ARTIFICIAL FORMATION OF CHALCOCITE 273 



writer and carried on by Messrs S. J. Gormly and C. F. Tohnan in the 

 laboratories of the Anaconda Copper Mining company. 



The first experiments were conducted with a relatively small amount 

 of cupriferous pyrite and a dilute solution of copper sulphate. The 

 results, as reported, show the formation first of SO2 and then of HjSO^; 

 the solution of both copper and iron and the precipitation of the iron 

 as ferric liydrate, and the formation of copper sulphide. 



Analyses of the mine waters showed no ferrous salt in the strong " cop- 

 per water," but disclosed the presence of quantities of cuprous salts, in 

 acid solution. 



The experiments repeatedly showed that SO2 is formed by the action 

 of pyrite and chalcopyrite upon CuSO^, and that the SO2 reduces some 

 of the copper ions of the CuSO^ to the cuprous form. According to theo- 

 retical chemistry, a relatively insoluble compound may be precipitated 

 by very small amounts of a salt containing one of the ions of the insol- 

 uble compound, if a large amount of the salt containing the other ion is 

 present. To test this, a solution of copper sulphate was treated with the 

 sulphides of arsenic, lead, copper, iron, zinc, and with p3^rite ; and in 

 each case copper sulphide was precipitated, proving that these sulphides 

 may precipitate copper sulphides from a solution of a copper salt. It 

 is probable also that the more insoluble the precipitating sulphide, the 

 more concentrated must be the solution of copper sulphate. 



To produce a solution containing cuprous ions, the above-mentioned 

 sulphides were treated with a solution of copper sulphate (CuSO^) and 

 SO2, and precipitates were formed in each instance. An analysis of the 

 precipitate formed by copper sulphide showed a precipitation of 12 per 

 cent of the weight of the original CuS as CU2S, indicating the formation 

 of chalcocite under these conditions. 



It was not ascertained whether the iron salts will reduce enough copper 

 to form CugS in presence of pyrite or other sulphides, or whether the 

 SO2 formed by solution of the pyrite and other sulphides is the active 

 agent. 



Knowing full well that it might be urged that the formation of a pre- 

 cipitate of a certain chemical composition is quite a different matter 

 from the production of a mineral having the same composition, the ex- 

 periment now about to be briefly described was undertaken and carried 

 to completion with exceedingly gratifying and satisfactory results. 



In a slightly acid solution containing sulphurous anhydride (SO2) 

 was digested pyrite (FeSj) at ordinary temperature and pressure for 

 three months. The pyrite taken was ordinary "jig concentrates," about 

 one-fourth of an inch in diameter, from the Parrot concentrator at Butte, 

 and of the following composition : 



