Tesson xxvin.] FIRE. 18* 



different bodies : as when bodies manifest the 

 same temperature by the test of the thermometer* 

 the relative quantity of caloric which they contain 

 is, we discover, very different. Much ingenuity 

 and acute investigation have been employed toj 

 ascertain the absolute quantity of caloric which* 

 they contain. These endeavours have not, per- 

 haps, been as yet completely successful. 



Dr. Black discovered, that whenever a solid le- 

 romes a fluid, a great portion of heat enters into it, 

 which does not affect the thermometer j and that, 

 on its again becoming solid, this portion of heat 

 quits it, without a diminution of its temperature 

 taking place. Snow at 32, being mixed with an 

 equal quantity of water at 172, the snow melts, 

 and the mixture is only 32"> j so that the water has 

 parted with 14O 1 , which has disappeared, and has 

 combined with the snow, shewing that snow or 

 ice, during its change into water, absorbs, and, in- 

 deed, combines with 140, of caloric. It also ap- 

 pears that water, though cooled down to 32", does 

 not freeze until it has given out 140 of caloric : 

 on the absorption, or the parting with this dose of 

 caloric, depends therefore the fluidity or solidity of 

 water. Not only the fluidity of such bodies as 

 liquify, but the softness of such bodies as acquire 

 this state by heat, depends also on the quantity of 

 heat which thus combines with them> The mal 

 leability and ductility of metals likewise depends 

 on the same cause. The quantity of heat thus im- 

 bibed, Dr. Black calls latent heat ; since it does 

 not manifest itself by its effects on the thermo- 

 meter. 



