tion by the
action of steam, the hot solution of saltpetre would speedily penetrate
the minute pores of the charcoal, and thus the desired end would be
rapidly attained.

Accordingly, the following process was devised: The moistened sixty
pounds charges, roughly mixed and moistened with water, were introduced
into horizontal cylinders of sheet copper thirty inches long by eighteen
inches in diameter. These cylinders revolved slowly on a common axis,
consisting of a heavy brass tube three inches in diameter, perforated
with holes. High pressure steam was introduced through the tube raising
the temperature to the boiling point while the water produced by
condensation, added to that originally used to moisten the materials,
reduced them to a semi-liquid slush, which was run out of the cylinders
after about eight minutes rotation. On cooling, this mud became a damp
solid cake, the saltpetre which in the state of boiling hot saturated
solution had entered the minutest pores of the charcoal, now
crystallizing. The cake as produced was transferred to the incorporating
mills, and under the five ton rollers was in an hour brought to the
condition of finished mill cake, ready to be cooled and granulated,
while without the steaming process, four hours incorporation in the
mills had previously been necessary to produce powder of the same
first-class character. The capacity of the work of the mills was thus
practically quadrupled, the thorough saturation of the charcoal with
saltpetre being accomplished by the steaming, while it remained for the
rollers merely to complete the incorporation of the whole mass and give
the required density to the mill cake.

The Incorporating Mills, twelve in number, extended along the canal
beyond the Refinery building and further back from its bank, having the
Laboratory between the two; they were two hundred and ninety-six feet
long. This separation was for safety, as they worked explosive material.
The walls were massive, being four to ten feet thick, the horizontal
section of each being that of a huge mortar of seventeen feet wide by
twenty-four feet long; the height of the walls was twenty-eight feet;
they faced alternately in opposite directions, so that an explosion of
one would not be communicated to those adjoining.

The fronts were constructed of light wood and glass, and the roofs of
sheet zinc, so that but slight resistance would be offered, upwards and
outwards, to the explosive force.