207 



tent, solids are converted into fluids, and fluids into 

 vapours and airs. The rarity and specific caloric of 

 bodies, however, though intimately connected, are 

 by no means proportional to each other. Solid bo. 

 dies contain less caloric than fluids, and fluids less 

 than airs ; and, when a change of form in these bo- 

 dies takes place, caloric either enters into, or is gi- 

 ven out by them. Dr Black, whose admirable dis- 

 coveries relating to heat, form so brilliant a period 

 in the history of modern chemistry, found, that ar 

 quantity of heat, equal to 140 of Fahrenheit, was 

 required to convert ice into water, although the wa- 

 ter still continued at the temperature of 32 : and to 

 raise water into vapour required 800 more, although 

 the temperature of the steam did not exceed that of 

 boiling water. As the caloric employed in producing 

 these changes of form, did not sensibly raise the 

 temperature of bodies, he called it latent heat : and 

 he shewed that this latent heat was again given out 

 when the vapour was reduced to water, or the wa- 

 ter passed into the state of ice. The permanently 

 elastic fluids are subject to the same laws ; for when 

 on being disengaged from a combination, they as- 

 sume a gaseous form, a large quantity of caloric, in 

 a latent state, unites with them, which is again libe- 

 rated, whenever, by compression, or by chemical 

 combination, they are reduced to a denser state. 



165. Many experiments have been made to disco- 

 ver the comparative quantities of heat, or the speci- 

 fic caloric which, at a given temperature, equal 

 weights of various solid, liquid, and aeriform bodies 

 contain. Taking the specific caloric of water as 

 1.0000, Dr Crawford found that of arterial blood 



