372 



Decomposition of Iron Pyrites. 



analyses of nickel iferous varieties are omitted from considera- 

 tion, as well as those of material whose density has been evi- 

 dently decreased by the presence of light impurities, such as 

 limonite (So. 26) and quartz (No. 30), and also the abnormal 

 figures of the analyses of Hatchett, Middleton, etc. (Nos. 24, 

 25, 31 and 32). Some of the determinations of specific gravity, 

 presented in the preceding table, were unaccompanied by analy- 

 ses (Nos. 6, 14 and 27). The sixteen remaining varieties have 

 been arranged in the order of decreasing density, and divided, 

 as nearly as possible, into three groups as they stand. 



Composition. | 



No. of Variety. 



8p. Gr. 



Fe. 



8. 



Formula. 



3 



4.642 



60.75 



39.25 





4 



4.642 



60.41 



39.59 





5 



4.640 



60.76 



39.24 





7 



4-627 



61.44 



38.56 





8 



4.627 



59.93 



40.07 





9 



4.623 



60.26 



39.74 





{Average of group.) 



(4.633) 



(60.59) 



(39.41) 



Fe 7 S* 



10 



4.622 



60.97 



39.03 





11 



4.622 



61.18 



38.82 





12 



4.622 



60.81 



39.19 





16 



4.584 



60.75 



39.25 





17 



4.583 



59.82 



40.18 





(Average of group.) 



(4.607) 



(60.71) 



(39.29) 



Fe 8 8? 



18 



4.580 



60.83 



39.17 





20 



4.564 



61.30 



38.70 





21 



4.546 



61.15 



38.85 





23 



4.540 



61.16 



38.84 





29 



4.494 



60.76 



39.24 





(Average of group.) 



(4.545) 



(61.04) 



(38.96) 



Fe 9 S 10 



In his discussion of the constitution of pyrrhotite, Ram- 

 melsberg states the opinion : "the density (volumgewicht) 

 leads to no conclusion, since the lightest show the same compo- 

 sition as the heaviest, to wit, about Fe 9 S 10 ." Now, in fact, most 

 of the analyses of pyrrhotite (as well as of the other iron pyrites) 

 were partial and therefore imperfect, consisting only of a deter- 

 mination of the amount of iron, that of sulphur having been 

 estimated from the difference, by deduction from 100. But if 

 we can trust the accuracy of the figures in this table, the signifi- 

 cant fact appears to be brought out that an increase in the 

 amount of iron and a corresponding decrease in that of sulphur 

 are accompanied by a decrease of density. This at least sug- 

 gests a confirmation of the view that we may have in this min- 



