on certain stony and metalline Substances, &c. 291 
pyrites of the stone from Benares, may therefore be considered 
nearly thus : Grains. 
Sulphur - 2 
Iron - - - - - 1 o-- 
2 
Since 15 grains of the oxide represent about that quan- 
tity of iron, 
Nickel, nearly - - ~ 1 
Extraneous earthy matter 2 
*5f- 
It is observable that, notwithstanding the loss appears to be 
only half a grain, it was probably more, because the sulphur 
could not be reduced to the same state of dryness in which it 
existed when in combination with the iron ; not to say that it 
was, in a small degree, volatilized with the hydrogen gas dis- 
engaged during the solution. 
The weight of nickel is a mere estimation. We are not yet 
sufficiently acquainted with that metal to speak of it with 
accuracy, except as to its presence. Upon the whole, however, 
it may be concluded, that these pyrites are of a very particular 
nature ; for, although Henkel has observed that sulphur may 
be separated from pyrites by muriatic acid, it is by no means 
the usual habitude of pyrites to be of such easy decomposition. 
The other shining particles immediately seen, when the 
internal structure of the stone is exposed, are the malleable 
iron. Before I state the examination of this iron, I must remark, 
that preliminary experiments having shewn me it contained 
nickel, I treated several kinds of the most pure irons I could 
obtain, with nitric acid; and precipitated the oxide from the 
metallic salt by ammonia. The quantity of oxide I obtained 
from 100 grains of iron, was from 144 to 146. I may consequently 
