On the Desulphuration of Metals. 81 



composed at a high temperature. 2d. This decomposition 

 gives place to the formation and to the disengagement of a 

 great quantity of sulphurous acid, and consequently to the 

 separation of a considerable portion of the sulphur contain- 

 ed in the ore*. 3d. The result is oxide of lead, when the 

 proportions are proper ; and in the contrary case a mixture of 

 oxide and of sulphat, or oxide and galena. The application 

 of these consequences to the roasting of the sulphuret of 

 lead in this reverberating furnace is very easy. I shall explain 

 the theory of this operation in the way I conceive it. 



The pulverized galena, or the schlich of lead, spread out 

 upon the floor of the furnace in a layer of a few inches in 

 thickness, the upper part of which is exposed to the action, 

 produces the phsenomena usually observed in the common 

 roastings. The heat vaporises a little sulphur ; the air 

 converts that part upon which it acts into sulphurous acid, 

 which is liberated ; but a much greater part is converted into 

 sulphuric acid, which is combined with the lead oxidized at the 

 same time. The ores are stirred ; the sulphate of lead is mixed 

 with theundecomposed schlich, and their decomposition pro- 

 duces sulphurous acid ; the surface of the layer which has 

 been renewed, reproduces sulphate, which afterwards serves 

 to produce a new disengagement of gas, and thus continues 

 the desulphuration, to which we find there is no end except 

 the complete decomposition of the galena. If the operation 

 has been well managed, and if too much sulphate of lead 

 has not been formed, the result of the roasting will be al- 

 most pure oxide of lead ; in the contrary case, some sul- 

 phate will probably remain, which charcoal will bring * 

 back, to the state of sulphuret, and the decomposition of 

 which will take place like that of the galena. We may 

 judge from this detail, how important it is to avoid melting 

 the sulphuret of lead subjected to roasting j for the action 

 of the air upon the melted ore will soon be rendered null by 



* If we admit that a mixture of one part of sulphuret and two of sul- 

 phate are entirely decomposed and reduced to oxide of lead, the quan- 

 tity of sulphur separated will be two-fifths: so that one part of sulphate, in 

 an indefinite quantity of galena, will separate one-fifth of sulphur; and one 

 V «f sulphuret in sulphate will separate three-fifths. 



Vol. 32. No. 125. Oct. 1808. F the 



