IRON—MARTIAL PYRITES—VITRIOL.
488
air, and of humidity at the fame time, undergo a change, by which
the sulphur becomes sulphuric acid, and we get a vitriol, or sulphat
of iron, in place of the pyrites, or compound of iron and sulphur.
Humidity alone is not fufficient. The pyrites has not the power of
decompounding water. Cramer fays he observed immense quantities
of pyrites all along the Englifh ſhores, especially about Harwich,
which naturally lie in a bed at the depth of some feet below the sur
face of the sand. As long as they lie there, though they are constantly
wet with ſea water, they continue entire and quite insipid, but when
thrown up to the air by the waves, they are crumbled down, and
converted almost entirely into a heap of little crystals, in a fortnight.
This is indeed the case every where, for the pyrites is always exposed
to abundance of humidity in the bowels of the earth, but nevertheless
retains its form until it is dug up and exposed.
This change, which the pyrites of iron is liable to undergo, is called
vitriolization, —it is ſaid to vitriolize.
It is proper to remark, however, that only particular kinds of py
rites are liable to it, not every kind. Some kinds, fuchas the cubi
cal pyrites, common in slate, and some others, withstand the action of
air and humidity a long time without suffering a change, or if they are
changed, it is very flowly, and only into a hard rust at their surface,
but without affording vitriol.
The cause of this difference among the varieties of pyrites has not
been discovered. I fuspect that it depends upon the proportion of
the ſulphur to the iron, and that thoſe which contain moſt sulphur are
moſt liable to vitriolization.
Process for Vitriol from lron Pyrites.
The account which I have given you of the chemical procedure
will naturally direct you to the proper methods of accelerating the
operation. I have only to remark, that some kinds of pyrites require
a preparation, by roasting in a heap with a small quantity of fuel. This
is found to dispose the harder pyrites to a more rapid decomposition;