OF THE AIR-PUMP. 219 



13. Set the square phial A upon 

 the pump-plate, and having covered 

 it with the wire-cage B, put a close 

 receiver over it, and exhaust the air 

 out of the receiver ; in doing of 



which, the air will also make its way out of the phial 

 through a small hole in its neck under the valve b. 

 When the air is exhausted, turn the eock below the 

 plate, to re-admit the air into the receiver ; and, as it 

 cannot get into the phial again, because of the valve, the 

 phial will be broken into some thousands of pieces by 

 the pressure of the air upon it. Had the phial been of 

 a round form, it would have sustained this pressure like 

 an arch, without breaking ; but as its sides are flat, it 

 eaunot. 



To shew the Elasticity or Spring of the Air. 



14. Tie up a very small quantity of air in a bladder, 

 and put it under a receiver ; then exhaust the air out of 

 the receiver ; and the small quantity which is confined 

 in the bladder (having nothing to act against it) will 

 expand itself so by the force of its spring, as to fill the 

 bladder as full as it could be blown of common air 

 But upon letting the air into the receiver again, it Will 

 overpower the air in the bladder, and press its sides 

 almost close together. 



15. If the bladder, so tied up, be put into a wooden 

 box, and have 20 or 30 pounds weight of lead put upon 

 it in the box, and the box be covered with a close re- 

 ceiver ; upon exhausting the air out of the receiver, that 

 air which is confined in the bladder will expand itself 

 so as to raise up all the lead by the force of its spring. 



16. Take the glass ball, mentioned in the fifth experi- 

 ment (page 213,) which was left full of water all but a 

 small bubble of air at top, and having set it with its 



