A HISTORY OF SCIENCE 



a small amount of liquid was formed. This liquid 

 combined with a solution of potash to form common 

 nitre, which "detonated with charcoal, sparkled when 

 paper impregnated with it was burned, and gave out 

 nitrous fumes when sulphuric acid was poured on it." 

 In other words, the liquid was shown to be nitric 

 acid. Now, since nothing but pure air had been used in 

 the initial experiment, and since air is composed of ni- 

 trogen and oxygen, there seemed no room to doubt that 

 nitric acid is a combination of nitrogen and oxygen. 



This discovery of the nature of nitric acid seems to 

 have been about the last work of importance that Cav- 

 endish did in the field of chemistry, although almost 

 to the hour of his death he was constantly occupied 

 with scientific observations. Even in the last moments 

 of his life this habit asserted itself, according to Lord 

 Brougham. " He died on March 10, 1810, after a short 

 illness, probably the first, as well as the last, which he 

 ever suffered. His habit of curious observation con- 

 tinued to the end. He was desirous of marking the 

 progress of the disease and the gradual extinction of the 

 vital powers. With these ends in view, that he might 

 not be disturbed, he desired to be left alone. His ser- 

 vant, returning sooner than he had wished, was ordered 

 again to leave the chamber of death, and when he came 

 back a second time he found his master had expired." 3 



JOSEPH PRIESTLEY 



While the opulent but diffident Cavendish was mak- 

 ing his important discoveries, another Englishman, a 

 poor country preacher named Joseph Priestley (1733- 

 1804) was not only rivalling him, but, if anything, 



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