ao4 On the different Theories of Vhilofofhers 



procefs of combiiftion, and formed a rcfiduum that is incom- 

 buftible, we heat this latter fubllance with charcoal (an in- 

 flammable body), the metal will be again revived — phlogillon 

 is imparted to it from the charcoal, and we again procure a 

 conibuftible fubftance. Thus, the light and heat which are 

 evolved during combulHoii are fuppofed to proceed from the 

 burning body, and to be occafioncd by the feparation of 

 phlogillon from the bafe to which it is united. 



Such is the outline of that theory of conibuftion the foun- 

 dation of which was firli; laid by Becher, %nd afterwards re- 

 duced iyto a regular fyilem by the immortal Stahl. The 

 phlogiftic do(Slrine of this chemift was vmiverfally adopted 

 until the middle of the prefcnt century, when the difcoveries 

 of Mayow and flooke, of Priedlev and Lavoilier, led the 

 way to a new theory of combuftion, which foon difplaced 

 the former, a)id eftablilhed itfelf on its ruins. Stahl, from 

 being wholly occupied in demonftrating the exigence of phlo- 

 gifl:on, fterns to have paid no attention to the influence of 

 air on combuftion. The experiments of Bovle and of Hales 

 had already pointed out the influence of this element on many 

 of the phaenomena of combuilion, and the incrcafe of weight 

 that bodies acquire during fuch a procefs, is a fa£l totally 

 irreconcileable with tlie theory of phlogifton. ' 



Many attempts, however, were made to overcome the 

 wei<zht of this objection by the difciples of Stam ; and they 

 even had recourfe to the fuppofition that phlogiflon was the 

 principle of levity, and that, when abftra(!-"ted from any body, 

 that body, by lofing fo much'ablolute levity, became heavier. 

 So ftronnly were they fettered bv the tenets of their mailer, 

 that, without fubmitting to the labour of invefligation, they 

 implicitly adopted any illuftration that was conformable to 

 his ideas; afibrding a flrong proof of^ the defire that pervades 

 the hunijin mind to reduce every thing to firft principles, and 

 to adopt hafty generalizations, without haviug recourfe either 

 to an extenlive coUeftion of fads or the more certain evi- 

 dence of accurate experiment. 



Whilft other chemilis were intent on r«conciling the va- 

 rious difcoveries that had been recently made with the hy- 

 pothefis of Stahl, Lavoifier (of a bold and creative genius) 

 was led to call into quellion the very exiitence of phlogiflion 

 itfelf. This arofe From his having diicovcred that during the 

 procefs of combuilion a portion of air conftautly enters into 

 union with the body which is made to undergo this opera- 

 tion, and that the weight of the air which diiappcars in the 

 procefs is exactly equal to the increafe of weight gained by 



the 

 8 



