Brown.] 



236 



[May 18, 



I. Table Showing Average Relative Oxidation of Sulphur in Pyrite and 

 Marcasite by Solutions of KMnO^ at 2SP and at 100°. See PI. xvii. 



II. Table Showing Selected Results of the Oxidation of SulpJmr in Pyrite 

 and Marcasite by Solutions of EMnO^ at 22°. See PI. xviii. 



In plotting from these tables a vertical scale of one-half inch per one per 

 cent, of sulphur oxidized and a horizontal scale of three-quarters inch 

 per hour of oxidation have been employed. Wherever there was a drop 

 in the results the gap has been bridged over by the main curve, thus mak- 

 ing the curves as nearly as possible progressive, but the drop has been 

 plotted in fine dotted lines. On examining these curves the points as to 

 the relative rates of oxidation that have been mentioned are shown very 

 graphically, the curve of the marcasite oxidation rising in each case above 

 the corresponding one of pyrite, but both showing a similar form. Ot 

 these curves the y^^ normal solution cold and the 5 per cent, solution hot 



■ Obtained by omitting discordant results. 



