NITROGEN. 



361 



yields no smoke, nor docs it foul a gun. Gun-cotton, when dissolved in ether 

 gives us collodion for photographic purposes. 



In speaking farther of the compounds of nitrogen with oxygen ; we will 

 limit ourselves to the monoxide, or laughing gas. This is now used as an 

 anaesthetic in dentistry, etc., and is quite successful, as a rule. People 



Fig. 352. Nitric acid obtained from nitre and sulphuric acid. 



afflicted with heart disease should not use it without advice, however. 

 When inhaled into the lungs it makes the subject very hilarious, and the 



Fig. 353. Cavendish's experiment. 



effect is rather noisy. It is obtained from the nitrate of ammonia, which, on 

 the application of heat, decomposes into nitrous oxide and vapour. Warm 

 water should be used for the trough. The gas is a powerful supporter of 

 combustion. 



Binoxide of nitrogen is of importance in the manufacture of sulphuric 

 acid. 



