HISTORY of the SOCIETT. 25 



die intenfity of the heat and the extent of the bui-ning. In this 

 manner the parts of the niafs are kindled in fuccefllon, until the 

 whole is incandefcent ; it is at the fame time gradually confu- 

 med, the vital air uniting with the carbonic principle, and this 

 laft being deferted by the fixed light of the phlogifton. 



In the fulphurated mafs, though there be the fame appear- 

 ance of ignition propagated fucceilively from a central point 

 to the adjacent parts, yet it is not real ignition, but fimple in- 

 candefcence, produced from the extrication of latent heat, in the 

 manner already explained. It is diftinguiflied from ignition by 

 this circumftance : that, as foon as the incandefcence has fpread 

 over the whole mafs, there is an end of the generation of heat, 

 and the fulphurated metal cools from its incandefcent ftate, like 

 any other incombuftible body heated to the fame degree. In 

 the whole procefs there is no oxygenation ; no produdion of 

 fixed or carbonic air ; no apparent wafte ; nor any thing emit- 

 ted from the mafs, except the Ught of incandefcence. 



Thus, Dr Hutton concludes, that, in the procefs of the ful- 

 phurating of metals, we perceive the adlion of the fame laws as 

 in the converfion of water into ice, and muft explain both on 

 the great principle, by the difcovery of which his friend Dr 

 Black rendered fo important a fervice, not to chemiftry alone, 

 but to many other branches of natural philofophy. 



He is aware, however, that an explanation of it will alfo be 

 attempted by fome chemifts, on the principle of the change of 

 the capacity for heat ; an explanation which he confiders as ex- 

 tremely fallacious and unphilofophical. When he applies thefe 

 epithets to the dodrine of the capacities for heat, he does not 

 mean to objedl to the phrafe, capacity for heat, or to the ap- 

 plication of that phrafe to exprefs a mere matter of fadV, viz. 

 the difference of the fpecific heat of bodies, or the unequal 

 quantities of "heat contained in different fubftances, when their 

 Vol. IV. e maffes 



