BEGINNINGS OF MODERN CHEMISTRY 



At first this condensed matter was "acid to the 

 taste and contained two grains of nitre," but Caven- 

 dish, suspecting that this was due to impurities, tried 

 another experiment that proved conclusively that his 

 opinions were correct. "I therefore made another 

 experiment," he says, "with some more of the same 

 air from plants in which the proportion of inflammable 

 air was greater, so that the burnt air was almost com- 

 pletely phlogisticated, its standard being one-tenth. 

 The condensed liquor was then not at all acid, but 

 seemed pure water." 



From these experiments he concludes "that when a 

 mixture of inflammable and dephlogisticated air is ex- 

 ploded, in such proportions that the burnt air is not 

 much phlogisticated, the condensed liquor contains a 

 little acid which is always of the nitrous kind, whatever 

 substance the dephlogisticated air is procured from; 

 but if the proportion be such that the burnt air is al- 

 most entirely phlogisticated, the condensed liquor is 

 not at all acid, but seems pure water, without any ad- 

 dition whatever." 2 



These same experiments, which were undertaken to 

 discover the composition of water, led him to discover 

 also the composition of nitric acid. He had ob- 

 d that, in the combustion of hydrogen gas with 

 common air, the water was slightly tinged with acid, 

 but that this was not the case when pure oxygen gas 

 was used. Acting upon this observation, he devised 

 an experiment to determine the nature of this acid. 

 He constructed an apparatus whereby an electric spark 

 was passed through a vessel containing common air. 

 After this process had been carried on for several weeks 



