arc of a circle; the buckets grazed the
surface of the bottom and sides of this kettle, the bottom of the latter
being immersed in a current of cold water. The hot filtered solution of
the crude saltpetre was received into this kettle, and thus kept into a
state of rapid agitation, the effect being to produce a wet mass of
minute crystals, which, as fast as formed, were taken up by the sharp
edged buckets, and lifted sufficiently high to pour into a receiving
vat; this permitted the liquid part to flow back into the kettle. By
this means in a short time the entire mass of fine deposited crystals
from the rapidly cooled liquid, were removed to the vat. When the
operation was completed the remaining liquid in the kettle was by the
revolutions of the bronze wheel, discharged into one of the eight
capacious cisterns below the floor; there were two of these machines
employed.

The facility for work which this apparatus, with the other mechanical
appliances afforded, enabled the refinery to carry the purification of
the saltpetre beyond that of the most celebrated powder factories.

Adjoining this part of the Works was the Sulphur Refinery, where this
material was prepared from the crude stock, and made ready for the
incorporating process. About one hundred and thirty tons of very impure
sulphur had been received from Louisiana, for the use of the Powder
Works; it had been purchased before the war by the planters for use in
the making of sugar, and was bought up by the Confederate officers. The
best quality of gunpowder has its sulphur chemically pure, which could
be demonstrated by showing no trace of acid when powdered and boiled in
water, and should entirely evaporate on a piece of glass when heated,
leaving no stain. This can only be accomplished practically by
distillation. The crude article was melted and poured into upright,
thick wooden boxes five feet high and ten inches square at the bottom,
tapering upwards; when cold the earthy matters would be found in the
lower portion by subsidence, leaving about three feet apparently pure.
This was broken off and placed into two kettles of suitable form and
dimensions, having furnaces; the tops of these kettles were connected by
a bent iron pipe to an enlarged portion, which was surrounded with
water. On the application of heat the sulphur vaporized, and passing
over through the pipe was condensed in the cooled portion, whence it
trickled in a thick stream into a receiving v