AZOTIC GAS. 113 



Nitric acid is the compound of azote and oxy- 

 gen, which contains the maximum quantity of 

 oxygen. It is obtained by heating a mixture of Method of 

 sulphuric acid and nitre, in a retort, to which 

 receiver is luted. When 6 parts of the strong- 

 est sulphuric acid of commerce are mixed with 

 12f parts of nitre, thoroughly freed from water, 

 and perfectly pure, the acid which comes over 

 is the strongest that can be procured. Its speci- 

 fic gravity is about 1-55, and it is a compound of 

 1 atom acid and 1 atom water, or it contains 



Real acid 8 



Water 14-286 parts 



100-000 



When 12i parts of sulphuric acid are mixed with 

 12f parts of pure anhydrous nitre, the whole ni- 

 tric acid may be obtained without any loss ; but 

 its specific gravity is only 1-4855, and it is a 

 compound of 1 atom real acid, arid 2 atoms 

 water. 



When nitric acid is quite free from nitrous 

 gas, it is colourless, and nearly as limpid as wa- 

 ter ; but the presence of this gas gives it a yellow, 

 a red, or a brown colour, according to its quan- 

 tity. This gas greatly increases the volatility of 

 the acid, but its effect upon the specific gravity 

 is not so great as I had anticipated the volume 

 of the acid being increased, nearly in proportion 

 to the quantity of gas absorbed. 



VOL. I. H 



