1865.] MACFARLANE — EXTRACTION OF COPPER. 221 



chloride. The latter is condensed and treated further. This 

 process labors under the same disadvantage as Longmaid's with 

 regard to copper in the residues. 



Among the various processes just enumerated, those which are 

 most advantageous in economical respects, and which are best 

 suited to the local circumstances of Canada, are evidently those in 

 which few or no extraneous substances are required to render the 

 copper soluble, and in which the acid necessary to form the solu- 

 ble salt of copper is derived from the oxidation of elements pre- 

 sent in the ore itself. At first sight the simplest and pos.>ibly 

 most efficient means of rendering the copper soluble would appear 

 to be that of merely calcining the sulphuret ores and lixiviating 

 the product. Almost all such ores, whether containing copper glance, 

 purple copper, or copper pyrites, certainly yield by such treat- 

 ment more or less of their copper in a soluble state ; but the amount 

 of the metal so yielded in proportion to the quantity contained in 

 the ore, is invariably very small indeed. Even with ores which 

 contain a very considerable excess of sulphur, the calcination must 

 be very carefully conducted if the extraction is at all to approach 

 completeness. In the first stage of calcination sulphurous acid is 

 given off; in the second sulphate of iron is formed ; during the 

 third stage it is necessary to heat the charge rather strongly in 

 order to decompose the sulphate of iron, and transfer its sulphuric 

 acid to the oxide of copper. In so doing there is a danger of too 

 much heat being applied, and even of the sulphate of copper 

 being decomposed. It is therefore extremely difficult to regulate 

 this process, and the disadvantages of its being performed at too 

 low a temperature consist not only in the extraction being imper- 

 fect, but also in the deposition of basic salts of iron while the cop- 

 per is being precipitated. In this way the latter becomes so con- 

 taminated that many specimens of copper produced by cementation 

 do not yield by assay over. 60 per cent of the pure, metal. 



These disadvantages are to a very great extent removed by the 

 use of common salt. By its action the sulphate of iron first formed 

 is decomposed at a low temperature, and sulphate of soda and 

 chloride of iron produced. The latter seems to be easily decom- 

 posed, and its chlorine transferred, in part at least, to the copper. 

 On treating the calcined product with water, a solution is obtained 

 which is very pure, often containing merely a trace of iron, in 

 Which case the deposition of basic iron salts becomes impossible. 

 But although common salt may remedy the defects here indicated, 



