68 PROCEEDINGS OF THE AMERICAN ACADEMY 



24 : 3 Ammom'c Phospho-molyhdate. — The constitution of the beau- 

 tiful yellow salt which is formed when an excess of a mineral acid is 

 added to a solution containing molybdic and jDhosphoric oxides and a 

 salt of ammonium, has long been in dispute. The analyses of Svan- 

 berg and Struve,* Nutzinger,t Sonnenschein,t Lipowitz,§ and Selig- 

 sohn,|| gave results which differed very sensibly from each other, 

 according to the method of analysis employed. Debray gave the 

 formula 



20 M0O3 . P2O5 . 3 (NIIJP 4- 3 aq, 



but without the details of his analysis. More recently the subject has 

 been examined with great care by Finkener,1[ who has arrived at the 

 conclusion that, though the percentages of water and ammonia may vary 

 within wide limits, the ratio of the molybdic and phosphoric oxides is 

 always as 24 : 1. 



With respect to the preparation and properties of the yellow ammo- 

 nium salt, I have little to add to what has been done by these chemists. 

 I repeatedly prepared the salt for analysis, usually by mixing solutions 

 of ammonic molybdate — 7:3 salt — and phosphate, adding nitric acid 

 in excess to the solution, and boiling. When the mixed solution is 

 boiled for a short time, the precipitation of the yellow salt is complete 

 after standing until the liquid becomes cold. In the publication of this 

 result, which is important in analysis, I hav^ been anticipated by Atter- 

 berg ; ** but I propose in another paper to give the results of my work 

 on the quantitative determination of phosphoric acid, and will then give 

 ample details. 



As regards the composition of the yellow phospho-molybdates of 

 ammonium, my results do not agree with those of Finkener, as I think 

 I have evidence that, as in the case of the phospho-tungstates, there 

 are series of phospho-molybdates in which the ratio of the molybdic to 

 the phosphoric oxide is as 20 : 1, as 22 : 1, and as 24 : 1. In one prepa- 

 ration, — 



1.1492 gr. lost on ignition with W04Na2 0.0827 gr. NH3 and H^ 

 = 7.20% 



* Journal fiir prakt. Cheniie, xliv. 291. 

 t Pliarmaccut. Vierteljahresschrift, iv. 549. 

 \ Journal fiir prakt. Cliemie, liii. 342. 

 § PoggenJorff's Annalen, cix. 1.35. 

 II Journal fiir prakt. Cheniie, Ixvii. 470. 

 1" Loc cit. 

 ** Berichte der Cliem. Gesellschaft, 1881, p. 1217. 



