CHEMICAL THEORY. j^"^ 



and, at length, I^avoisier. In the remotest ages fire was sup- Ks^ertation on 

 posed to be a substance which, by being applied to certain j.«^H^'^orhta» 

 other substances, devoured them, and what was left was sup- li.i^bt, and com- 

 posed to be unfit for the * food of fire : to this succeeded the *'"-^^'*^ 

 opinion that a t solvent acting rapidly on the combustible, was 

 the cause of the evolution of heat and light; to this the suppo- 

 sition tbat violent friction and J agitation between the combus- 

 tible and a matter existing in the air was the cause of the 

 phenomcnori. This was followed by the hypothesis that in- 

 flammables had the peculiarity of § running into violent whirl- 

 ings, by which combustion was produced ; the next opinion 

 was thai light existed in a |I dense state in all inflammables, 

 and by certain actions was set free ; afterwards a peculiar very 

 subtile,** most elastic fluid, was supposed to be condensible, 

 in certain bodies, from which it escaped, and produced certain 

 appearances, among which was combustion. This hypothesis was 

 superseded by the opinion that heat and light were evolved 

 by the ff air, which combined with the inflammable body, at 

 the same time giving out a certain principle which rendered 

 the air afterwards incapable of supporting combustion ; after 

 this combustion was supposed to depend on a substance which 

 y/aa the same in all combustibles J |. This theory was the last 

 to overturn, and was succeeded by that which stated that 

 during combustion oxigen gas was §§ always absorbed. This 

 theory is certainly the best, and appears to have a firm foun- 

 dation, but it evidently fails in explaining the most striking 

 phenome;ia of combustion, viz. the [ij| origin of the heat and 

 light, which is the very essence of combustion. It is the pro- 

 vii-ce, therefore, of this paper to explain the probable sources 

 of these substances ; though, from the extreme intricacy of the 

 subject, it is with great diffidence that I do it. 



It may be proper, before inlmediate procedure to the business, 

 to notice those substances which are necessary to constitute 

 combustion. Authors inform us, that oxigen gas and an 



* Albortus Magnus et alii. | Ilooke. | Mayow. 



^ Stiihl Scheele et alii. || Macquer. ** Newton, 



ft Crawford. ttl'^irwan. §§ Lavoisier. 



j-i 'I Murrrty et alii. 



Y 2 an 



