£05 l>ESULPHUrvATlON OF METALS. 



ond as the sulphate of lead could uo longer mix with tlic 

 galena, there would be mo way oj desulphurating it. 

 *rhis the n>ost The roasting- of galena in the reverberatory furnace then is^ 

 sulnliu ration. i"educed to the conversion of the sulphur it contains into 

 sulphurous acid; and as this is in great measure effected by 

 the intervention of the sulphate of lead, wiiich is coatinually 

 forming, it admits a more complete clesulphuration than 

 other processes. 

 Decomposi- A similar decomposition of the sulphuret of lead by the 



Scotch furnace ^^^P^^**^ appears to uie also to take place in the treatment 

 similar. of lead ores in the Scotch furnace. In Scotland galena i* 



roasted and smelted in an uninterrilpted process by means 

 of coal and turf. 

 TTsed \»ithsuc- The same furnace is employed with success at Pezey for 

 cess at Pezey. fusi^o- roasted galena containing at least one third of its 

 weight of sulphate of lead. Its liual result gives no matts, 

 which proves, that it permits the decomposition of the sul-^ 

 phate, and the separation of the sulphur it contains. I con- 

 ceive, that the action of the part reduced to the state of sul- 

 phuret, by the contact of the charcoal, on the undecomposed 

 sulphate, is one of the principal causes of the desulphur- 

 ation effected. 



In some fiirna- S<mie furnaces have been mentioned, as that of Fahlun 



ce">sc:ircely 



any effect from and the Scotch, in which metallic sulphurets undergo a real 



roasting. roasting; but there are others, in vvhich this effect is scarcely- 



sensible. Some reflections on their differences in this res- 

 pect will probably not be out of place here ; and they will be 

 the more interesting, as they are intimately connected with 

 our subject, and account for phenomena, which are inexpli- 

 cable according to the idea generally entertained of roasting. 

 the higher the . It is a fact well known in smelting houses, that the highest 

 le Tsui \uir ftnnaces are least favourable to desulphuration, or in the 

 carried off, language of nvetallurgists produce the most noatts. If an 

 indisputable proof of this were required, I need only say, 

 that at Pezey I have seen roasted lead ores containing a 

 great deal of sulphate of lead, which smelted in the Scotch 

 furnace yielded not matts as the ultimate result, but pro- 

 duced a large quantity in the fourneau d tnauche [a kind of 

 |)igh furnace]. 

 Heat alone inr if heat alone could easily and completely decompose me- 

 effectual. . tallic 



