DESULPHURATION OF METALS. £05 



ever, tlmt the pi-oportion of one part of galena to two of sul- sulpliate 2 



1 T 1 1 -1 •. j-rr would produce 



phate will be very near the mark ; and besides it ditters ^ decomposi- 

 littie from what a calculation of their component parts t^^/^- 

 would indicate. 



The followiiiir are the natural consequences of these facts : Conclusions^. 

 ], Galena and sulphate of lead mutually decompose each 

 other at a high heat. 2, This decomposition gives rise to the 

 formation and evolution of a large quantity of sulphurous 

 ax'id, and consequently to the separation of a considerable 

 portion of the sulphur contained in the ore. 3, The result 

 is oxide of lead, when the proportions are suitable; and 

 when. otherwise a mixture of oxide and sulphate, or oxide 

 ? and galena. 



>. .^ The application of these consequences to the roastinar of ''^^^^''5^ ^^ , 

 ■ , r. 1 1 • 1 1 n • T roasting galea* 



sulphuret ot lead in the reverberatory furnace is easy. 1 in the reverbe^ 



shall explain the theory of this process in the manner in ratory furnace* 

 which I conceive it. The powdered galena, or washed ore 

 . of lead, spread on the bottom of the furnace to the thickness 

 of a few inches, the upper part of which is exposed to the 

 action of the air, gives rise to the phenomena we have ob- 

 served in ordinary roastings. The heat vaporizes a little sul- ^ 

 phur: the air converts part of that on which it acts into sul- 

 phurous acid, which is evolved, and another more consic^^ra- 

 * ble into sulphuric acid, which combines with the lead oxided 

 at the same time. The ore is stirred : the sulphate of lead 

 mixes witk that which is not decomposed, and their mutual 

 decomposition produces sulphurous acid : the fresh surface 

 reproduces sulphate, which serves to occasion a fresh extri^* 

 -cation of giis, and thus to continue the desulphuration, 

 which is limited only by the complete decomposition of the 

 galena. If the process have been well managed, and too 

 much sulphate of lead has not been formed, the result of the 

 roasting will be almost pure oxide of lead : if the contrary, 

 some sulphate may remain, which the charcoal will reduce to 

 the state of sulphuret, and the decomposition of which will 

 be ejected in the same way as that of so much galena, 

 Jlence we may learn the importance of not fusing the sul- 

 phuret of lead subjected to the process of roasting; for the 

 action of the air on the fused ore would soon be rendered 

 null by the formation of oxide of lead which would cover it, 



and f 



