The sound of a bell is much louder in condensed than in common air. A phial that would bear the pressure of the com mon atmosphere, when the air is exhaust ed from the inside, will be broken by con densing the air round it. These experi ments may be made under the receiver B.
A very beautiful fountain may be made by condensed air. Procure a strong cop per vessel, (fig. 10) having a tube that screws into the neck of it, so as to be air tight, and long enough to reach near to the bottom. Having poured a quantity of water into the vessel, but not enough to fill it, and screwed in the tube, adapt to it a condensing syringe, and condense the air in the vessel ; shut the stopcock, and unscrew the syringe, then, on open ing the stop-cock, the air acting upon the water in the vessel, will force it out into a jet of very great height. A number of different kinds of jets may be screwed on the tube, such as stars, wheels, &c. form ing a very pleasing appearance.
The air-gun is a pneumatical instru ment, of an ingenious contrivance, which will drive a bullet with great violence, by means of condensed air, forced into an iron ball by a condenser. Fig. 11, repre sents the condenser for forcing the air into the ball. At the end of this instru ment is a male screw, on which the hol low ball, b. is screwed, in order tube fill ed with condensed air. In the inside of this ball is a valve, to hinder the air, after it is injected, from making its escape, un til it be forced open by a pin, against which the hammer of the lock strikes ; which then lets out as ranch air as will drive a ball with considerable force to a great distance.
When you condense the air in the ball, place your feet on the iron cross, h It, to which the piston-rod, d, is fixed ; then lift off the barrel, e a, by the handles, i until the end of the piston is brought be tween e and c; the barrel, a c, will then be filled with air through the hole, e. Then thrust down the barrel, a c, by the handles, i i, until the piston, e, join with the neck of the iron hall at a ; the air be ing thus condensed between e and a, will force open the valve in the ball, and when the handles are lifted up again, the valve wilt close and keep m the air, in this man ner the hall will presently be filled; after which, unscrew the ball offthe condenser, and screw it upon another male screw, which is connected with the barrel, and goes through the stock of the gun, as re presented, (fig. 12 ) The whole will be better understood by (fig. 13.) which is a section of the gun. The inside, k, is that from which the bullets are shut, and, C D S R, is a larger barrel, In the stock of the gun, M, which forces the air through the valve E P, into the cavity be •tween the two barrels, dive is a valve at S L, which being opened by the trig. ger, 0, permits the air to rush suddenly behind the bullet, so as to drive it out with great force. If the valve is sudden ly opened and closed, one charge of con densed air may make several discharges of bullets.