Lesson xxviii.] FIRE. 185 



out undergoing a change of temperature ; and 

 that on their reduction to a liquid state, a portion 

 of heat is givtn out, and likewise without mani- 

 festing any change of temperature. 



Thus it appears, that by a certain dose of caloric 

 solid bodies become liquid, and that by a farther 

 dose they acquire a gaseous form. Hence the ge- 

 neral law discovered by Dr. Black ; Whenever a 

 lody changes its state, it either combines with 

 caloric, rr separates from caloric. 



Dr. Irvine admitted the importance of the facts 

 discovered by Dr. Black ; but supposed, that the 

 quantity of heat absorbed by different substances 

 depended on the capacities which those sub- 

 stances possessed for heat: and which he ascer- 

 tained was different, in different substances ; and, 

 in the same substances, under different forms. He 

 also believed that the heat thus absorbed does not 

 exist in any peculiar state : he therefore objected 

 to the term latent heat, when intended to imply 

 such a circumstance. 



It has been likewise ascertained, that on salts, 

 which contain much water in their composition, as 

 muriate of lime, &c. being dissolved in waier, the 

 temperature sinks considerably ; but if previously 

 deprived of their water, the temperature rises. This 

 is to be explained by this law that when the 

 compound, formed by the union of two bodies, is 

 more dense or fluid than the mean density or 

 fluidity of the two bodies before mixture, then the 

 temperature is diminished : but when the fluidity 



or 



