1820.] Scientific Intelligence. 225- 



Protoxide of azote 100 volumes 



Hydrogen 100 



After the combustion there will remain a quantity of azote 

 making 100 volumes. Now 100 volumes of hydrogen for com- 

 plete combustion require 50 volumes of oxygen. From this it is 

 obvious that 100 volumes of protoxide of azote are composed of 



Azotic gas 100 volumes 



Oxygen gas 50 



condensed into 100 volumes ; or, which is the same thing, of 

 one volume of azote and half a volume of oxygen condensed into 

 one volume. Hence we must obtain its specific gravity by adding 

 half the specific gravity of oxygen gas to the specific gravity of 



azotic gas. 



Specific gravity of azote 0'9722 



Half specific gravity of oxygen 0*5565 



Specific gravity of protoxide of azote = 1-5277 



Now Colin found the specific gravity of this gas 1*5204, and 

 a careful set of experiments made in my laboratory gave the 

 specific gravity of this gas 1*5269 — a number which is much less 

 than . , (j'oo th part from the theoretical number. There seems 

 then no reason to doubt the accuracy of the opinion, that this 

 gas is a compound of a volume of azotic gas and half a volume 

 of oxygen gas condensed into one volume. 



Azote. Oxygen. 



Nitrous gas is formed of 1 vol. + 1 vol. constituting 2 vols. 

 Protoxide of azote ....1 +-i 1 



There seems no reason, therefore, to doubt that if nitrous gas 

 could be deprived of half its oxygen, it would be converted into 

 protoxide of azote, and that, by this abstraction, its bulk would 

 be reduced exactly one half. But upon putting this apparently 

 accurate conclusion to the test of experiment, the result turns 

 out considerably different from what would be expected. 



Every chemist is aware of the fact that nitrous gas is converted 

 into protoxide of azote by keeping in it a quantity of moistened 

 iron wire. The fact was first observed by Dr. Priestley, and led 

 to the original discovery of protoxide of azote. The experiment 

 must have been very often repeated since, though 1 am not 

 aware that any very precise trials have been made to determine 

 the change of bulk which takes place. It may be worth while, 

 therefore, to relate here the result of a very careful experiment 

 which I made to determine this point. 



Fifteen cubic inches of nitrous gas (containing one per cent, of 

 azotic gas) were let up into a glass jar standing over mercury, and 

 previously filled with that liquid. The barometer stood at 29*08- 



Vol. XV. N^ III. P 



