COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN 291 



combination with the oxygen ; hence in this reaction equal volumes of 

 nitrogen and hydrogen replace each other. Nitrous oxide is also very 

 easily decomposed by red-hot metals ; and sulphur, phosphorus, and 

 charcoal burn in it, although not so brilliantly as in oxygen. An equal 

 quantity of a substance in burning in nitrous oxide evolves more heat 

 than in burning in oxygen ; which most clearly shows that in the 

 formation of nitrous oxide by the combination of nitrogen with oxygen 

 there was not an evolution but an absorption of heat, there being no 

 other source for the excess of heat in the combustion of substances in 

 nitrous oxide. If a given volume of nitrous oxide be decomposed by 

 a metal for instance, sodium then there remains, after cooling and 

 total decomposition, an exactly equal volume of nitrogen to that of 

 the nitrous oxide taken ; consequently, the oxygen is, so to say, distri- 

 buted between the atoms of nitrogen without producing an increase 

 in the volume of the nitrogen. 



u 2 



