OF ARTS AND SCIENCES. 79 



The analyses lead to the formula 



10 MoO, . 2 P 2 5 . 5 (NH 4 ) 2 . H 2 -f G aq, 

 or 



5 MoO s . P,0., • 3 (NH 4 ) 2 + 5 Mo0 3 . P 2 0. . 2 (NH 4 ) 2 . H 2 + G aq, 



which requires : — 



The phosphoric oxide was determined by double precipitation only, 

 without subsequent treatment with ammonic sulphide. The percent- 

 age is a little lower than that required by the formula, which is 

 unusual ; but the general agreement of the analyses with the formula 

 is satisfactory. Rammelsberg has described an acid potassium salt 

 with the formula 



10 MoO, . P L) 0,, • 5 K 2 . H 2 -f 19 aq. 

 It is therefore at least probable that we shall find another ammonia 

 salt with 20 atoms of water, and another potassium salt with 7 atoms. 

 Zenker has described another potassic salt to which he gives the 

 formula, — as I should write it, — 



9 M0O3 . P 2 5 • 4 K P • 2 H 2 + 18 aq ; 



but the results of his analyses differ very widely from the percentages 

 required by the formula, and on repeating his process I obtained 

 only the 10:5 atom salt of Rammelsberg. The formula given above 

 for this salt requires 11.11 % P 2 5 - I founu H.22%. 



Rammelsberg * has also described a white insoluble potassium salt 

 to which he gives the formula 15 MoO, . P 2 5 ■ ^ K 2 0, but without any 

 statement of his analyses. 



ARSENIO-MOLYBDATES. 



Compounds of arsenic and molybdic oxides have been described 

 by Seyberth f and by Debray.J Sey berth obtained an acid with the 

 formula, — as I should write it, — 



* Loc. cit. 



t Berichte der Cliem. Gesellschaft, 1874, p. 391. 



% Comptes Rendus, lxxviii. 1408. 



