Chemical Effects of Caloric, 8$c. 69 



pending upon the quantity of sensible or obvious 

 heat ; but though it may render the subject ra- 

 ther complex, we shall find there is something 

 else to be attended to. From facts and experi- 

 ments it is proved that fluidity does uot depend 

 upon the sensible heat, or that which we perceive 

 in bodies by our senses, and by the thermometer, 

 but upon a certain quantity of what Dr. Black 

 called latent heat, imperceptible to us, but ready 

 to emerge on proper occasions and assume a 

 sensible form. I mean by obvious or sensible 

 heat, that which is so far in a fluctuating state, 

 that if you apply any body which contains an 

 excess of it to a cooler one, it immediately 

 leaves the hotter, and flies to the cooler body, so 

 as to restore an equilibrium. This will be the 

 case of all bodies which are conductors of caloric . 

 or heat, and in proportion to their conducting 

 power, while they do not change their state ; 

 but when they are about to change, their tem- 

 perature or sensible heat is not increased, for 

 the caloric is absorbed, and instead of being 

 sensible, serves to render them fluid. Thus ice 

 conducts caloric at any degree below the freezing 

 point, and a sensible increase of the temperature 

 may be observed in it till it reaches that point, 

 viz. 32; but when it has attained that degree it 

 will remain at or near it till the whole is melted. 

 The reason is clear, that when arrived at this 

 point, the body is in a state for the absorption 

 of caloric, which process goes on without any 

 increase of temperature till the whole is rendered 



