JOSEPH PRIESTLEY. 119 



of the properties of this new kind of air for seven 

 months, or until March 1775, when he found that the 

 new air behaved with " nitrous gas " in the same way 

 as the dephlogisticated part of common air does ; * but 

 that, instead of being diminished to four-fifths, it almost 

 completely vanished, and, therefore, showed itself to be 

 "between five and six times as good as the best com- 

 mon air I have ever met with." f 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 moisten- 

 ing with the spirit of nitre (which he terms nitrous 

 acid) any kind of earth that is free from phlogiston, 

 and applying heat ; and consequently he says : " There 

 remained no doubt on my mind but that the atmos- 

 pherical 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.";f 



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

 is a kind of saltpetre, in which the potash is replaced 

 by some unknown earth. And in speculating on the 

 manner in which saltpetre is formed, he enunciates the 

 hypothesis, " that nitre is formed by a real decomposition 

 of the air itself, the "bases that are presented to it hav- 



* " Experiments and Observations on Different Kinds of Air," vol. ii. 

 p. 40. f Ibid. p. 48. \ Ibid. p. 65. 



