258 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The analyses lead to the formula, 



4 M0O3 • 2 Pt02 . 2 (NH4)20 + 19 aq., 

 which requires : 



1439 100.00 



As in the last case the molybdic oxide is estimated by difference 

 which in the present state of our knowledge of analysis is the most 

 accurate method. The salt can hardly have been absolutely pure. 

 Water decomposes it and gives an opaque buff-yellow compound which 

 I have not examined. It will be seen from the above that the platino- 

 molybdates described do not correspond in general composition with the 

 only silico-molybdates known in which the ratio of molybdic to silicic 

 oxide is as 12:1, 



Rammelsberg * has described a molybdate of the dioxide and ammo- 

 nium which has the formula, 



4 M0O3 . 2 MoO., . (NH,).,0 + 9 aq. 



lu endeavoring to prepare a class of stanno-tungstates I obtained a 

 sodium salt the solution of which gave on evaporation a hard nearly 

 colorless glassy mass. This gave on analysis results which did not 

 correspond very well, but the mean of several led to the formula, 



4 WO,, . 2 SnOs . NaoO + 7 aq. 



The compound deserves further study, and is not without interest in 

 connection with the two salts noticed above. 



60 : 1 : 1 Platino-molybdate of Potassium. This salt was obtained 

 by boiling potassic molybdate with an excess of potassic hydrate, and 

 adding a solution of PtCl,;H2 ""til platinic hydrate which at first dis- 

 solves as fast as formed, was in small excess. Acetic acid was then 

 added to an acid reaction. On standing fine granular yellow crystals 

 were formed in quantity. These were dissolved in hot water and 

 recry stall i zed. Of this salt : 



0.5191 gram gave 0.0098 gram Pt = 2.20% PtOj. 

 0.5191 gram gave 0.5665 gram M0S3 = 81.85% M0O3. 



* Poggendoff, Annalen, CXXVII. 291. 



