380 Allen and Crenshaw — Stokes Method for the 



from any cause, the results will be unsatisfactory for mixtures 

 containing less than 25 per cent pyrite. Ignorance of this 

 fact cost us much time in one stage of our work. 



2. Results on mixtures of the natural minerals. — When the 

 above precautions were carefully followed, we obtained the 



Fig. 3. 



100 



90 



80 



70 



60 



5Q 



40 



30 



20 



10 



A 



A 



t 



°v 



\ 



^r 



V 



x^ 





v 



t 





s 



\ 



A 



V 





3 



- V 



1 — I — I — 1 — 1 — 1 — 1 — I — I — L_J — 1 — 1 « i> 1 



4 5 6 7 8 9 10 fl 



Dissolved iron in terms of standard permanganate solution(.rv7) 



Fig. 3. Iron dissolved (x — a) from pyrite-marcasite mixtures by a 

 standard ferric sulphate solution. Revised results, oo Results obtained by 

 shaking with quartz, xx Results obtained without quartz. The pyrite was 

 from Roxbury, Conn.; the marcasite from Joplin, Mo. 



results given in Table II and graphically presented in fig. 3. 

 It is evident that we have here a sensibly linear relation be- 



tween the iron dissolved and the composition of the mixtures 



