216 On the De- sulphur ation of MelaU. , 



sidue was of a metallic lustre ; it was agglutinated, and did 

 not contain an atom of ductile lead *. 



The heal not having been very strong in this experiment, 

 I submitted 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 plomb by the French metallurgists; jthere 

 was no lead free from sulphur, but only some parts of the 

 button were a little ductile. Analysis convinced me that there 

 remained about three fifths of the sulphur contained in 

 the galena. I attributed a part of the loss of 27 per cent., 

 which it had undergone by the action of the fire, to the vo- 

 Jatilization of tlie sulphuret of lead itself; for the loss 

 owing to the separation of the sulphur could not exceed six 

 per cent, at most. 



The galena therefore undergoes but a very incomplete de- 

 composition from heat. 



I shall not particularize the sulphurets of zinc, antimony, 

 &c., because I do not know a sufficient number of experi- 

 ments for determining, 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 ^lone upon the metallic sulphu- 

 rets, apd particularly upon those of iron, copper, and lead, 

 is confined to their taking 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 atmosphe- 

 ric Air, upon the metallic Sulphurets. 

 The metallurgic operation which has for its object the 

 de-sulphuration of the metals is known by the name of 

 roasting. Most of the authors who have spoketi of it do 

 not seem to have recognized any other agent in the de- 

 composition except caloric ; and even those who since the 



* There are few chemists who have not made this experiment with similar 

 results. I may here remark, that if the heat had been long enougji con- 

 tinued, and in the open air, the galena would have been completely roasted. 



