20Q UESULP^!J9.ATfjON QF METALS. 



fprg- fre jected to a forge irie «ome powdered galeim in a cruoibJe 

 vTihlsLrhiur ^^"^'^^ ^"'^ covered w,>h charcoal powder. The result was a 

 pxpeile4. itass. ihat had fjeen well fused, and resembled what metal-r 



lurgists call lead matt Tliere was in it no lead united to- 

 gether, but some parts of the button were merely a little 

 ductile. By analysis I found, that about three fiftl)s of the 

 ;^03s -27 from gulphur still remained. Part of the loss it had experienced 

 fi2aS)i7" ^''' ^y ^'^^ action of the lire, which was 27 per cent, I ascribed to 

 the vplatizatipn of a portion of the suiphuret; for that owing 

 ^p the separation of the sulphur could not have exceeded G 

 per cent at most. 



Galena then is but yery imperfectly decomposed by heat. 

 I shall npt speak particularly of tlie sulphurets of zinc, 

 antimony, &c., because I am npt acquainted with any expe* 

 riments sufficient to determine with certainty the eiTects, 

 that heat produce^ on them : but I am led to believe froa^ 

 analogy, that it does not decompose them completely. 

 Heat alone All the facts I have adduced appear to me to evince, that 



ihen expels ^^e action of .caloric a:lone on metallic sulphurets, and par- 

 but little oi the _ ^ . 



sulphur. ticulurly pn those of iron, copper, and lead, is limited to 



%he taking from them a small portipn of the sulphur con? 



t.ained, an4 aftejrwg^rd fusing and even volatilizing them, 



Sect. 11. 



Of the simultaneous action of heat and air on metallic sul' 

 phineis. ' 



Roasting by That metallurgical process, thp object of which is the de- 



the joint action 

 of heat and air. 



the iomt action gulphuration of metals, is known by the name of roasting. 



Most authors, who have treated of it, seem to Consider ca- 

 loric as the sole agent in" the decomposition ; and even those 

 who have remavked the influence of the air, since the esta*- 

 blishment of- the new chemical theory, have not considerecJ 



^ . , it as essential. The experiments 1 have collected having^ 



Oxigen has a • : , ^ * ^ . ^^ 



great share iu ^hpwn tiie insufficiency of heat alone to decompose a metal- 

 ^^' lie suiphuret, the oxigen of the air must be considered as 



having a g'reater ^hare in the desulphuration of metals by- 

 toasting. The affinities both of sulphur and metalHc sub- 

 stances for this principle render it very probable ; and it i^ 

 likewise proved by the chemical examination of the product^ 



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