SVJ.PHUnr.T OF LEAD, copper, a.vo antimony. 333 



lively colours, till at last it loses great part of the copper it 

 contained; and which very frequently in this case, com- 

 bining with carbonic acid, passes to the state of green cop- 

 per, leaving a residuum of oxide of iron, which however is 

 still sometimes pretty rich in copper, and is then known by 

 the name of hepatic copper ore. 



Care must be taken not to confound this double sul- This not to b« 

 phuret of copper and iron, as is frequently done, with the V^ "" ^ 

 martial pyrites that contains copper intermingled with its pyrites in 

 substance, commonly in small quantity, though it is some- ™ ijuermixed! 

 times pretty rich in this metal. From this the double sul- 

 phuret is totally different. The form of the martial pyrites 

 containing copper is either a cube, and this commonly 

 striated, or a regular octaedron. The martial pyrites is 

 likewise much harder than the yellow sulphuret of copper 

 and iron, and it is heavier, its mean specific gravity being 

 4-944*. It must appear very strange, that this sulphuret, 

 hiving great analogy in its component parts, as well as in 

 its form, with the gray sulphuret, or fahlertz, should have 

 a colour so very different from it, as well as from all the 

 other sulphurets of copper. Endeavouring to account for Cause of the 

 this, I have always been led to think, that this difference of ™^ ace of 

 colour might arise from the iron's being in the perfectly 

 metallic state in the yellow sulphuret of copper and iron, 

 as it is in the martial pyrites, while in the gray sulphuret it 

 is oxided. This opinion however I only mention as a great 

 probability f. 



In 



* This specific gravity is a mean of those taken from crystals all 

 of different forms. Authors give for it from 4*100 to 4-749. Cer- 

 tainly however they have not taken it in the same manner from 

 crystals, but from amorphous masses ; or' at least it must have beeu 

 from very impure crystals, otherwise they would not have varied 

 from 41 to more than 4-7; and it would even have been found 

 superior to this maximum. 



f I have observed with the greatest satisfaction, that the opinion I 

 had long embraced respecting the cause of the difference of colour 

 between the yellow sulphuret of copper andiron and the gray, and 

 which was inserted in my first paper on endellion presented to the 

 Koyal Society, has been verified by the analyses made by Mr. 

 Gueniveau of two varieties of yellow sulphuret of copper and iron 



from 



