explosives and a shallower, slowly rising curve for explosives of slow
detonation. When the gases cool, the curve merges into a straight line,
which indicates the pressures of the cooled gases on the sides of the
chamber.

[Illustration: PLATE VIII.

Fig. 1.--Explosives Calorimeter.

Fig. 2.--Building No. 17, and Flame-Test Apparatus.

Fig. 3.--Small Lead Block Test.]

Since the ratio of the volume of the cylinder to the volume of the
charge may be computed, the pressure of the confined charge may also be
found, and this pressure often exceeds 100,000 lb. per sq. in. The
cooling effect of the inner surface on the gaseous products of
combustion, a vital point in computations of the disruptive force of
explosives by this method, is determined by comparing the pressures
obtained in the original cylinder with those in a second cylinder of
larger capacity, into which has been inserted one or more steel
cylinders to increase the superficial area while keeping the volume
equal to that of the first cylinders. By comparing results, a curve may
be plotted, which will determine the actual pressures developed, with
the surface-cooling effect eliminated.

_Trauzl Lead Blocks._--The lead-block test is the method adopted by the
Fifth International Congress of Applied Chemistry as the standard for
measuring the disruptive force of explosives. The unit by this test is
defined to be the force required to enlarge the bore-hole in the block