recording apparatus for flame tests of explosives, also pressure gauges,
and a calorimeter, and, at the other end, is a gallery for testing
safety lamps.

The larger portion of the second floor is occupied by a gas-tight
training room for rescue work, and an audience chamber, from which
persons interested in such work may observe the methods of procedure. A
storage room for rescue apparatus and different models of safety lamps
is also on this floor.

The disruptive force of explosives is determined in three ways, namely,
by the ballistic pendulum, by the Bichel pressure gauge, and by Trauzl
lead blocks.

_Ballistic Pendulum._--The disruptive force of explosives, as tested by
the ballistic pendulum, is measured by the amount of oscillation. The
standard unit of comparison is a charge of ½ lb. of 40% nitro-glycerine
dynamite. The apparatus consists essentially of a 12-in. mortar (Fig. 3,
Plate VI), weighing 31,600 lb., and suspended as a pendulum from a beam
having knife-edges. A steel cannon is mounted on a truck set on a track
laid in line with the direction of the swing of the mortar. At the time
of firing the cannon may be placed 1/16-in. from the muzzle of the
mortar. The beam, from which the mortar is suspended, rests on concrete
walls, 51 by 120 in. at the base and 139 in. high. On top of each wall
is a 1-in. base-plate, 7 by 48 in., anchored to the wall by ⅝-in. bolts,
28 in. long. The knife-edges rest on bearing-plates placed on these
base-plates. The bearing-plates are provided with small grooves for the
purpose of keeping the knife-edges in oil and protected from the
weather. The knife-edges are each 6 in. long, 2-11/16 in. deep from
point to back, 2 in. wide at the back, and taper 50° with the