that the latter shall have a little play. By means of a hammer, m, a
smart blow is given the valve i, and this detonates the priming, and
causes an explosion of the charge. The gases make their exit through the
pyramid, h, and lift the valve and press it against the plug, so that
their escape is effectually prevented. In fact, the explosion takes
place without noise. A slight whistling, only, indicates that the
capsule has not missed fire, and that the apparatus may be immediately
opened, the gases having condensed in the interior. It is well, however,
to place the closed apparatus in water, in order that the residua that
have entered the threads of the screw may become detached, and that the
apparatus may be opened easily. Although there is no danger in standing
alongside the apparatus, it is much better to spring the hammer by means
of a cord of a certain length, since the valve and especially the
pyramid gradually burn and may be thrown out. With some kinds of powder
the pyramid rapidly melts, and must be frequently replaced.

[Illustration: APPARATUS FOR MEASURING THE FORCE OF EXPLOSIVES.]

The two cones of lead obtained are then measured to 0.004 of an inch by
means of a gauge (Fig. 3).

The inventor has made numerous experiments with his apparatus, and
thinks it permits of determining the total force developed by powder
very perfectly.

* * * * *