420 H. N. Stokes — Pyrite and Marcasite. 



pyrite and 100 per cent for marcasite. The relative amounts 

 of ferrous and ferric salts depend simply upon the establish- 

 ment of equilibrium between the solution and the decomposi- 

 tion products of the pyrite and marcasite, not upon any 

 fundamental difference in the minerals themselves, and the 

 hypothesis in question, while possibly true, is thus far devoid 

 of a valid experimental basis. 



As part of an investigation of the reactions involved in the 

 secondary deposition of copper by sulphides, it may be men- 

 tioned that cupric chloride at 200° decomposes pyrite according 

 to the equation 



FeS 9 + 14CuCl s + 8H JI 0=14CuCl+FeCl s +12HCl + 2H s S0 4 . 



Sulphuric acid is also formed by the action of cupric chloride 

 on cupric sulphide and apparently from pyrite and cupric sul- 

 phate, so that the oxidation of sulphur appears to be a 

 necessary part of the reaction when certain sulphides are acted 

 on by cupric salts. These reactions, with other salts and sul- 

 phides, are still under investigation. 



