136 PROCEEDINGS OF THE AMERICAN ACADEMY 



The formula requires : — 



1959 100.00 



The salt dissolves readily in alkaline hydrates. Its chief interest 

 lies in the fact that it serves to establish the existence of a 6-atom 

 series of arsenio-tungstates. 



Acid 6 : 4 Ammonium Salt. — When amnionic arsenate As0 4 NII 4 

 and neutral sodic tungstate are dissolved together, no precipitate is 

 formed at first, but after a short time a dense white crystalline salt is 

 thrown down, which after twelve hours becomes abundant. Boiling 

 water dissolves this salt readily, but it does not crystallize well from 

 the solution, forming only a thick white mass. If this mass be 

 dissolved in water, nitric acid added in excess gives a white crystalline 

 precipitate, but slightly soluble in the acid liquid and in water. Of 

 this salt, after washing with cold water, — 



0.8255 gr. gave 0.6013 gr. W0 3 = 72.84% 



1 .9486 gr. " 0.3980 gr. As.,O s Mg 2 (NH 4 ) 2 -f H 2 = 12.36 % As 2 0. 



1.2494 gr. « 0.2635 gr. NH 4 C1 =10.25% 



The analyses agree — though not very closely — with the formula 



6 W0 3 . As 2 5 . 4 (NH 4 ) 2 . 2 H 2 + 3 aq, 



which requires : — 



The differences are, I think, not greater than may be expected in 

 cases in which the salt analyzed cannot be purified by recrystalliza- 

 tion. 



Normal 16 : 6 Silver Salt. — I obtained this salt by the following 

 process : 100 gr. neutral sodic tungstate and 25 gr. arsenic acid were 

 dissolved together and the solution boiled for some time, then filtered 

 and evaporated upon a water-bath. After a day much sodic arsenate 

 separated in crystals. The filtrate from these crystals deposited a 



