Number of large calories developed per kilogramme of explosive, for
comparison with 1,000 grammes of 40% dynamite, which develop, on an
average, 1,229 large calories.

Blasting Powder Separator.

The grains of black blasting powder are graded by a separator, similar
to those used in powder mills, but of reduced size. It consists of an
inclined wooden box, with slots on the sides to carry a series of
screens, and a vertical conduit at the end for carrying off the grains
as they are screened into separate small bins (Fig. 1, Plate X). At the
upper end of the screens is a small 12 by 16-in. hopper, with a sliding
brass apron to regulate the feed. The screens are shaken laterally by an
eccentric rod operated by hand. The top of the hopper is about 6½ ft.
above the floor. The box is 6 ft. 10 in. long, from tip to tip, and
inclines at an angle of 9 degrees.

After separation the grains fall through a vertical conduit, and thence
to the bins through zinc chutes, 1 by 2 in. in section. Care is taken to
have no steel or iron exposed to the powder.

The screens are held by light wooden frames which slip into the inclined
box from the upper end. In this way, any or all of the screens may be
used at once, thus separating all grades, or making only such
separations as are desired. The screens with the largest meshes are
diagonally-perforated zinc plates. Table 2 gives the number of holes per
square foot in zinc plates perforated with circular holes of the
diameters stated.