Determination of Pyrite and Marcasite. 



377 



In some instances, for some unknown reason, the solution 

 would fail to wet the sulphide satisfactorily, and the results 

 would then be unsatisfactory. 



(a) Explanation of the low results with pure marcasite. — 

 The abnormal results for the sulphide mixtures low in pyrite 



Fig. 2. 



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4 5 6 7 8 9 10 II 



Dissolved iron in terms of standard permanganate solution 



Fig. 2. Stokes' results on iron dissolved (x— a) from pyrite-mareasite 

 mixtures by a standard ferric sulphate solution. The values for as are cal- 

 culated from Stokes' published values for p, the percentage of sulphur 

 oxidized. 



are very well accounted for, as we have seen, on the supposi- 

 tion that the reactive surface of the marcasite is reduced by 

 flocculation. In mixtures which contain 25 per cent or more 

 of pyrite, flocculation rarely if ever occurs. Marcasite alone, 

 however, gives somewhat too low results for the iron dissolved 



