8 J- On the Desulphuration of Metals. 



and the sulphur is separated more or less completely in the 

 state of sulphurous acid. 



§ III. Desulphuration of the Metals independent of the Action, 

 of the Air. 



The varied affinities of sulphur for different mineral sub- 

 stances, furnish the means of decomposing certain sul- 

 phurets ; and several have been employed in metallurgy 

 with success. In order that the decomposition of a metallic 

 sulphuret by any mineral should form the basis of a metal- 

 lurgic process, it is not sufficient that the affinity of this 

 mineral for sulphur should be greater than that of the metal; 

 it must, besides the conditions required by ceconomy, also 

 possess several other requisites absolutely necessary for the 

 success of the operation, which considerably limit the num- 

 ber of the agents pointed out by chemistry : for instance, if 

 the sulphuret resulting from the decomposition is not fusible, 

 or but very little so, if it has the property of combining 

 with the metal required to be separated, or rather with the 

 still undecomposed sulphuret, it is evident that we cannot 

 effect our purpose, namely, the isolation of the metallic 

 substance. Hitherto little else has been used except lime 

 and iron. 



Desulphuration of Mercury. — It is very easy to decom- 

 pose the sulphuret of mercury; it being sufficient if we 

 present to the sulphur a substance capable of retaining it, 

 and volatilize the mercury alone. It is thus that iron and 

 lime are employed together or separately in the treatment of 

 the ores of cinnabar. 



Desulphuration of Copper. — Pyritous copper is melted in 

 some foundries with lime, either in the common or in the 

 reverberating furnace ; but the process is not well enough 

 known as yet to enable us to judge of the efficacy of lime as 

 an agent in this case. 



I was once of opinion, with some metallurgists, that the, 

 well-known superior affinity of iron for sulphur over that 

 of copper for the same combustible, might determine the 

 decom position of the sulphuret of copper by this metal, at least 



in 



