240 The Rise of the Modern [lect. 



" candle burns in nitrous air, exposed to iron or liver of sulphur ; 

 " but as I had got nothing like this remarkable appearance from 

 " any kind of air besides this particular modification of nitrous 

 " air, and I knew no nitrous acid was used in the preparation of 

 " mercurius calcinatus, I was utterly at a loss how to account for 

 "it." 



He further mentions that " the flame of the candle besides 

 " being larger, burned with more splendour and heat than in that 

 " species of nitrous air ; and a piece of red-hot wood sparkled in 

 " it." 



He obtained the same gas from red precipitate and from 

 nimium ; he found that a mouse lived well in it, and on trying 

 it with his nitrous air he found that it was much better than, 

 four or five times as good as common air. It was therefore not 

 common air, it was the same thing as that which renders 

 common air fit for respiration, but as it were in a more con- 

 densed form. 



Priestley as I have said was devoted to the phlogiston 

 theory. He thought phlogiston ; he could not lay hold of any 

 subject save from the phlogiston point of view. Air supported 

 combustion because it took up the phlogiston given out by the 

 burning body. Common air was to a certain extent free from 

 phlogiston, it was dephlogisticated, and in proportion as it was 

 so dephlogisticated, it could support combustion. Common air 

 supported combustion to a certain extent only, a part only of it 

 could support combustion because it was only partially dephlo- 

 gisticated. The new air which he got from the metallic oxides 

 was wholly dephlogisticated. 



" I got air," says he, " which I was gradually satisfied had 

 "all the properties of common air, only in much greater 

 M perfection, so as to be entitled (according to my idea of purity 

 " or impurity with respect to air) to the name of dephlogisticated 

 " air, which for that reason I gave to it." 



He recognized the new thing which he had got not as a new 

 thing, a new gas or air, different from the rest of the atmosphere, 

 but as a part of the atmosphere brought into a new condition. 



He thus in 1774 prepared oxygen, he prepared the igneo- 

 aereal substance of Mayow, but he did not discover it, in the 



