481 
Desulphur cition of Metals . 
The heat not having been very strong in this experiment, I sub- 
mitted to the fire of a forge some pulverized galena, placed in a 
crucible, and covered with charcoal in powder. I found a mass 
which had been melted, and similar to what is called matte de 
filomb by the F rench metallurgists ; there was no lead free from sul- 
phur, but only some parts of the button were a little ductile. Ana- 
lysis convinced me that there remained about three fifths of the 
sulphur contained in the galena. I attributed a part of the loss of 
2 7 per cent, which it had undergone by the action of the fire, to the 
volatilization of the sulphuret of lead itself; for the loss owing to 
the separation of the sulphur could not exceed six per cent, pit 
most. 
The galena therefore undergoes but a very incomplete decom- 
position from heat. 
I shall not particularize the sulphurets of zinc, antimony, Sec. 
because I do not know a sufficient number of experiments for de- 
termining, in a certain manner, the effects which heat produces 
upon them : analogy, however, inclines me to think that it does not 
completely decompose them. 
All the facts I have presented seem to me to establish, that the 
action of caloric alone upon the metallic sulphurets, and particu- 
larly of those upon iron, copper, and lead, is confined to their tak- 
ing from them a small portion of the sulphur which they contain, 
and afterwards in melting and volatilizing them. 
§ II. Of the simultaneous Action of Heat , and Atmospheric Ah' 
upon the metallic Sulphurets. 
The metallurgic operation which has for its object the de-sul- 
phuration of the metals is known by the name of roasting. Most 
of the authors who have spoken of it do not seem to have recog- 
nized any other agent in the decomposition except caloric ; and 
even those who since the new chemical theories have remarked 
the influence of the atmospheric air, have never regarded it as es- 
sential*. The experiments I have detailed having shewn how the 
action of heat alone is insufficient for decomposing a metallic sul- 
phuret, we must necessarily ascribe to the oxygen of the atmos- 
phere the greatest share in the de-sulphuration of the metals by 
roasting. The affinities of sulphur and of metallic substances for 
* Macquer, in this respect, agrees with the metallurgists. We find in his 
Dictionary of chemistry the following passage : “ There are several methods 
ef separating sulphur from metallic substances : in the first place, as sulphur 
