10. A Valve for a Pump.
The following is the construction of the valve referred to. Take two rectangular plates of bronze of the thickness of a carpenter's rule, and measuring about one finger's breadth (7/10 of an inch) on each side. When these have been accurately fitted to each other, polish their surfaces so that neither air nor liquid may pass between them. Let A B C D, E F G H,(fig. 10) be the plates, and in the centre of one of them, A B C D, bore a circular hole about 1/3 of a finger's breadth (1/4 of an inch) in diameter. Then, applying the side C D to E F, let the plates be attached by means of hinges, so that the polished surfaces may come together. When the valve is to be used, fasten the plate A B C D over the aperture, and any air or liquid forced through will be effectually confined. For by the pressure exerted the hinges move, and the plate E F G H opens readily to admit the air or liquid; which when inclosed in the air-tight vessel, presses on the plate E F G H, and closes the aperture through which the air was forced in.