Specimens of Purple Copper Ore and Copper Pyrites. 285 



(c) Formula Cug S + 2 Cu S, represented by the crystalline 

 variety analyzed by Plattner. Likewise I must regard the 

 mineral called Digenite, discovered by Breithaupt, and ana- 

 lyzed by Plattner, as belonging to this class, being the pure 

 sulphuret, without replacement of iron. 



The per-centage results are as follow : — 



Formula Cu , S + 2 Cu S. Digenite.* 

 Sulphur, . 27*60 29*0 



Copper, . 72-40 71-0 



100-00 1000 



We have thus included the whole of those minerals under 

 a general formula, which is apparently simpler than that 

 we should give each one of them, so similar as they are in 

 physical properties, a distinct and varying formula, differing 

 so much from each other, that we could never admit of their 

 being associated together in any general chemical series ; 

 whereas by adopting the above view, w^e have at once both 

 a systematic classification, and some reasons for the differ- 

 ent results obtained by the several analysts. It must, how- 

 ever, be left to other chemists and mineralogists to give a 

 more decided opinion on, and to examine more carefully into, 

 the correctness of this hypothesis. 



II. Yellow Copper Pyrites. — The specimen massive and 

 apparently free from all admixture of earthy matter. Me- 

 tallic lustre, fine yellow colour, not easily tarnished. Streak 

 greenish-grey, and when powdered gave a dark green pow- 

 der. Cleavage indistinct. Hardness about 3*5 ; and specific 

 gravity, taken at 60° Fahrenheit, was 4-185. 



The method of analysis employed was nearly the same as 

 described under the preceding mineral, with the exception 

 that the solution was effected by heating it with nitric acid 

 and chlorate of potash, until the sulphur separated of a clear 

 yellow colour. A fresh portion of the mineral was employed 

 to determine the bases. The quantities employed and found 

 were as follow : — 



♦ The analysis of Digenite here given is taken from " Naumann's Elemente 

 der Mineralogie," p. 402, as I have not seen the original results by Plattner. 



