Determination of Pyriie and Marcasite. 



387 



cation of the method to synthetic mixtures, which has been the 

 object of the present investigation. 



(a) Independence of the chemical action of the two sulphides. 

 — Since the quantity of iron which dissolves in the Stokes 

 reaction is approximately a linear function of the composition 

 of the sulphide mixtures, each sulphide in the mixture behaves 



Fig. 4. 



100 



90 



80 



70 



C 60 



a) 



•GO 

 CD 

 +-> 



C 



a) 

 o 



i_ 



8. 



50 



40 



30 



20 



10 



^ 



5 





A 



V 



^ 

 \ 



S 



\ 



to 



X 



v 



so 



s 



> 



\ 



V 



\ 



-S 



V 



^_ 



4 5 6 7 8 9 10 II 



Dissolved iron in terms of standard permanganate soltifon 



Fig. 4. Iron dissolved from pyrite-marcasite mixtures by a standard 

 ferric solution. Pyrite from Elba ; marcasite from Joplin, Mo. 



with the solution practically as it does when alone. The iron 

 which dissolves comes only from decomposed sulphide, conse- 

 quently in a sulphide mixture the quantity of each decomposed 

 is directly proportional to its percentage in the mixture. Thus 

 in a 50 per cent mixture, one half as much of each mineral is 

 decomposed as when each reacts alone with the solution. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 227.— November, 1914. 



27 



