HISTORr of the SO'CIETT. 29 



This rule feenis to be no other tliah that which reguktes the 

 extrication of latent heat, when bodies pafs from a fluid to a 

 folid flate, though this cafe is fomewhat more complicated than 

 iifual, and attended with circumftances that are yet but imper- 

 fedly underflood. It muft therefore be confidered, whether 

 the fources of latent heat in the bodies, here combined,. be fuch 

 as we can reafonably fuppofe adequate to th^ effect produced. 



First, then, we have the latent heat of the fulphur, when it 

 is fimply in its melted flate j it has then an aqueous or perfe(5t 

 fluidity, to which the quantity of its latent heat necelTarily cor- 

 refponds. But this is not precifely the ftate in which the ful- 

 phur combines with the metal ; for before that happens, and 

 while the fenfible heat increafes, the ililphur becomes vifcid, 

 and lofes its perfedl fluidity. We have nothing with which we 

 can compare this phenomenon, or by which we can ellimate 

 the latent heat now contained in the fulphur. There is how- 

 ever reafon to think, that this heat is of the fpecies which Dr 

 HuTTON, in his DifTertations on fubje<3:8 in Natural Philofophy, 

 diftinguifhes by the name of the latent heat ofdu6lility. The reafon 

 for this fuppofition is, that when the fulphur, in its vifcid flate, 

 is plunged into cold water, it does not concrete into its ufual, 

 hard, friable, and cryflallized flrudlure, but is changed into a 

 tranfparent dudlile mafs. This flate it feems to owe to the la- 

 tent heat contained in it; for after fome hours expofure to cold, 

 it gradually lofes its ducflility, and undergoes another change 

 of flrudlure, fo as to refume its ordinary appearance, as if it 

 had been concreted and cryflallized from the flate of fimple 

 fluidity. 



But the fulphur alfb emits another fpecies of heat, on its com- 

 bination with the metallic fubflance. This is what may be 

 called the conflitutional heat of a body, or that by which its 

 volun^e is preferved in oppofition to any force endeavouring to 



diminifh 



