AZOTIC GAS. 109 



And the proportion of azotic gas was always 

 found to increase with the length of the process. 

 I came nearer the truth with a small quantity of 

 nitre than with a large quanity but I was never 

 able to obtain the whole volume of gas which 

 nitre is capable of giving out. 



I next tried to decompose nitre by heating it, By char- 

 mixed with charcoal powder, in a copper tube. c 

 The tube was heated to redness, and the gaseous 

 products collected over mercury. By this pro- 

 cess, I obtained a greater volume of gas than 

 nitre itself is capable of giving out ; in some 

 cases, the volumes of the azotic gas and carbonic 

 acid gas, evolved, were to each other as fol- 

 lows : 



1 volume azotic 



2^ volumes carbonic acid. 



But in general, the gas, unabsorbable by potash, 

 bore a greater ratio to the carbonic acid gas than 

 the preceding ; and the longer the heat was con- 

 tinued, the greater was the quantity of unab- 

 sorbable gas evolved. There was always evolved, 

 likewise, a very considerable quantity of water. 

 It was impossible to doubt, that the charcoal 

 (though I had previously heated it strongly in a 

 wind furnace) contained both oxygen and hy- 

 drogen ; and, when I substituted Kilkenny coal 

 for charcoal, my results were not more satisfac- 

 tory. With Kilkenny coal, the proportion of 



