Manganese as the Pyrophosphate. 235 



The conversion of a molecule of tri manganous phosphate to 

 the ammonium manganese phosphate might be due, conceiva- 

 bly, either to the action of free ammonia or to the action of a 

 salt of ammonium. The action of ammonia could only take 

 place at the expense of a partial loss of manganese from the 

 phosphate and its appearance as a hydroxide, two-thirds of the 

 manganese going into two molecules of the ammonium man- 

 ganese phosphate. In the presence of ammonium salts it is pos- 

 sible that the manganese oxide thus replaced might enter into 

 union with the acid radical of the ammonium salt setting free 

 ammonia ; but if the ammonium salt present were the phos- 

 phate, or if an alkaline phosphate were present with other 

 suitable ammonium salts, it is conceivable that the replaced 

 manganese might appear as a constituent of a third molecule 

 of ammonium manganese phosphate. In any event, it would 

 be the ammonium salt and not the free ammonia which would 

 determine the formation of the third molecule of the ammo- 

 nium manganese phosphate. Plainly, too, the ammonium salt 

 by itself, if it were a phosphate, or if a soluble phosphate were 

 also present, might accomplish the conversion without the 

 intermediate action of free ammonia. Unless, therefore, free 

 ammonia favors the insolubility of the ammonium manganese 

 phosphate, its presence would be unnecessary and might even 

 be an actual disadvantage if the hydroxide naturally formed by 

 its action upon the manganese phosphate were to fail to reunite 

 fully with a phosphoric acid radical. It is plain, too, that 

 the action of free ammonia might not stop with the replace- 

 ment of one out of the three of the manganese atoms present 

 in the molecule, but might even proceed under favorable con- 

 ditions to the formation of phosphate richer in ammonium and to 

 the separation of more manganese from its union with the acid 

 radical. As a matter of fact Munroe* has shown that the pro- 

 longed action of hot ammonia upon the precipitate produced by 

 the interaction of a manganous salt and an alkaline phosphate 

 does actually produce a hydroxide which blackens as it takes 

 oxygen from the air. Our attention has been given, therefore, 

 more especially to a study of the conditions of action under 

 which a salt of ammonium — the chloride — may bring about the 

 conversion of the precipitate first thrown down by an alkaline 

 phosphate to the form of the ammonium manganese phosphate. 

 Experiments were made upon solutions of pure manganous 

 chloride prepared and standardized by means of the sulphate 

 method, as described in a former paper,f to show the effect of 

 varying amounts of ammonium chloride on the condition of the 

 precipitate and upon the solubility of the precipitate when 



* Amer. Chemist, 1ST 7. f This Jour. IV, v, 209. 



