386 Allen and Crenshaw — Stokes Method for the 



Tarle III. 

 Showing the Stokes Constant for Different Pyrites and Marcasites. 



Mineral. 



Locality. 



x — a 



Impurities. 



Pyrite 



Leadville, Col. 



3-95 



0'1 per cent of copper. 



a 



Elba, No. 1 



4-17 

 4-20 



none found except -04 per 

 cent quartz. 



it 



Elba, No. 2 



4-35 



- 04 nickel and cobalt — 



it 



" " after heating 

 with sulphuric acid at 200° 



4-18 



mostly the latter, ferric 

 oxide suspected. 



(( 



Eoxbury, Conn. 



4-46 



1*4 per cent arsenic. 



(< 



Synthetic, prepared by heat- 

 ing synthetic marcasite 



4-14 

 411 



10-57 





Marcasite 



Joplin, Mo. 



10-58 

 10-52 



only quartz found 



c< 



Galena, 111. 



10-57 





li 



* Synthetic at 25° 



10-20 

 10-34 



may contain pyrite 





" 200° 



10-27 

 10-42 



n <( tt 





" 300° 



10-20 

 10-34 



" 



* See this Journal, The effect of temperature and acidity in the formation 

 of marcasite and wurtzite, (4), xxviii, 411, 1914. 



sulphide, the value of the Stokes constant agreed with the 

 purest pyrite. The hematite had evidently been removed by 

 the treatment. The Roxbury pyrite which was used for the 

 most part in the present work was selected on its macroscopic 

 appearance, the higher results being at iirst regarded as more 

 accurate. Later, when the lower results with synthetic pyrite 

 had thrown them under suspicion, an analysis showed the pres- 

 ence of arsenic. Stokes found that arsenopyrite gave high 

 results; 1 per cent arsenic in that form having the same effect 

 in the Stokes test as 2 per cent marcasite, while it may be seen 

 from the table that 1*4 per cent arsenic in the Roxbury pyrite 

 has the same influence as 4 per cent marcasite. 



5. Linear relation between any pyrite and any marcasite. — 

 It is important to note in this connection that the constants of 

 any pyrite and marcasite are additive in their mixtures. Thus a 

 number of tests showed this to be true of the Elba pyrite No. 

 2 and the Joplin marcasite, while more numerous experiments 

 (see fig 4) show the same thing for the Joplin marcasite and 

 Elba pyrite No. 1. This is a fact of importance in the appli- 



