x NITRE, NITRIC ACID, AND NITROGEN 201 



The result of this experiment, in which nitrous air 

 combined with only half its volume of oxygen, did not 

 agree with those obtained by the analytical method, in 

 which the volumes were approximately equal. The 

 discrepancy led Lavoisier to suggest that the acid prepared 

 from nitre, which he had used for analysis, differed essen- 

 tially from the acid synthesised from nitrous air, and that 

 it was considerably richer in oxygen. 



Later investigators found that the proportions in which 

 nitric oxide and oxygen combined were not definite, but 

 varied widely with the conditions under which the experi- 

 ment was carried out ; the problem which Lavoisier had 

 attacked was indeed of altogether exceptional difficulty, and 

 forty years elapsed before the correct solution was given by 

 one of the brilliant group of Frenchmen who, in the early 

 years of the nineteenth century, resumed at Arcueil, near 

 Paris, the work which was so tragically interrupted by the 

 untimely death of Lavoisier. 



Combination of nitric oxide with oxygen to form nitric 

 and nitrous acids. When nitric oxide is added in suitable 

 proportions to common air or to oxygen confined over 

 water, the whole of the oxygen is removed and the water 

 becomes inpregnated with nitric or nitrous acid. The 

 method is fairly trustworthy as a means of absorbing or 

 estimating oxygen, but great variations were found in the 

 quantity of nitric oxide required to remove a given volume 

 of oxygen, and consequently also in the proportions of 

 nitrous air and oxygen in the resulting acid. Thus : 



Lavoisier found : oxygen : nitric oxide = TOO : 187 

 Dalton found : oxygen : nitric oxide 100 : 130 to 360 

 Davy found : oxygen : nitric oxide = 100 : 133 to 300 



Such variations were not difficult to understand in view 

 of Cavendish's observation that when water impregnated 

 with the mixed gases was distilled in a glass retort : 



