486 
De sulphur ation of Metals . 
it was too strong in the latter. I also made another attempt ta 
attain some proportions rigorously sufficient for the mutual de- 
composition, and endeavoured at the same time to assure myself 
of the oxydation of the lead contained in the galena in a metallic 
state. I put fourteen grammes of sulphate, well mixed with 
eight grammes of sulphuret, in a crucible, which I allowed to be- 
come red-hot in a gradual manner. I remarked that a consider- 
able crackling was produced, occasioned by the disengagement 
of the sulphurous acid. I did not take the crucible from the fire 
until I saw its contents melted. I found two substances well se- 
parated ; the one occupying the bottom of the crucible was merely 
melted sulphuret of lead, without any mixture of ductile lead ; the 
other presented all the characters of the oxyd of lead called glass 
of lead ; this part was a combination of oxyd and silex , proceed- 
ing from the materials of the crucible, without any marks of sul- 
phate of lead. 
This experiment proved that the lead of the galena was oxy- 
dated at the expense of the sulphuric acid ; but it did not show 
the quantity of galena necessary to the complete decomposition of 
the sulphate. I am of opinion, however, that the proportion of 
one part of the former to two of the latter is sufficient ; besides, 
it closely resembles the proportion which calculation gives us of 
the composition of these substances. 
The following are the natural consequences of these facts : 
1st. The galena and the sulphat of lead are mutually decom- 
posed at a high temperature. 2d. This decomposition gives 
place to the formation and to the disengagement of a great quan- 
tity of sulphurous acid, and consequently to the separation of a con- 
siderable portion gf the sulphur contained in the ore.* 3d. The 
result is oxyd of lead, when the proportions are proper ; and in 
the contrary case a mixture of oxyd and of sulphat, or oxyd and ga- 
lena. 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 schlick of lead, spread out up* 
on the floor of the furnace in a layer of a few inches in thickness, 
* If we admit that a mixture of one part of sulphuret and two of sulphate 
are entirely decomposed and reduced to oxyd or' lead, the quantity 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. of sulphuret in 
sulphate will separate tbvee-finhs. 
