On (he De-sitlphuration of Metals. 217 



new chemical theories have remarked the inflLience of the 

 atmospheric air, have never regarded it as essential*. The 

 experiments 1 have detailed having shown how the action 

 of heat alone is insufficient for decomposing a metallic sul- 

 phuret, we must necessarily ascribe to the oxygen of the 

 atmosphere the greatest share in the de-sulphuration of the 

 inelals by roasting. The affinities of sulphur and of me- 

 tallic substances for this principle render this assertion very 

 probable; it is besides proved by the chemical examination 

 of the produce of all the roasting, as well as by the way in 

 which the operation is conducted. In place of seeing in the 

 roasting of the sulphurets the volatilization of the sulphur, 

 produced Ly a well managed heat, it will be the decompo- 

 sition of a sulphurct by the simultaneous action of the air 

 and of caloric : and the well known necessity of not melting 

 the ores does not seem to be recommended in consequence 

 of the fear of coinnnmicating to it, together with liquidity, a 

 force of cohesion which will oppose the separation of the 

 sulphur; but rather because this state will confine the ac- 

 tion of the air to a surface, which, not being capable of 

 being renewed, will be soon covered by the metallic oxide. 

 The combination of the oxviien with the elements of the 

 sulphurets, gives birth to oxidts and to acids, the affinities 

 of which have great influence upon the separation of the 

 sulphur, and the results of a roasting : the latter generally 

 present a rnixture of oxide, of sulphate, and of indecomposed 

 sulphurel. I shall examine separately and in detail the roast- 

 ing of several kinds of sulphurets, because the nature of the 

 metal produces great modifications in their results ; and shall 

 presently show, why, and in what form, the sulphur is se- 

 parated. 



• Macquer, in this respect, agrees with the metallurpisfs. We find in 

 his Dictionary of Chemistry the following passage: '' There are several 

 methods of separating sulphur from metallic substances : in the first place, as 

 (ulphur is volatile, and a» these substances arc fixed, or at least not so volatile 

 as sulphur, the action of heat alone is suJjicieiU to take the sulphur from most 

 metals." He "^eems, however, to have been aware of the importance of the 

 contact of the atmospheric air in roasting, since he says, when spe.iking of 

 the sulphurets of mercury and of arsenic, " It will be possible to desulphu- 

 rate thetn without iatermedium, by a wtil -managed heat and in the open air." 



Rous tin n 



