In order to ascertain if the action of the amines was the same as that of salts of ammonia, I prepared the following compounds and tested their action on skins at 37° C., a control piece of the same skin being kept in water at the same temperature. The time in each case was one hour. All the solutions were neutral.
1. Ethylamine lactate: skin swells slightly, not “down” equal to puer.
2. Ethylamine propionate: skin moderately fallen, not equal to puer.
3. Ethylamine butyrate: about the same as Exp. 1.
4. Trimethylamine butyrate: very similar action to Exp. 3 and to ammonium butyrate.
The results correspond very closely with those obtained in previous experiments with various salts of ammonia (see Chapter [VI].), and justify us in assuming that in all essential respects the action is similar. The free amines enter into fresh combinations with acids which are produced by bacterial action, and this process goes on until all the nutrient material is exhausted.
The Role of Phosphates in the Bate.—There is no doubt that the phosphates in the bate play an important part, but exactly in what manner they act is not yet known. One of the principal effects is the part they play as “buffers,” in preventing brusque changes of the hydrion concentration during the bating process. This has been pointed out by Soerensen in the case of enzyme reactions. The phosphates in dung are mixtures, which are capable of fixing both acids and bases; and so the small quantities of these bodies, which are produced by the splitting up of the organic matter, are taken up or released as the case may be.
The chemistry of the phosphates is one of the most complicated branches of inorganic chemistry, and, as a consequence, the determination of the constitution of the various phosphates in dung is an extremely difficult matter, and demands a lengthy research. For instance, besides the salts directly derived from the three phosphoric acids, HPO3, H3PO4 and H4P2O7, phosphates exist which are probably derived from hypothetical di-, tri-, or meta-phosphoric acid, nHPO3, and a few salts have been isolated, which are perhaps derived from the hypothetical acids P4O7(OH)6 and P10O19(OH)12 (Watt’s Dict., art. “Phosphates”). Including the double salts, there are more than 16 different calcium salts of phosphoric acids. The normal lime salt Ca3(PO4)2 is very slightly soluble in water, but its solubility is increased by the presence of various organic substances such as exist in dung, and part of the soluble phosphates found in the bate are undoubtedly nothing more than this salt in solution. This fact has been utilized in the manufacture of the artificial bate Erodin (see Chapter [VII].).
The phosphoric acid in the puer is partly precipitated by the lime in the skins, and hence diminishes during the bating process. In some cases practically the whole of the phosphoric acid disappears from the solution.
The following experiment will give an idea of the amount of lime precipitated as phosphate. A filtered puer liquor was analysed for lime and phosphoric acid, before and after the skins were passed through. The results were, in grm. per litre—