326 Dr, Thomson on [May, 



the resulting compound will be nitric acid. I have tried the 

 experiments, which he describes, but find the results too varia- 

 ble to place any reliance on them. But it is not difficult to 

 demonstrate that nitric acid is in reality a compound of 100 

 volumes azotic and 250 volumes of oxygen gas. 



In the Annals of Fhilosophyy xvi. 334, I have shown by a 

 simple, but decisive experiment, that the atomic weight of nitric 

 acid is 6*75. The preceding observations leave no doubt that 

 the composition of protoxide of azote, deutoxide of azote, hypo- 

 nitrous acid, and nitrous acid, is as follows : 



Azote. Oxygen. 



Protoxide of azote 100 volumes + 50 volumes 



Deutoxide of azote 100 + 100 or 50 x 2 



Hyponitrous acid 100 + 150 or 60 x 3 



Nitrous acid 100 + 200 or 50 x 4 



We cannot avoid concluding, from observingthese proportions^ 

 that these different substances are composed as follows : 



Azote. Oxygen. 



Protoxide of azote 1 atom + 1 atom 



Deutoxide of azote 1 +2 



Hyponitrous acid .c 1 +3 



Nitrous acid 1 +4 



Consequently an atom of azote is represented by a volume of 

 azotic gas and an atom of oxygen by half a volume of oxygen 

 gas ; but the specific gravity of azotic gas is 0-9722, and that 

 of oxygen Mill, the half of which is 0o555 ; therefore, the 

 weight of an atom of oxygen is to that of an atom of azote as 

 0-5555 to 0-9722; but 5555 : 9722 :: 1 : 1-75; consequently, if 

 an atom of oxvgen be represented by 1, an atom of azote will 

 weigh 1*75. Substituting these weights for the atoms in the 

 preceding table, we obtain the atomic weights of these different 

 bodies as follows : 



Protoxide of azote 2*75 



Deutoxide of azote 3*75 



Hyponitrous acid 4*75 



Nitrous acid 5*75 



If to 5-75 we add another atom of oxygen, we obtain 6*75. 

 Now this is the weight of an atom of nitric acid. It cannot be 

 doubted, therefore, that nitric acid is a compound of five atoms 

 of oxygen and one atom of azote. But as an atom of azote 

 represents a volume, while an atom of oxygen represents half a 

 volume, it is evident that nitric acid must be a compound of 



