542 Kraus and Goldsberry — Chemical Composition of 



then recognized formulas for bornite. Doelter, therefore, con- 

 cluded that bornite could be considered as an isomorphous 

 mixture of Cu 2 S, CnS, and Fe„S 3 , in varying proportions. 



Rammelsberg revised his earlier ideas in 1895 and gave as 

 the general formula jp Cu^S.^CuS.r FeS, in which the relation- 

 ship of the metals to the sulphur could vary greatly. Ram- 

 melsberg further considered the composition of crystallized 

 bornite as Cu 2 S.CuS.FeS = Cu 3 FeS 3 , but to some varieties he 

 assigned the formula Cu ]0 Fe„S e . 



Gfroth* in 1898 interpreted bornite as Cu 3 FeS 3 , and placed 

 it in a group with chalcopyrite, CuFeS„, and barnhardtite, 

 Cu 4 Fe 3 S 5 . These three minerals were thought to be deriva- 

 tives of Fe(SH) 3 . More recently Harrington,f in 1903, ana- 

 lyzed some crystallized bornite from Bristol, Connecticut, 

 obtained from the Brush Collection of minerals of Yale Uni- 

 versity, and concluded from the results of the analysis of this 

 and other material, and also from a study of previous analyses, 

 that the chemical composition of bornite is best indicated by 

 the formula Cu 10 Fe„S 8 or Cu 5 FeS 4 . 



Chemical Investigations. 



Inasmuch as crystallized bornite is exceptionally scarce it 

 was thought advisable to use some of the material for an 

 analysis, and accordingly all of specimen 4 and a portion of 

 specimen 1 were sacrificed for this purpose. Specimen 4 con- 

 sisted of an aggregate of cubical crystals. These were covered 

 with a dark-colored coating which was thoroughly removed 

 before the material was crushed for the analysis. The material 

 from specimen 1 was the lower portion of the crystal repre- 

 sented by fig. 1, and was entirely free from any superficial coat- 

 ing. The material was, as far as could be determined by the 

 ordinary methods, homogeneous in every respect. This was 

 later substantiated by a careful metallographic study of speci- 

 men 1. 



Sulphur was determined by oxidation to the sulphate with 

 sodium peroxide and precipitation as BaS0 4 . The copper was 

 determined electrolytically, and the iron volumetrically by 

 oxidation with potassium permanganate. The specific gravity 

 of specimen 1 was determined as 5 - 086 at ordinary tempera- 

 tures. The results of the analysis are as follows : 



1 II Average Ratios 



Copper 



Iron 



Sulphur . _ . 



65-42$ 



9-74 

 24-79 



65-91$ 



9-67 

 24-51 



65-665$ 



9-705 

 24-650 



100-020 



1-03296 

 0-17377 

 0-76863 



12-000 

 2-019 



8-927 



* Tabellarische Uebersicht der Mineralien, 4th edition, 29. 

 f This Journal, xvi, 151-154, 1903. 



