solution of ammonium phosphate at 100° F. for one hour. The CaO in the dry skin was estimated, and found to be—