134 CHEMICAL DISCOVERY AND INVENTION 



to displace, with adjustments, exactly the same volume of air. 

 The weight of the gas contained in the globe could thus be found, 

 and, as the capacity of the globe had been previously deter- 

 mined, the volume of the gas was also known. 1 



Having experimented on hydrogen and oxygen the case of 

 nitrogen came to be considered, and an anomaly was soon dis- 

 covered. 2 It was found that when the nitrogen had been pre- 

 pared from atmospheric air by removing the oxygen by any 

 suitable agent, the gas proved to be heavier than the nitrogen 

 made by chemical decomposition of ammonia or one of the 

 oxides of nitrogen. Hence it might be supposed that the atmo- 

 spheric nitrogen was too heavy on account of imperfect removal 

 of oxygen, or the chemical nitrogen was too light in consequence 

 of its contamination with gases lighter than pure nitrogen. It 

 was proved by direct and laborious experiments that neither of 

 these hypotheses could be adopted. 



The following figures represent the weights of nitrogen, made 

 from different materials, with which the experimental globe was 

 filled. (Proc. Royal Soc., vol. 57, p. 267.) 



Nitrogen obtained from nitric oxide, NO . . 2-3001 grms. 



nitrous oxide, N 2 . 2-2990 



ammonium nitrite, NH 4 N0 2 2-2987 



Nitrogen was also made from air by first combining it with 

 magnesium to form magnesium nitride, acting on this com- 

 pound by water so as to produce ammonia and decomposing the 

 ammonia by a hypochlorite. The nitrogen was finally purified 

 by passing it over red-hot copper, and copper oxide. 



The weight was then 2-29918 grams, and was therefore practi- 

 cally the same as above. Nitrogen obtained from atmospheric 

 air by removing the oxygen by means of 



Red-hot copper . . . 2-3103 grams. 

 Red-hot iron .... 2-3100 

 Ferrous hydrate . . . 2-3102 



These figures correspond to the following weights per litre of 

 the gas : 



Chemical nitrogen . . . 1-2505 grams. 

 Atmospheric nitrogen . . 1-2572 



1 Rayleigh, Proc. Royal Soc., 53 (1893), p. 134. 



2 Proc. Royal Soc., 55 (1894), p. 340. 



