AIR-GUN. A machine in which highly-compressed air is substituted for gunpowder tp expel the ball, which will be projected forward with greater or less velocity, according to the state of condensation and the weight of the body projected.

It consists of a lock, stock, barrel, ramrod, etc., of about the size and weight of a common fowling-piece. Under the lock at b is screwed a hollow copper ball c, perfectly air-tight. This ball is fully charged with condensed air, by means of the syringe B, previous to its being applied to the tube at b. Being charged and screwed on as above stated, if a bullet be rammed down in the barrel, and the trigger a be pulled, the pin in b will, by the spring-work in the lock, forcibly strike out into the ball, and thence, by pushing it suddenly, a valve within it will let out a portion of the condensed air, which, rushing through the aperture in the lock will act forcibly against the ball, impelling it to the distance of 60 or 70 yards, or farther if the air be strongly compressed. At every discharge only a portion of the air escapes from the ball; therefore, by re-cocking the piece another discharge may be made, which may be repeated for a number of times proportioned to the size of the ball. The air in the copper ball is condensed by the syringe B in the following manner: The ball is screwed quite close on the top of the syringe; at the end of the steel-pointed rod a is a stout ring, through which passes the rod k; upon this rod the feet should be firmly set; then the hands are to be applied to the two handles i i fixed on the side of the barrel of the syringe, when, by moving the barrel B steadily up and down on the rod a the ball c will become charged with condensed air, and the progress of condensation may be estimated by the increasing difficulty in forcing down the syringe. At the end of the rod k is usually a square hole, that the rod may serve as a key for attaching the ball to either the gun or syringe. In the inside of the ball is fixed a valve and spring, which gives way to the admission of the air, but upon its emission comes close up to the orifice, shutting out the external air. The piston-rod works air-tight by a collar of leather on it, in the barrel B ; it is therefore obvious that, when the barrel is drawn up, the air will rush in at the hole h ; when it is pushed down, it will have no other way to pass from the pressure of the piston but into the ball c at the top. The barrel being drawn up, the operation is repeated, until the condensation is so great as to resist the action of the piston.

In Gifford's air-gun, Fig. 158, the barrel is in communication with the inside of the trigger-box, in the interior of which is a valve-piston, consisting of a steel rod carrying a ring fitted with a caoutchouc disk for closing communication. Air enters the barrel by a bell-shaped chamber. By pressing strongly on the extremity of the rod, the disk is compressed and closes the reservoir-orifice. By suddenly releasing the piston-valve, the elasticity of the rubber, combined with the pressure of the air, causes the sudden opening of the reservoir-orifice, and emits a blast of air to the rear of the projectile. The air is compressed into a reservoir beneath the barrel by means of a piston working longi. tudinally in a valved interior tube.