328 SULPHURS! OS LBlD, COPPER, AND ANTIMON*. 



which it would have been of great importance to make 

 known. 

 Exainfcation of The attention which the different sulphurets of copper 

 appear to me to deserve, as opinions respecting them are 

 not yet settled, induces me to add to what I have said on 

 the fahlertz, or tetraedral sulphuret of copper and iron, 

 the following reflections. Part of them have already ap- 

 peared in my first paper on endellion ; but the observations 

 which I have subsequently had an opportunity of making 

 on the sulphuret of copper enable me to present these re- 

 flections to the Royal Society again on a larger scale, and 

 in a manner better adapted to illustrate this interesting sub. 

 ject, on which so much uncertainty prevails. 

 Extraneous The substances foreign to fahlertz, or tetraedral gray 



substances mix- CO p per -which observation has hitherto shown to be inter- 

 posed in it, are silver, lead, antimony, and arsenic ; and 

 very frequently these substances appear to be sulphuretted, 

 as well as the copper. An analysis by Klaproth of a va- 

 riety from Kapnick, in Hungary, has even indicated 0*06 of 

 zinc; and another of a variety from Poratsh, in Upper Hun- 

 gary, 0*0625 of mercury. These substances, several of 

 which are sometimes found in the variety, that possesses the 

 property of crystallizing, are no obstacle to crystallization : 

 but there are many other varieties, that appear to be desti- 

 tute of this property. In spite of all the researehes I have 

 been able to make on this subject, I cannot establish in a 

 satisfactory manner the characters, that might serve to make 

 them known : in general the gray colour of the crystailizable 

 variety is I think less deep, and its lustre more brilliant, but 

 to this there are many exceptions. 

 All the gray sul- The fahlertz is not the only sulphuret of copper, that is 

 per [fable tofo- subject to this interposition of foreign substances ; it is the 

 leign mixture, same with all the gray sulphurets of this metal. The various 

 mixtures they contain has even occasioned different names to 

 be given them, and different opinions to be entertained re- 

 specting their nature. From the silver, which some of its 

 varieties contain, fahlertz had long the name of gray silver 

 ore. Afterward, when it was found, that a great number 

 of other varieties were totally devoid of silver, it was called 

 gray copper ore. An analysis, which Klaproth made of a 



variety 



