Effect of Temperature, Acidity, etc. 



407 



Table IV. 



Showing the percentage of pyrite obtained in synthetic products at observed 

 temperatures and acid concentrations. 



Temper- 

 ature 



Initial acid 



concentration 



in wt. % 



Final acid 



concentration 



in wt. % 



Average acid 



concentration 



in wt. % 



(x—a) iron 



dissolved in 



the Stokes 



reaction 



Percent- 

 age of 

 pyrite 



200° 



o-io 



1-14 



0-62 



7-77 



45 





•75 



1-35 



1-05 



8-23 



37 





1-00 



1--88 



1-44 



8-84 



27 





1-00 



1-73 



1-38 



8-75 



29 





1-25 



1-83 



1-54 



9-15 



22-5 





1-50 



1-78 



1-64 



9-41 



18-5 





1-75 



2-32 



2-03 



9'89 



11 





2-00 



2'50 



2-25 



10-27 



5 





2-00 



2-42 



2*21 



10*42 



3 





2-50 



3-00 



2-75 



8-94 



26 





2-75 



3-05 



2-90 



9-22 



21 



300° 



- o-io 



1-08 



0-59 



7-43 



49-5 





0-50 



1-20 



0-85 



7-71 



45-5 





1-00 



1-90 



1-45 



8-26 



37 





1-00 



1-90 



1-45 



8-30 



36 





1-50 



2*22 



1-86 



8-97 



25'5* 





1-50 



2-20 



1-85 



8-78 



28-0 





2-00 



2-38 



2-19 



9-31 



20-0 





2-00 



2-40 



2-20 



9-24 



21-0 





2-50 



2-50 



2-50 



8-96 



25-0 





2-50 



2-60 



2-60 



8-89 



26-5 





3-00 



2-84 



2-92 



9-42 



18*5 



* The time in this experiment was 7 days ; in all other experiments at 

 this temperature it was 1 day. 



natural marcasite when ground 1 h.+ and heated at 300° in 

 acid of 2'5 per cent saturated with hydrogen sulphide appeared 

 to contain 30 per cent to 40 per cent pyrite, judged by the 

 Stokes test. But further experiments showed that when mar- 

 casite was heated at 200° instead of 300°, or when the concentra- 

 tion of the acid was changed from 2'5 per cent to 2 per cent, a 

 similar change in the marcasite took place. Thus under con- 

 ditions (2 per cent H 2 S0 4 at 200°) where pure or nearly pure 

 synthetic marcasite was formed, natural marcasite appeared to 

 change, judging from the Stokes test alone. No correspond- 

 ing change in color was seen. Such products always floccu- 

 lated decidedly, a behavior which is probably accountable 



f Coarsely ground marcasite was unchanged when treated in this way. 



