O0O DESUI.PHURATIQN OF METALS. 



posed to allow a much more complete separation of the sul- 

 phur than that conducted in the open air. If it do not, tliis 

 no doiibt is owing to the difficulty of preventing the agglu- 

 tination of the sulphuret produced by the elevation of tem- 

 perature arising from the rapid and unavoidable combustion 

 of a large quantity of sulphur, 

 ywrnace at j^ reujains for me to speak of a furnace, in which both 



the smeltmg and roastmg or the pyntous copper, to a cer- 

 tain point, are effected at the same time. It is used at Fah- 

 lun in Sweden. This has an interior crucible, which receives 

 the product of a smelting of 24 or 48 hours, and in which a 

 separation, or rather combustion, of the sulphur is effect- 

 Blast of airdi- €'d. A stream of air from the bellows is made to blow on 



Tected on the ^]^g melted mass with such force, as to drive off the scoriae, 

 metal. 



and burn a part of the sulphur that is found on the surface. 



The iron is thus oxided, and quartz is added to vitrify it in 



proportion as the roasting goes on. This process is perhaps 



the only one, in which sulphur and iron are separated «in so 



large a quantity at the same time. 



"Progress of de- The desulphuration of pyritous copper by roasting ap- 



^ulphuration. pears to me to be effected, 1st, by the sublimation of a small 



portion of sulyjhur, which may either be collected, or burned 



in the air: 2dly, by the disengagement of sulphurous acid, 



which is the more abundant in proportion as the process is 



well managed: 3dly, by the vaporization of a little sulphuric 



acid, the greater part of which however remains united with 



the copper. 



RoasliTi^ of galena. 



Sulphuret of Galena is very difficult to desulphurate completely by 

 lead. roasting. The affinity of its component parts for oxigen, it 



is true, renders their separation sufficiently speedy ; but that 

 of the new compounds, sulphuric acid and "oxide of lead, 

 <nves rise to a new combination, which retains the sulphur, 

 and thus forms an obstacle to the desulphuration. To this 

 affinity of the oxide of lead for sulphuric acid must be 

 ascnbed the faciHty, with which this acid is foriried in the 

 roasting of galena.' \ 



I shall analyse in detail the various processes, to which 

 this import«At decornpo6ition has given birth, because I con- 

 ceive 



