PHLOGISTIC THEORY. 137 



theory, combines with and oxidates it, Stahl sup- 

 posed that the phlogiston separated from the metal 

 and combined with the acid. That the explanations 

 of the phlogistic theory are so generally capable of 

 being translated into the oxygen theory, merely by 

 inverting the supposed transfer of the combustible 

 element, shows us how important a step towards the 

 modern doctrines the phlogistic theory really was. 



The question, whether these processes w r ere in 

 fact addition or subtraction, was decided by the 

 balance, and belongs to a succeeding period of the 

 science. But we may observe, that both Beccher 

 and Stahl were aware of the increase of weight 

 which metals undergo in calcination ; although the 

 time had not yet arrived in which this fact was to 

 be made one of the bases of the theory. 



It has been said 3 , that in the adoption of the 

 phlogistic theory, that is, in supposing the above- 

 mentioned processes to be addition rather than 

 subtraction, " of two possible roads the wrong was 

 chosen, as if to prove the perversity of the human 

 mind." But we must not forget how natural it was 

 to suppose that some part of a body was destroyed 

 or removed by combustion; and we may observe, 

 that the merit of Beccher and Stahl did not consist 

 in the selection of one road of two, but in advanc- 

 ing so far as to reach this point of separation. 

 That, having done this, they went a little further on 

 the wrong line, was an errour which detracted little 

 3 Herschel's Inlrod. to Nat. Phil. p. 300. 



