Brown.] 



230 



[May 18, 



duced with metallic zinc and titrated with permanganate, but no iron was 

 found in the solution. 



The two minerals did not present the same appearance when acted on 

 bv the oxidant. Pyrite retained its color and seemed as pulverulent as 

 when the permanganate was added, but marcasite immediately on the 

 addition of the reagent became coated with manganese dioxide, took on a 

 brownish color, and showed a tendency to cake together and slick to the 

 sides of the bottle, so that it was with difficulty dislodged. This tendency 

 of the marcasite was more marked with stronger solutions of the perman- 

 ganate and was doubtless the cause of much of the irregularity that will 

 1)6 noticed in the results. The reason for this difference in action of the 

 reagent on the two minerals will be discussed later on. 



The percentages of sulphur oxidized in the two minerals by this method 

 are shown in the following table, where all results that were obtained are 

 recorded. The figures show the percentages of sulphur oxidized, calcu- 

 lated on the basis of FeS.^ equal to one hundred per cent. It will be noted 

 thatihe four-hour oxidation of marcasite shows a result that is less than 

 tlie two-hour. This was due to caking of the mineral against the walls of 

 the bottle, which prevented much of it from coming in contact with the 

 solution. On the whole, this series was about the most satisfactory of the 

 cold experiments with KMnO^, the action of this dilute solution being 

 less rapid and hence more even than that of the more concentrated solu- 

 tions ; naturally the action ceases with a certain dilution, and hence the 

 four- and five-hour oxidations of pyrite are about equal. 



Tnhle Showing the Relative Oxidation of SulpJiur in Pyrite and Marcasite 

 hy a T^o N. Solution of KMnO^ at 22°. 



The curves formed by plotting these results oa rectangular cc ordinates 

 are shown in Pis. xvii and xviii. The}' are marked 22° Mj for the marcasite 

 and 22° Pi for the pyrite. 



Action of 1 Per Cent. Potassium Permanganate Solution at 

 Ordinary Temperature. 



This and also the two following series were performed as described 

 under ^hvi normal solution above. At least two experiments were 

 tried with each mineral in this and the two following cold oxidations, 

 and whenever a result was notably higher or lower than its dupli- 



