1894.] 



235 



[Brown. 



Action of a 5 Per Cent. Potassium Permanganate Solution 



AT 100^ C. 



This series was decidedly the most satisfactory of the experiments con- 

 ducted at 100° and, with the exception of the two-hour oxidations, in case 

 of each mineral shows a remarkably reguhir increase in the oxidation of 

 the sulphur. It illustrates, too, in the case of the pyrite, the effect of the 

 concentration of the solution due to evaporation. This causes a more 

 rapid rise in the results after three hours" action, and notably between 

 four and five hours. This rise is not so well seen from the table as from 

 the plot of the results given in PL xvii. Here this rising of the curve alter 

 three hours is very marked as contrasted with the curve of the marcabile 

 oxidations. 



Table Shoidng the Relative Oxidation of Sulphur in Pyrite and Marcasite 

 by a 5 Per Cent. Solution of KMn 0^ 100^. 



The graphic representation of the rate of oxidation of sulphur in these 

 two minerals is plotted from the following tables, the first of which shows 

 the average amounts of oxidation of sulphur compiled from the several 

 small tables already given. In this compilation I have omitted a few of 

 the results given in parentheses in the small tsibles as they are evidently 

 incorrect, and would vitiate the averages. On the other hand, I have sim- 

 ply retained the parentheses of the small tables in certain cases where but 

 one result was obtained. The second table, also compiled from the sev- 

 eral small tables, shows for the experiments at ordinary temperature the 

 result of selecting, wherever possible, such individual determinations as 

 show a progressive increase in the oxidation. In this way more regular 

 series of results are obtained. Inasmuch as the variations are so marked, 

 this method of selecting results seems justified, at least for obtaining a com- 

 parison of the relative rates of oxidation of the sulphur in the two min- 

 erals. The results of Table i are plotted in PI. xvii, and those of Table ii in 

 PI. xviii. 



