485 
Be sulphur at ion of Metals. 
The reverberating furnace may be employed with great suc- 
cess in roasting the sulphurized ores of lead. In some foundries, 
they produce in this kind of furnace so complete a separation of 
the sulphur, that it is sufficient, when the roasting is supposed to 
be finished, to add some charcoal, in order to obtain instantaneous- 
ly a great quantity of metallic lead. It cannot be doubted, however, 
that a great quantity of sulphate of lead is formed ; which, as we 
have already seen, is a necessary result of the action of the air 
upon galena exposed to a high temperature ; the chimneys of the 
furnaces are likewise filled with the above substance : the decom- 
position of this sulphate by charcoal produces a sulphuret or a 
matte of lead ; and although sulphurous acid may be disengaged, 
it is very difficult to explain why the addition of charcoal makes 
the lead flow instantly in a considerable quantity. I thought that 
the sulphate of lead was decomposed during the roasting, and that 
nothing remained after this operation, but an oxide a little mixed ; 
and I thought I discovered the cause of this decomposition in the 
action of the galena, as yet undecomposed, upon the sulphate form- 
ed. The following experiments will show the nature and result 
of this action. 
I put into a retort a mixture composed of one part of pulveri- 
zed sulphuret of lead, and three of sulphate*, and I heated it at first 
but slowly. When the retort was red-hot, a considerable disen- 
gagement of sulphurous acid gas took place which lasted an hour, . 
when the retort melted ; the residue presented a mixture of ox- 
ide and of sulphate of lead. I ascertained that the sulphurous 
acid which had been collected in the water was not mixed with 
sulphuric acid. 
This experiment demonstrates in an indisputable manner the 
decomposition of the sulphate of lead by the sulphuret, or rather 
that of the sulphuric acid which it contains, by the sulphur and the 
lead of the galena. The sulphurous acid certainly proceeds both 
from the oxygenation of the sulphur, and from the demi-decompo- 
sition of the acid, as I am convinced that no sulphate remained in 
the residue. I repeated this decomposition, employing equal parts 
of galena and of sulphate; the sulphurous acid disengaged was 
more abundant, and there remained in the retort a mixture of 
oxyd and of sulphuret ; from which I concluded, that if, in the 
first experiment, the proportion of sulphuret of lead was too weak, 
*■ This mixture was made in the humid way 
