CHEMICAL THEORY, [55 



most celebrated chemists, caloric is of two kinds ^ one of Dissertation oa 

 these is called caloric of temperature, which gives the sen- g{jp"forhJS 

 sation of warmth j the other is hidden in su-bstanccs", * so liVlit,-and com- 

 that its presence cannot be perceived but by certain changes ^"*'^i°"-. 

 which such substances may be made to undergo; thus we find 

 that ice at 32° contains much less heat than water at 32% t 

 though to the sense of touch they are the same.. The third 

 state in which I suppose heat is capable of existing, is as a 

 comwonent part of all inflammable substances, and is that 

 substance on which their combustibility depends; and this I 

 think it necessary to take for granted, to elucidate the phe- 

 nora.na of combustion, which I hope to do in this imperfect 

 memoir ; but as it is a thing necessary, for the truth of 

 cviey theory, that the data on which it is founded should 

 have truth for their basis, it may be prudent to state the 

 grounds on wh ch the present assumption is settled, especially 

 ss it is a common fault with speculators to build castles with- 

 out examining the foundation which is to support them, 

 and hence the superstructure being well increased, or per- 

 haps nearly finished, by a fault in the foundation, has sooqi 

 fallen prone; as has been observed in tiose build ngs which 

 were raised by Stah], Scheele, Di.s Cartes, ^<c. though, 

 at first sight, they appeared very fair, and exceedingly 

 strong. 



Since the reception of the Lavolserian theory of combus- 

 tion, some philosophers have supposed that the evolution of 

 caloric and light was from the oxigen gas alone, J others have 

 supposed that light was afforded by the S combustible sub- 

 stance, and heat by the oxigen gas, ]| which last opinion has 

 bad the greater number of folio ers. Some unable to ac- 

 count for the circumstance have supposed that light' and 

 heat are only different forms of the ** same substance. La- 

 voisier appears to have inclined to the opinion that t'.e light 

 was afforded by the ft oxigen gas, though he aUo suppo5ed 

 that the heat also might have the same origin. Before I 



* Dr. Black et alii, f Dr. Black, t Lavoisier, Brn!^nate]]i, &'c. 

 § Maquer, Richter, De la Metherie, Chcncvix, ! hompson, Gren, 

 Ct aiii. II Thompson, et csterl * * Murray's Chemistry, p. 178. 

 tfFourcroy. 



state 



