triple Sulphuret, of Lead, Antimony, and Copper, &c. 57 
parts that are smooth, and sometimes partially conchoid; which 
appearances are never observed in the octaedral sulphuret of 
iron. The hardness of this double sulphuret is also less con- 
siderable. The octaedral sulphuret of iron scratches it with 
great ease ; and, if we endeavour to obtain sparks from it, by 
means of a piece of steel, it is with great difficulty that any can 
be procured : it is also more brittle. If grossly powdered, and 
thrown upon an iron heated to redness, although it then emits 
a strong smell of sulphureous acid, w T e do not perceive that in- 
flammation of the uncombined sulphur which, as I have already 
said, takes place when the octaedral sulphuret of iron is treated 
in the same manner; yet this last-mentioned kind of sulphuret, 
and that in striated cubes, are those which contain the smallest 
quantity of superabundant or uncombined sulphur. The powder 
of the yellow double sulphuret, however, when thrown upon the 
hot iron, emits a fiery red light, similar to that which proceeds from 
the sulphuret of iron ; indeed its light is still more vivid. Lastly, 
its specific gravity is less considerable ; that which I obtained 
from a trial of several crystals, of a perfectly determinate form, 
was always between 4000 and 4100; the mean being 4058. 
Whereas, the specific gravity of the octaedral sulphuret, taken 
in similar circumstances, was between 4900 and 5000; the 
mean being 4944. 
But the yellow double sulphuret, notwithstanding it exhi- 
bits, or at least seems to exhibit, the same primitive form as 
the gray tetraedral sulphuret, (although it is far from admit- 
ting its various modifications,) seems to be by no means of 
the same nature with it, and ought, in my opinion, to be con- 
sidered as forming' a species which, though analogous to the 
other, is really different from it. The colour (a character of 
mdccciv. I 
