Blown.] ■'-^*-' [May IS, 



perature of the air for twelve hours. The residue was extracted with 

 dilute H.^SO^, which removed the iron rendered soluble (bromide), and 

 the iron was then determined in this solution. The percentage of iron 

 that had dissolved varied from 3.43 to 15.20 per cent.,' although all sam- 

 ples tested are described as pyrite. He also tried the action of bromine 

 in aqueous solution, but the reaction was loo rapid to give any compara- 

 tive results. 



Much more important are the results obtained in the oxidation of these 

 minerals by the electric current as conducted by Prof. Edgar F. Smith,* 

 and it was the remarkable results that were then obtained that induced 

 me to continue the study of the comparative reactions of these two min- 

 erals Smith found that a current which would completely oxidize the 

 sulphur in marcasite in a given time would oxidize less than half of the 

 sulphur in pyrite in the same time. This remaining sulphur was held 

 very tenaciously, though the mineral was subjected to more powerful cur- 

 rents and longer continued action than in the case of marcasite or pyrrho- 

 tile. Finally, by adding an equal quantity of CuO, and using a more 

 powerful current, all ot the contained sulphur was oxidized. Previous 

 to the addition of CuO but 21 or 22 per cent of the sulphur was oxidized. 

 In concluding the article above referred to the author questions whether 

 the crystalline form alone can make this difference in the action of the 

 two minerals when under the influence of the current. 



The two samples of pyrite and marcasite that I selected for the follow- 

 ing study were chosen after considerable examination of material as being 

 typical of the two forms of FeS.^. The pyrite was from the hematite 

 mines of Elba. It is exceptionally pure and free from decomposition or 

 tarnish. Before deciding on it finally pieces were gnmnd and polished 

 and then examined under the microscope with powers ranging from 50 to 

 200 diameters, in order to see if it contained any enclosures or varied in 

 texture. It was perfectly homogeneous and showed no enclosures. It 

 took a high polish. The crystals showed the combination of octahedron 

 and pentagonal dodecahedron O + ?§-. Some of the crystals were coated 

 in places with scales of hematite, but this was all carefully removed in 

 breaking up material for experiment. The color was bright brass-yellow, 

 the specific gravity was determined as 5.179. The marcasite was from the 

 zinc mines of the Subcarboniferous of Joplin, Jasper county. Mo., finely 

 crystallized in polysynthetic twinnings. The freshly broken crystals show 

 a greenish yellow color, almost white, but they tarnish readily with bluish 

 or brownish colors. No gangue was present, everytliing dissolving com- 

 pletely in nitric acid. This marcasite was examined with the microscope in 

 the same way as the pyrite ; it did not take such a high polish on account of 

 a fibrous structure, but no foreign matter was found with a power of 200 

 diameters. Its color was uniform throughout, showing that no pyrite 

 was present. The specific gravity as determined was 4.844. 



In preparing material for experiment only suflicient was ground forim- 



*Jf>ttr. Franklin Inst., Vol. cxxx, pp. 152-251. 



