Fig. 3.—Ballistic Pendulum.
The cannon consists of two parts, a jacket and a liner. The jacket is 36 in. long, has an external diameter of 24 in., and internal diameters of 9½ and 7½ in. It is made of the best cast steel or of forged steel.
The liner is 36½ in. long, with a 1-in. shoulder, 7¾ in. from the
back, changing the diameter from 9½ to 7½ in. The bore is smooth, being 2¼ in. in diameter and 21½ in. long. The cannon rests on a 4-wheel truck, to which it is well braced by straps and rods. A track of 30-in. gauge extends about 9 ft. from the muzzle of the mortar to the bumper for the cannon.
The shot is fired by an electric firing battery, from the first floor of Building No. 17, about 10 yd. away. To insure the safety of the operator and the charger, the man who loads the cannon carries a safety plug without which the charge cannot be exploded. The wires for connecting to the fuse after charging are placed conveniently, and the safety plug is then inserted in a box at the end of the west wall. The completion of the firing battery by the switch at the firing place is indicated by the flashing of a red light, after which all that is necessary to set off the charge is to press a button on the battery. An automatic recording device at the back of the mortar records the length of swing which, by a vernier, may be read to 1/200 in.
Bichel Pressure Gauges.—Pressure gauges are constructed for the purpose of determining the unit disruptive force of explosives detonating at different rates of velocity, by measuring pressures developed in an enclosed space from which the generated gases cannot escape. The apparatus consists of a stout steel cylinder, which may be made absolutely air-tight; an air-pump and proper connections for exhausting the air in the cylinder to a pressure equivalent to 10 mm. of mercury; an insulated plug for providing the means of igniting the charge; a valve by which the gaseous products of combustion may be removed for subsequent analysis; and an indicator drum (Fig. 1, [Plate VII]) with proper connections for driving it at a determinable speed.
Fig. 1.—Bichel Pressure Gauges.