v THE STUDY OF GASES 79 



air, nor was diminished by nitrous air, and extinguished a 

 candle" (Experiments on Air, 1775, EL I 77)- 



The action of nitric acid on metals gives rise to 

 nitrous fumes, nitrous air, and diminished nitrous air, 

 In the action of nitric acid on metals, diminished nitrous 

 air is often formed, especially if weak acid be used ; being 

 soluble in cold water, but expelled by heat, the gas may be 

 set free by warming cold nitric acid in which iron, zinc, or 

 tin has been dissolved. 



"The solution of iron in spirit of nitre is known to 

 produce nitrous air ; but when all the nitrous air is pro- 

 duced in this manner, without foreign heat, if a candle be 

 applied to the solution, more air will be procured ; and 

 this will be possessed of the peculiar kind of inflammability 

 above mentioned. 



" I have also procured this kind of air in a direct process 

 by the solution of zinc and tin." 



" When ... I used only a very weak spirit of nitre 

 in the solution of zinc ... I got no other than this 

 kind of air in which a candle burned with an enlarged 

 flame ; and the air was of the very same kind from the 

 beginning to the end of the process " (" Of Nitrous 

 Air in which a Candle Burns," Experiments on Air, 

 1777, III., pp. 133, 134, 139). 



Berthollet (1785) prepares " diminished nitrous air " 

 or " laughing gas " by heating nitrate of ammonia. 



Berthollet discovered in 1785 that when nitrate of ammonia 

 is heated to about i5oC., it is decomposed into water and 

 " diminished nitrous air." This method of preparation was 

 used in the year 1799 by Sir Humphry Davy (1778-1829), 

 who found that the pure gas made by this method had the 

 following properties : 



a. A candle burnt in it with a brilliant flame, and 

 crackling noise. 



b. Phosphorus introduced into it in a state of inflamma- 

 tion, burnt with infinitely greater vividness than before. 



