Determination of Pyrite and Marcasite. 



375 



deviation in the line indicated that, in those mixtures where it 

 occurred, the surfaces of the two minerals were no longer pro- 

 portional to their weights. There was in fact some positive 

 ground for this view, since it had already been noted by Stokes 

 that marcasite was inclined to flocculate during the oxidation 



Fig. 1. 



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Dissolved iron interms of standard permanganate solution 



Fig. 1 . Curve showing iron dissolved from pyrite-marcasite mixtures by 

 a standard ferric solution. (Former results.) 



tests. Flocculation would of course reduce the surface of the 

 finely powdered marcasite, and if the pyrite were unaffected, 

 the results would indicate too much pyrite, which as the reader 

 may see, is exactly the direction of the errors in figs. 1 and 2. 

 Many ways were tried to obviate the difficulty, but the only 



