1(34 CHEMICAL THEORY. 



Dissertation o» * inflammable substance are necessarily present in every 

 «=ffe.cts*orheat ^^^® °* combustion, but in the present speculation I am under 

 light, and com- the necessity of supposing both oxigen gas and combustibles 

 7US jon. compound substances, so that we have four substances present 



in every case of combustion^ — oxigen, light, the base of an in- 

 \ flanamable substance, and heat. 



In speaking of caloric and light, we do not think it necessary 

 to enter into the subject minutely, but only to mention those 

 circumstances respecting them which are allied to our theory. 

 With regard to the mode of existence of heat, there is 

 still some dispute among philosophers, some supposing that it 

 is a property produced by the motion of a very subtile cetherf, 

 which pervades all space; others, that- it is a real substance, 

 sometimes giving a sensation to the sense and touch, but 

 often so hidden J in bodies, that its presence cannot be per- 

 ceived. Perhaps the latter opinion is the best, for by it we are 

 the better enabled to treat of the subject. As I mentioned 

 before, this substance is capable of entering into chemical union 

 with certain other substances; in which case it can only be 

 discovered by certain properties which those substances pos- 

 sess, and this property is that of inflammability ; here there- 

 fore I differ in opinion from most philosophers, who suppose 

 that heat exists latent in greatest quantity in certain aerial 

 susbstances, as oxigen, carbonic acid, &c. § which I profess 

 to have none, unless that which regards the temperature of 

 such bodies, for I am not inclined to deny the circumstance 

 that different substances require different portions of heat to 

 make them of an equal temperature ; on the contrary, I suppose 

 tliat the experiments of Crawford, Irvine, &c. with respect to 

 -the capacities of bodies for heat, are as accurate as the sub- 

 ject will allow ; but the heat, which I call latent, has no effect 

 in increasing temperature ; a quantity of sulphur at plus one 

 hundred degrees, contains as much, and no more, of that la- 

 tent heat, than the same portion would at the most intense 

 cold ever observed. 



Perhaps it will be better to state in what the peculiarity 

 of my opinion coosists. According to the writings of the 



^ * Thompson et multi alii. f Newton. Leslie. ^ Black. 



§ Crawford. 



most 



