MEMOIR OF PRIESTLEY. 145 



He finds it now in fixed air, wliicli is heavy and acid ; now in inflam- 

 mable air, whicli is light ; and again in phlogisticated air, which has 

 no property of the other two. Sometimes there are cases where an 

 accumulation of phlogiston diminishes the weight of the combination 

 and communicates an absolute levity to the mixture ; in other cases 

 it produces a directly contrary effect. Thus there is no uniformity, 

 nor is it possible to arrive at any general and precise conclusion. 



That conclusion it was left for modern chemistry to draw, and for 

 this purpose it has needed but one or two formulas. There is no such 

 thing as phlogiston; pure air (or oxygen) is a simple substance, as are 

 also phlogisticated air and injiammable air; combustion is only the com- 

 bination of pure air loitli combustible substances. These few words 

 have served to disembroil the chaos; every fact has fallen into its 

 proper place, and chemistry has emerged in the fair and consistent 

 form in which we possess it. 



But chemistry, like the gods of the pagans, could create nothing 

 out of nothing ; elementary material v/as still needed for its dispo- 

 sal, and this material, Priestley, beyond all others, has furnished. 

 Under this point of view, therefore, lie may justly be considered one 

 of the fathers of modern chemistry and be worthily associated with 

 the authors of that celebrated revolution in science. He was a father, 

 however, who never consented to recognize his offspring. 



His perseverance in combatting on behalf of his original ideas has 

 probably no parallel. Without being shaken in his convictions he 

 saw the most skilful defenders of those ideas pass into the opposite 

 camp ; and when Kirwan, the last nearly of all of them, abjured the 

 phlogistic doctrine, Priestley, unsupported and alone, still occupied 

 the field and addressed a new defiance to his opponents, the principal 

 Frencli chemists of his time. 



This challenge was at once taken up and replied to by Adet, who 

 was then ambassador of France to the United States, and thus proved 

 himself a worthy representative of French chemistry. The new argu- 

 ments of Priestley against that theory originated, in fact, from his own 

 want of familiarity with the operations of more recent chemistry, 

 liowever ingenious and dexterous he might be in those processes which 

 he had himself created. When he drew fixed air from substances 

 into which he did not suspect it of having entered, he would deny 

 that it invariably owes its origin to the carbon. And in forming water 

 from oxygen and hydrogen, though a 8m[i,ll quantity of nitric acid 

 was always present, he would take no account of the portion of azote 

 which produced it. 



His later writings failed, accordingly, to bring back to his opinion 

 any of those who had abandoned it. Like so many others who have 

 endeavored to arrest movements first communicated by themselves, he 

 experienced that ideas once dispersed abroad are as the seed whose 

 product depends upon the laws of nature^ and not the will of those 

 who have scattered them. To which we may add that, when they 

 have once taken root, no human power is any longer capable of eradi- 

 cating them. 



It remains now to trace, with painful interest, the career of Priest- 

 ley in that other branch of his labors to which reference has already 

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