Pressure-gauge

Called also pre ure-plug . An apparatus invented by Gen. Rodman for measuring the pre ure exerted by the gases of exploded powder. It consists e entially of a steel plunger, on the head of which the pre ure is exerted. The other end of the plunger is widened out into two cutting edges which meet at an obtuse angle. This point rests on a disk of copper, into which the cutter is driven by the pre ure. The pre ure is deduced from the length of the cut. Two forms of the instrument are used,—one is placed in a hole bored through the side of the gun. The other is complete in itself and is placed at the bottom of the cartridge-bag. Lieut. Metcalfe’s (U. S. Ordnance Corps) modification of the pre ure-gauge has a cutter with a helicoidal edge. To measure the cut he uses a circular scale with a hole in the centre (in which the inducted copper is placed), and a radial arm to show the extent of the spiral cut. The English modification of Rodman’s instrument is called the crusher-gauge ,—a short cylinder of copper is substituted for the disk,—the reduction in its length gives a measure of the pre ure. The crusher-gauge is frequently attached to the base of the shot. A similar modification is used to test the power of the high explosives, such as dynamite, dualin, etc. A lead cylinder is crushed in this case. A very small charge is used. The reaction is obtained by placing a heavy cylindrical shot over the charge, which rests directly in a cavity on the top of the plunger.