284 Mr David Forbes on Chemical Ejcamination of 



According to this classification, we should have only two 

 distinct minerals, namely, — 



1. The disulphuret of copper (vitreous copper ore, or 

 glance copper), under which we at the same time include the 

 two minerals analyzed by Klaproth, and apparently regarded 

 by him, though erroneously, as purple copper ore. For the 

 sake of comparison, we not only repeat these two analyses, 

 but also add two analyses of the ordinary vitreous copper 

 ore, in one of which it will be seen that iron is present in 

 greater quantity than usually ascribed to accidental impurity, 

 and apparently replaces some part of the copper. 



Klaproth's Analyses corrected. Vitreous Copper Ore. 



I. II. Klaproth. Thomson. 



Sulphur, . 20-00 19-79 18-50 20-62 



Copper, . . 61-06 72-39 78-50 77-16 



Iron, . . . 18-95 7*82 2'25 1-45 



Silica, . . -75 



100-00 100-00 99-00 99-23 



The formula Cug S will give the pure disulphuret to be 

 composed of — 



Sulphur, .... 20-27 

 Copper, . . . . 79-73 



100-00 



which closely agrees with the above results. 



2. The purple copper ore, considered as a compound of 

 the disulphuret with the protosulphuret of copper in varying 

 proportions, and with iron replacing more or less of the cop- 

 per in the disulphuret. The analyses previously given can be 

 represented by the following subordinate formulae : — 



(a) 2 Cug S + Cu S, as exemplified in the mineral analyzed 

 by Philipps from Killarney in Ireland. This formula gives 

 sulphur 23-38, copper (with iron) 76-62 = 100. 



(b) Formula Cug S 4- Cu S, as in the mineral here noticed, 

 as well as those analyzed by Bodemann, Hisinger, and 

 Plattner, giving sulphur 25-31, copper (with iron) 74-69 = 

 100. 



