x NITRE, NITRIC ACID, AND NITROGEN 195 



87 volumes of oxygen and 7*4 volumes of nitrogen, i.e. one 

 volume of nitrous gas contained rather more than half its 

 volume of oxygen and rather less than half its volume of 

 nitrogen. It was left for Gay-Lussac in 1809 to show that 

 the ratios i : \ : J represent the composition of the gas by 

 volume more accurately than the figures given by Davy. In 

 doing this he had the advantage of being able to use the 

 very inflammable metal " potassium " which Davy had pre- 

 pared in 1807 by the action of an electric current on potash. 

 Gay-Lussac found that : 



" On burning the new combustible substance from potash 

 in 100 parts by volume of nitrous gas, there remained over 

 exactly 50 parts of nitrogen, the weight of which, deducted 

 from that of the nitrous gas (determined with great care by 

 M. Berard at Arcueil), yields as result that this gas is com- 

 posed of equal parts by volume of nitrogen and oxygen " 

 (A.C.R. IV. 14). 



Composition of nitrous fumes (nitrogen peroxide). 



The composition of the brown fumes of nitrogen peroxide 

 could not be determined by the methods employed in the 

 cases of nitrous oxide and nitric oxide, since it was 

 impossible to collect the gas over water or over mercury. 

 By admitting nitric oxide, oxygen, and water successively 

 into an exhausted globe and weighing at each stage, Davy 

 was able to calculate that the 100 parts of the gas contained 

 70 parts by weight of oxygen, and 30 parts by weight of 

 nitrogen ( Works, III. 15). But the experiment was 

 rendered complex by leakage of air into the globe 

 through the stopcocks, and by other sources of error for 

 which corrections had to be applied ; it will therefore be 

 convenient to describe in its place the more exact experiments 

 on the admixture of nitric oxide and oxygen which were 

 made by Gay-Lussac in 1816. Gay-Lussac measured the 

 contraction which took place when oxygen, confined over 

 mercury in a graduated tube, was admitted into a bulb con- 



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