CH. xxvii. PRIESTLE Y*S DISCO VERIES. 233 



Here, you see, we have come back again to Mayow's 

 fire-air, so long forgotten, which supports life and flame. 

 Priestley had learnt more about it than Mayow had, for he 

 had collected it separately, had shown that it is the gas 

 which supports combustion, and had breathed it without 

 other air being mixed with it ; moreover, he had shown that 

 it could be driven out of metallic compounds, for mercury 

 is a metal. Yet it is disappointing to learn that, in spite 

 of having gone thus far, Priestley was so imbued with Stahl's 

 theory of 'phlogiston,' that he did not really understand 

 the great discovery he had made, but called his gas 

 1 dephlogisticated air,' or air which had lost that imaginary 

 * phlogiston ' which was always confusing men's minds. 



There is no doubt that he discovered the gas and showed 

 that it was the chief actor in combustion and respiration, 

 and for this discovery and that of other gases, he was 

 elected a member both of the Royal Society and of the 

 Academic des Sciences, and his fame was great all over 

 Europe ; yet still he had not hit upon the entire truth 

 he had given the facts, and it remained for Lavoisier to 

 read the riddle. 



Besides his chemical writings, Priestley published many 

 books on theology, and though he was a singularly gentle 

 quiet man, yet his religious and political essays were often 

 very severe, and they led to his being driven out of Bir- 

 mingham, and his house burnt by the mob, when they 

 attacked the leading Dissenters during the panic caused by 

 the French Revolution. After living for some time near 

 London he emigrated to America, where he died in 1804. 

 He continued his chemical experiments up to the time of 

 his death, and made many important discoveries, but the 

 chief discovery which will always be connected with his 

 name was that of oxygen, in 1774. 



