3© HlSrORr of the SOCIETr. 



diminifh it. The volume of the fulphur is obvloufly much 

 diminifhed on its combination with the metal ; and therefore a 

 quantity of its conjiitutional beat muft be expelled, correfpond- 

 ing to the condenfation or diminution of bulk which it has un- 

 dergone. This quantity may be very great ; but it is what at 

 prefent our fcience has not the proper means of eflimating. 

 ^ Such are the fources of heat contained in the fulphur. The 

 mietal alfo, by lofing its ducftility, may emit a certain quai^tity 

 of latent heat, and may thus contribute to increafe the fenfible 

 heat of the compound mafs. The quantity of this effecfl, like 

 the former, it is difficult to eflimate. 



These, then, are the different fpecies of latent heat, which 

 may be fuppofed to emerge, and become fenfible, on the com- 

 bination of the fulphur and the metal in the preceding experi- 

 ment, and on the inflantaneous concretion of the compound 

 mafs. The confequence of this muft be, that the mafs already 

 heated, from without, nearly to a red heat, having this addi- 

 tional heat commiunicated, muft become incandefcent, and emit 

 light. This mufl happen, even if the latent heat emerging 

 Ihould be but in a very fmall quantity; and thus the leading 

 fa(5l of the incandefcence feems to be fufficiently accounted for. 



It may alfo be ufeful to remark, that there are other cafes in 

 which incandefcence feems to be produced, on the principle 

 here affigned, though not perhaps in a degree equally remark- 

 able. 



In the afTaying of filver on the teft, when the lead is fuffi- 

 ciently feparated, fo as to leave the filver ftill fluid, but in a 

 degree of heat inferior to what is required to melt it, or to 

 preferve its fluidity, the button of filver inftantly concretes, 

 and appears at the fame time much more luminous. Here 

 there is evidently no caufe that operates, but the latent heat of 

 fluidity, emitted, as on all occafions, when concretion takes 



place J 



