EXTRACTION OF COPPER. 47 



New 3IetJiod of Reduction from Copper-pyrites. — In Rivot 

 and Philipps's method, the pyrites is roasted to oxidize the 

 greater part of the sulphurets, the roasted ore fused in a re- 

 verberatory with silicious matters, lime, and fine coal, to con- 

 vert the oxide of copper into a silicate, — and metallic cop- 

 per precipitated from the fused mass by dipping in iron rods. 

 After 3-4 hours the slag is said to retain only 0.4—0.6 of one 

 per cent, copper, and the iron bars lost 1-6 kilogr. for 12-42 

 kilogr. of copper obtained. On this process, Eisner remarks 

 that it is the method of precipitation long since adopted with 

 lead-ores, and he corrects the chemical explanation. For in 

 roasting such pyrites, part of the sulphur passes off as sul- 

 phurous acid, and part remains, forming sulphates of the 

 oxides of iron and copper, mixed with some unaltered pyrites. 

 In the subsequent fusion there is formed protosilicate of iron 

 and lime, and copper-stone, or impure sulphuret of copper ; 

 from which last, the metallic iron precipitates copper while it 

 is converted into sulphuret of iron. (For a detailed account 

 of this method, see Journ. Fr. Inst. (3) xvii. 60.) 



Fluxing. — Considerable difficulty being often experienced 

 in fluxing refractory copper-ores, many substances have been 

 proposed to facilitate their fluxion, such as sulphate or car- 

 bonate of baryta, to which a recent patent adds galena. (Lond. 

 Journ. Oct. 1850.) 



Extraction of Copper. — Mitchell, Alderson, and Warriner 

 have patented a process (Ch. Gaz. vii.) for extracting copper 

 from ores by one, or, at most, two roastings and fusions. It 

 is applicable to sulphurets alone, or mixed with oxide, car- 

 bonate, and sulphate, or with sulphurets of other metals. The 

 fiinely-powdered ore is calcined in a reverberatory furnace, and 

 well stirred during the operation in order to promote oxida- 

 tion. After cessation of sulphurous acid vapors, the heat is 

 to be increased, but not high enough to agglutinate the mass. 

 In this way all sulphate of copper, which may have been 

 formed, is decomposed. If magnesia is present, the hot ore 

 must be raked into water and leeched for the separation of 

 magnesia salt. 



