376 Allen and Crenshaw — Stokes Method for the 



Table I. 



Stokes 1 values for x, the total iron in solution, and (x—a), the iron dissolved 

 from pyrite-marcasite mixtures by ferric sulphate solution. 



Percent 

 Pyrite 



p— percentage of sulphur 



oxidized (experimentally 



determined) 



x cal. from p 

 by equation 



(2) 



(x — a) (the iron 

 dissolved) 

 a = 36-71 



100 



60-5 



40*68 



3-97 



95 



52-9 



41-11 



4-40 



90 



48-9 



41-38 



4-67 



80 



40*3 



42-08 



5-37 



60 



29-0 



43-41 



6-70 



40 



22*3 



44-58 



7-87 



20 



17-1 



45-78 



9-07 



10 



15-2 



46-33 



9-62 



5 



16-0 



49-09 



9-38 







18-0 



45-54 



8*83 



one which proved of any value was to shake the ferric solution 

 and sulphide together with coarsely powdered quartz* and 

 beads by means of which the lumps of sulphides were thor- 

 oughly ground up. Some details may make the operation 

 clearer to the reader. The 500 cc boiling flask used in the oxi- 

 dation experiments was fitted to a rubber stopper through 

 which passed the reflux condenser (the cooling jacket of which 

 was 20 cm in length) and a glass tube reaching to the bottom of 

 the flask through which the carbon dioxide entered. 250 cc 

 standard ferric alum solution with 2 g. quartz and about fifty 

 beads of Jena glass were then added. The solution was now 

 freed from air by boiling for ten minutes in the stream of car- 

 bon dioxide, and then cooled for fifteen minutes while the gas 

 was still passing. Stokes' device for introducing the sulphide 

 was used, viz., a small glass bucket suspended above the liquid 

 by a platinum wire which passed up through the condenser. 

 After the sulphide had been purified and dried for an hour in 

 a vacuum desiccator, as shown farther on, it was quickly 

 removed and poured into the bucket, the bucket attached to 

 the platinum wire, and the flask again closed. The solution 

 was now brought to boiling, while the bucket remained sus- 

 pended above the liquid. Finally the bucket was dropped by 

 drawing out the wire and the flask vigorously rotated for five 

 or ten minutes, or until the powder seemed to fill the liquid 

 and so remained, neither floating on the surface nor sinking to 

 the bottom. The boiling was continued for two hours, when 

 the ferric iron should be entirely reduced. 



* This quartz contained only 04 per cent of oxides other than silica. 



