134 Decomposition of Iron Pyrites. 



property. It seems therefore liighl}' probable that the falling 

 usunder of the common pyrites arises from the electro-chemical 

 action of the electro-negative bi-snlphuret which is here and 

 there mixed with it in small particles." On comparing the fig- 

 ures quoted above, in the original experiment of Berzt lius, I find 

 by calculation that, according to his view, the mineral under 

 trial must have consisted of : 



Per Cent. Atomic Ratio. 



FeS-^ 86.04 j^ Eauivalentto ^^^ ^'^'^^ "^'^ ^^ 



FeS 13.96 f -B^qun aieni to ^g -^ gg ^ ^^g 20 



This is a relationship, however, which has never been report- 

 ed in the analysis of marcasite by Berzelius himself or any 

 other analyst, and is virtually contradicted by the results of 

 Kohler, already cited, and others, who have always obtained 

 the ratio 1 : 2. To account therefore for the apparent loss in 

 Berzelius' analysis, we must infer either the presence of a part 

 of the ferric sulphate in the residue insoluble in water, or a 

 remnant of impurity, perhaps a salt of baryta, in the precipi- 

 tate of ferric oxide, or, more probably, the previous escape of a 

 part of the sulphur from the decomposing mineral or from the 

 free sulphuric acid in the vitriol, in some form, it may be as 

 hydrogen sulphide. This gas might readily be generated 

 through the deoxidation of sulphuric acid by the organic matter 

 in the dust, introduced during the long exposure of two years 

 and a half. A further reference to this widely prevalent view is 

 made in connection with the chemical investigation described 

 beyond. 



7. Enclosure of clay in pyrites. Still another and more re- 

 cent view, worthy of consideration, is that of Messrs. A. Girard 

 and H. Morin,^ in their discussion of the pyrites of the French 

 deposits of commercial importance for the manufacture of sul- 

 phuric acid. These writers discriminate between three pyritous 

 varieties : 



a. Grayish yellow octahedral pyrite, of sp. gr. = 5, occurring 

 particularly in the volcanic formations and crystalline rocks ; 



' Ann. Ch. etPhys., (1876), Ser., 5, YII, 229. 



