20 JOSEPH PRIESTLEY i 



diminished to four-fifths, it almost completely 

 vanished, and, therefore, showed itself to be " be- 

 tween five and six times as good as the best 

 common air I have ever met with." * As this new 

 air thus appeared to be completely free from 

 phlogiston, Priestley called it " dephlogisticated 

 air." 



What was the nature of this air? Priestley 

 found that the same kind of air was to be obtained 

 by moistening with the spirit of nitre (which he 

 terms nitrous acid) any kind of earth that is free 

 from phlogiston, and applying heat; and con- 

 sequently he says: " There remained no doubt 

 on my mind but that the atmospherical air, or 

 the thing that we breathe, consists of the nitrous 

 acid and earth, with so much phlogiston as is 

 necessary to its elasticity, and likewise so much 

 more as is required to bring it from its state of 

 perfect purity to the mean condition in which we 

 find it." t 



Priestley's view, in fact, is that atmospheric air 

 is a kind of saltpetre, in which the potash is re- 

 placed by some unknown earth. And in speculat- 

 ing on the manner in which saltpetre is formed, he 

 enunciates the hypothesis, " that nitre is formed 

 l)y a real decomposition of the air itself, the hases 

 that are presented to it having, in such circum- 



♦ Experiments and Observations on Different Kinds of 

 Air, vol. ii. p. 48. f Ihid. p. 55. 



