HISTO.RT of the SOClE^Tr, 31 



place; and had the filver been here, in the loweft degree of hv 

 candefcence, or the highefl degree of obfcure heat, the pheno- 

 menon would have been as remarkable as m the fulphurating 

 of metals. 



On the fame principle it feems to be, that, in a very common, 

 but very inftrudlive experiment, a bar of cold iron is made in- 

 candefcent.^ by hammering it with a certain degree of rapidity 

 and force, fo that the condenfation may be fufEciently quick to 

 €xpel the heat all at the fame time, or nearly fo. In this cafe, 

 it is the latent heat of dudlility that is made to appear, as in the 

 congelation of water it is the latent heat of fluidity. 



Iron alfo furnilhes another example of the fame kind, where 

 the incandefcence is very confpicuous, but where the procefs is 

 not fo fimple as in the former inftances, becaufe a part of the 

 light is probably produced from another caufe. This example 

 is found in the converiion of pig iron into malleable iron by 

 Mr Corte's procefs, viz. by keeping the iron melted in a re- 

 verbatory furnace, and expofed, by being agitated, to the influ- 

 ence of the atmo{phere. When the call iron comes in this man- 

 ner to its malleable ftate, it quickly difplays the brighteft incan- 

 defcence poffible, coagulating, at the fame time, from its melted 

 ftate. Now, there can be no doubt that this ex:treme incandef- 

 cence arifes from the commutation of latent into fenfible heat, 

 and the commutation of that heat again into light, in which 

 ftate it is emitted by the incandefcent body. In this cafe, how- 

 ever, it is probable, that there is alfo^ light emitted immediately 

 on the principle of burning, and that the iron is in part fcori- 

 fied, by being oxygenated and lofing its phlogifton. But this 

 alfo is in a great meafure owing to the extreme heat produced 

 by the congelation of the iron; for the heat of melted iron is 

 not alone fufficient for that effedl. 



The theory above laid down will enable us to explain all 

 the different fteps in the complicated procefs of the fulphurating 



of 



