GEOPHYSICAL LABORATORY. 157 



bornite, pyrrhotite, pyrite, sphalerite (ZnS), and galena (PbS). Except 

 for tetrahedrite and enargite, which may be set aside for the moment 

 on account of their chemical complexity, these are all of the important 

 minerals of the primary ores. The three most important constituents 

 of the enriching solutions are copper sulphate, ferrous sulphate, and 

 sulphuric acid, all formed by the surface oxidation of the sulphides in 

 the air. The effect of these three constituents, singly and in various 

 combinations, on the aforementioned sulphides has now been studied. 

 The reactions are very slow at the temperature of the earth's surface, 

 at or near which they proceed; so slow that a number of previous 

 attempts to discover them in the laboratory have failed utterly. Our 

 preliminary work was therefore done at 200°, with the sulphide finely 

 powdered to increase the reacting surface, and with solutions of low 

 concentration. The containing vessels were of quartz glass. In this 

 way, with the material aid of the microscope for the diagnosis of the 

 products, the quantitative relations between the solutions and sul- 

 phides at this temperature were worked out. 



With knowledge gained in this way it has been possible to interpret 

 results at lower temperatures. Experiments were made at 100° and 

 at 40°. Those at 40° required from 1 to 2 months for each experiment 

 and the use of mechanical shakers running continuously, which kept 

 the powdered sulphide suspended in the liquid and thus continually 

 exposed to its action. 



Summarizing the results of this action of the enriching solutions on 

 the sulphides : copper sulphate alone changes them all eventually into 

 chalcocite, i. e., copper precipitated from the solution and the copper 

 in the sulphides both take that form as the end-product. The course 

 of the reaction varies with different sulphides. The simple sulphides 

 sphalerite and galena first give covellite (CuS) chiefly, as if there were 

 a simple interchange of the metals 



ZnS + CUSO4 = ZnS04 + CuS 



But covellite itself is slowly changed to chalcocite by copper sulphate. 

 In this rather curious reaction copper sulphate appears as an oxidizing 

 agent, removing half the sulphur from the sulphide as sulphuric acid 



5CuS+3CuS04=4Cu2S+4S03 

 Indeed, in its action on the other sulphides, copper sulphate behaves 

 as an oxidizing agent, changing the iron to ferrous sulphate and the 

 sulphur in part to sulphuric acid. 



Pyrrhotite shows rather unique behavior with copper sulphate in 

 that the first product is chalcopyrite. But since chalcopyi'ite is 

 changed finally to chalcocite, so pyrrhotite, if subjected to the action 

 of copper sulphate for a sufficientlj^ long time, gives chalcocite. 



Ferrous sulphate solution in the presence of copper sulphate undoubt- 

 edly accelerates enrichment. It is surmised that the cause of this 



