triple Sulphuret , of Lead, Antimony, and Copper, &c. 59 
have already said, appears to me by no means easy. Is it pos- 
sible that the iron, which Mr. Proust, in his Memoir upon 
metallic Sulphurets, has shown to be in a metallic state in the 
sulphuret of iron, is also in a metallic state in the yellow double 
sulphuret, and is, on the contrary, in the state of oxide in the 
gray double sulphuret? Or, can the property of emitting a 
beautiful phosphorescent fiery light, when thrown upon a heated 
iron, (which property is common both to the yellow double 
sulphuret, and to the martial pyrites,) have any connection with 
the cause upon which the colour depends ? It is true that Mr. 
Proust, in the memoir already referred to, says that the sul- 
phuret of copper, when in its state of greatest purity, is of a 
deep blue colour, with a coppery appearance: and he states 
this colour to be one of the characters by which that substance 
may be distinguished. This observation may perhaps be true, 
with respect to the artificial sulphuret of copper, for I am not 
acquainted with that substance: but it would certainly lead astray 
any naturalist who should attempt to use it as a guide to dis- 
tinguish the natural sulphuret of copper. The true colour of the 
latter substance, when in its most pure state, is a very dark 
gray. In that state, it assumes a peculiar crystalline form, and, 
when cut with a knife, exhibits a metallic lustre, as is the case 
with sulphuret of silver. 
A portion of iron sometimes combines with the sulphuret of 
copper, and produces a new kind of double sulphuret, which really 
exhibits the colours mentioned by Mr. Proust, and particu- 
larly the reddish colour of copper, or of nickel : it is the Bunt - 
kupfererz of Werner. This new kind of double sulphuret also 
crystallizes, and in forms which are peculiar to it, and which 
are not at all analogous to those of the other double sul- 
I 2 
