Biographical Memoir of Henry Cavendish. 215 



never existed : it was that of the composition of nitrous acid, a 

 substance of great utility in the arts, and very extensively dif- 

 fused in nature, respecting which, before Mr Cavendish''s time, 

 chemists had only vague and hypothetical ideas *. Ever since 

 his first experiments on the combustion of inflammable air, he 

 had perceived that nitrous acid was formed, and that it was 

 the more abundant in proportion to the quantity of what was 

 then called dephlogisticated air, and afterwards named azote. 



Upon examining the product of the detonation of nitre by 

 charcoal, he found it composed of this same phlogisticated air, 

 and fixed air. Now it was the charcoal that yielded the latter ; 

 the former, therefore, could be furnished only by the acid of the 

 nitre. Mr Cavendish quickly proved, by direct experiments, 

 the accuracy of his conjecture. By burning a mixture of re- 

 spirable air and phlogisticated air, by means of the electric spark, 

 he converted it into nitrous air, which was itself changed into 

 acid by a new addition of respirable air. Thus the elements of 

 nitrous acid were found to be the same as those of the atmos- 

 phere, but in different proportions ; and from henceforth clear 

 ideas were obtained of the universal, and hitherto incomprehen- 

 sible, generation of that acid. 



The history of this epoch, the most brilliant that chemistry 

 ever had, cannot be read without exciting a sort of enthusiasm> 

 Discoveries seemed to press upon each other. Mr Cavendish, 

 having communicated that which he had just made respecting 

 nitric acid to our fellow-member M. Berthollet, received from 

 him in return, that of the decomposition of ammonia into in- 

 flammable air and phlogisticated air. What men and what 

 times must those have been ! 



Mr Cavendish at length undertook the examination of the 

 atmosphere itself. It produced such varied effects upon living 

 beings, that it was natural to suppose that it must be highly 

 variable in the proportion of its elements. Priestley, who dis- 

 covered pure or respirable air, had also ascertained the means 

 of estimating the respirabihty of any given air ; all that was 

 for this purpose necessary, was to measure the proportion of it 

 which was absorbed, when it was mixed with nitrous air ; but 

 his instruments were still imperfect, notwithstanding the cor- 



• Phil. Trails. 1786 ; Jour, de Phys. t. xxvii. p. 107. 



