13? 



more than simple modifications of one and the same power, origi- 

 nally belonging to matter ; but he maintains, at the same time, that 

 these modifications certainly exert as much force, at the time of their 

 operation, as could be exerted by attractive forces that are really dif- 

 ferent. 



In the third part, which treats of the different kinds of sulphuret 

 of copper, we are first apprised of the importance of this inquiry, by 

 the observation, that, on comparing the different characters of this 

 substance with those of the triple sulphuret described in the first part 

 of this paper, we shall find that the antimony and the lead, which 

 have been generally considered as constituent parts of the last-men- 

 tioned ore, are, in fact, nothing more than accidental ingredients, 

 introduced merely by the attraction of aggregation. 



In the sequel of the paper, the author introduces an ample stock 

 of observations and analyses respecting various cupro-sulphurets, 

 which have been hitherto very imperfectly examined. And first he 

 treats of the gray tetrahedral sulphuret of copper, which is found to 

 consist of copper, iron, and sulphur, in different proportions ; the 

 gray copper ore, called Fahlerz by the Germans, being of the same 

 composition. The yellow copper ore, or Kupferkies of the Germans, 

 appears to be double sulphuret of copper and iron, but constituting 

 a species distinct from the gray sulphuret of the same tetrahedral 

 form. Among these, there is one in particular which has not yet 

 been described as belonging to this ore ; namely, the dodecahedron 

 with rhombic planes, which has hitherto been found only in Corn- 

 wall, and there only in small quantities, though in crystals of con- 

 siderable size. It is also shown at length wherein most of the cha- 

 racters of the tetrahedral yellow cupro-martial sulphuret differ from 

 those of the octahedral sulphuret of iron. 



The following question is next proposed, and strongly recommended 

 to the future investigation of mineralogists. As the true sulphuret 

 of copper and the fahlerz are of a blackish gray colour, how comes it 

 that the kind of cupro-martial sulphuret, commonly called pyritical 

 copper, has always that brilliant yellow colour which particularly 

 characterizes it, and which is the principal cause that leads many 

 mineralogists to consider it as being nothing more than a martial 

 pyrites mixed with copper ? The solution of this difficulty, we are 

 told, will materially contribute to ascertain the external characters of 

 this kind of sulphurets. 



The cupro-martial sulphuret, called by Werner Buntkupfererz, is 

 a new species of this ore, which crystallizes in forms that are peculiar 

 to it, and not at all analogous to those of the other cupro-martial 

 sulphuret. The ingredients, which are solely copper, iron, and sul- 

 phur, differ considerably in their proportions in different specimens. 



The author desires that what he has here said may be considered 

 merely as a cursory account of some of the sulphurets of copper,, from 

 which, however, he thinks it may be inferred, that there exists a great 

 number of species of this substance which have not yet been de- 



