i86

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Fig. 8.

Of the Air-Pump.

to pump out the air. As the air goes out of thereceiver by its spring, it will also by the samemeans go out of the hollow ball eb, through theneck dc, and rife up in bubbles to the surface ofthe water in the phial; from whence it will mak eits way, with the rest of the air in the receiver,through the air-pipe GG and valves a and b, intothe open air. When it has done bubbling inthe phial, the ball is sufficiently exhausted; andthen, upon turning the cock k, the air will getinto the receiver, and press so upon the surfaceof the water in the phial, as to force the waterup into the ball in a jet, through the neck cdiand will fill the ball almost full of water. Thereason why the ball is not quite filled, is becauseall the air could not be taken out of it; and thesmall quantity that was left in, and had expandeditself so as to sill the whole ball, is now condensedinto the same state as the outward air, and re-mains in a small bubble at the top of the ball >and so keeps the water from filling that part ofthe ball.

6. Pour some quicksilver into the jar D, andset it on the pump-plate near the hole i; thenset on the tall open receiver AB, so as to be overthe jar and hole; and cover the receiver with thebrass plate C. Screw the open glass tube fg(which has a brass top on it at h) into the syringeH, and putting the tube through a hole in themiddle of the plate, so as to immerse the lowerend of the tube e in the quicksilver st D, screwthe .end h of the syringe into the plate. Thisdone, draw up the piston in the syringe by thering/, which will make a vacuum in.the syringe, >below the piston; and as the upper end of thetube opens into the syringe, the air will be di-lated in the tube, because part of it, by its spring,

o-ets