218 On the De-sulphnration of Metals. 



Roasting of Pyritous Copper. 



We arrange pieces of pyritous copper upon faggots, in 

 such a way as to make the combustion continue along time. 

 The first application of the heat separates a part of the sul- 

 phur, which is distilled in some measure, and may be col- 

 lected ; but afterwards it is this combustible which serves, 

 upon burning, to continue the operation : sulphurous acid 

 is liberated, the elasticity of which, increased by the eleva- 

 tion of the temperature, hinders its combination with the 

 Wtiallic oxides. The sulphuric acid which is formed, iu 

 spite of the care taken to slacken the combustion, is united 

 to the oxides of copper and iron, but the sulphate of iron is 

 partly decomposed by the hyper-oxidalion of the metal. 



The pyrites of iron submitted to the same operation un- 

 dergoes unalogoiis decompositions, the succession of which 

 is in every respect the same. 



The roasting of pyritous copper in the reverberatory fur- 

 nace produces the same phainomena, and seems as if it 

 would admit of a much more conipleie separation of the 

 sulphur, than that produced in the open air. If it were not 

 so, it would no doubt be owing to the difficulty of hindering 

 the agglutination of the sulphuret produced by the elevation 

 of temperature, owing to the rapid and inevitable combus- 

 tiori of a great quantity of sulphur. 



I come now to speak of a furnace, in which we effect 

 at the same time both the melting and the roasting (to a 

 certain degree) of pyritous copper: this is the method prac- 

 tised at Falhun in Sweden*, and is done with an inner cru- 

 cible, 



• We find the following observations in the Foyages Melallargiques, by 

 Jars, tome iii. pages 55 & seq. " The flux of the mineral roasted a single 

 lime, is effected in a furnace which has an inner bason destined to contain 

 the produce of the operation." — " When it is heated, it i's charged with a 

 good deal of scorix from the flux of black copper, with quartz and a 

 little mineral," — " They do not mix the quartz with the mineral, but only 

 add it when there are any fears of mischief in the inner bason." — " The fusion 

 of the roasted pieces [matles) is effected in the same kind of furnace, but 

 smalkr." — " The substances must remain a longer time in the furnace, 

 which must not be opened until the end of twice twenty four hours. They 

 then extract a vorv few rich mattes, but a very large pig of black cop- 

 per." — " This method of melting the pyrites is certainly the only one that 



can 



