ISM.] On the Cause of Chemical Profm lions. 24? 



weight of the residue in the retort was 86-9; 87; 87'8; 88-8 

 in ditferent experiments. But the first experiment was made with 

 the greatest care. Accordiiig to it the tungstate ol" ammouia is 

 composed of 



Tungstic add 88-80 



Ammonia 5"(>3 



Water 557 



100-00 



The 5-57 of water contain 4*91 of oxygen, and the 5*63 of 

 ammonia contain 2-'t8. But 2 48 + 2 = 4-%". There are there- 

 fore two portions of water for one of ammonia, just as is the case 

 in the sulphate, Iiorate, and oxalate of ammonia. 100 parts of 

 acid are combined with G 34 of ammonia, wliich contain 2-914 of 

 oxygen. Now 2*914 x 6 = 17*484. We have seen that the 

 acid contains 19 H. Therefore this analysis siiows us that it must 

 contain G times as much oxygen as the base. And if we take^ the 

 mean of the results obtained ; that is to say, if we consider it as 

 most probable that tlie tungstate contains 87*8 of tungstic acid, 

 100 parts of that acid are neutralized by 7 parts of ammonia, 

 which contains 3'20-i of oxygen. And 3*206 x G= 19.236. 



I have stated that the residue in the retort after the decomposi- 

 tion of the tungstate was a blue powder. 1 cons'dcred it at first as 

 containing less oxygen than the acid ; but having treated 4 parts 

 of this oxide with smoking nitric acid without producing any alte- 

 ration on it, I exposed it to heat in a platinum crucible exactly 

 weighed. It changed colour the instant it began to get red hot, 

 and became straw yellow ; and I found that it had neither gained 

 nor lost weight. I repeated the experiment several times, and 

 always with the same result. On the other hand, when I heated to 

 redness the blue oxide in the retort in which it was formed, it did 

 not change its colour ; but if air was admitted, the portions that 

 came in contact with it assumed a yellow colour. The blue powder 

 dissolves in ammonia and in caustic potash, though more slowly 

 t!ian the ycllovv oxide. The solution is colourless, and 1 could not 

 find that it contained any thing else than tungstic acid. But what 

 Is tiie difference between these two states of tungstic acid ? How 

 docs tlie air contribute to change the blue colour into yellow? 

 When the yellow acid is very strongly heated it becomes green, 

 and at last blu(?lsh green. But it does not again recover its yellow 

 colour when exj)osed to a less temperature^ 



100 parts of nitrate of lead were dissolved in water, and preci- 

 pitated by a portion of the same tungstate of ammonia which liad 

 been found to contain 8H*H \w\- cent, of tungstic acid. I ob- 

 tained 235-.'j parts of timg^tate of lead. It constituted a yellowish 

 mass similar to pure tungstic acid. This salt is of course a com- 

 pound of 



