487 
De sulphur ation of Metals. 
the upper part of which is exposed to the action, produces the 
phenomena 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 oxydated at the same time. The ores are stirred ; 
the sulphate of lead is mixed with the undecomposed schlich, and 
their decomposition produces sulphurous acid; the surface of the 
layer which has been renewed, reproduces sulphate, which after- 
wards 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 opera- 
tion has been well managed, and if too much sulphate of lead has 
not been formed, the result of the roasting will be almost pure 
oxyd of lead ; in the contrary case, some sulphate will probably re- 
main, which charcoal will bring back to the state of sulphuret, 
and the decomposition of which will take place like that of the ga- 
lena. We may judge from this detail, how important it is to 
avoid melting the sulphuret of lead subjected to roasting; for the 
action of the air upon the melted ore will soon be rendered null by 
the formation of the oxyd of lead which will cover it ; and the 
sulphate of lead not being capable of being any longer mixed with 
the galena, there will be no method left of desulphuration. 
The roasting of galena in the reverberating furnace is therefore 
reduced to the conversion of the sulphur which it contains into 
sulphurous acid ; and as it is produced in a great measure by the 
intermedium of the sulphate of lead which is continually formed, 
this process admits of a much more complete desulphuration than 
the others. 
The same decomposition of the sulphuret bf lead by the sul- 
phate, in my opinion, takes place also in the treatment of the ores 
of lead in what are called Scotch furnaces : in Scotland they roast 
and melt galena by one uninterrupted operation, employing coal 
and turf. 
This kind of furnace is employed with success in the mine af 
Pezey, in melting roasted galena containing at least one-third of 
its weight of sulphate of lead. It gives no mattes as a final result, 
which proves that it admits of the decomposition of the sulpha! 
and the separation of the sulphur contained in it. I am of opinion 
that the action of the portion reduced to the state of sulphuret by 
