AIR AND WATER AS SERVANTS OF MAN 



129 



Put lengths of glass tubing into the cork, the end of one flush 

 with the inner end of the cork, the end of the other reaching 

 nearly the bottom of the bottle. Put a valve over the end that is 

 flush with the cork so that it will let water in. Connect this one 

 by a short length of rubber tubing to the outlet of the squirt 

 gun, now to be used as a force pump. Connect a short rubber 

 tube to the outlet of the small bottle and put a pipette glass into 

 the other end of this rubber tube. Then 

 operate the pump and a steady stream 

 will issue from the pipette " nozzle." 



When the handle of the ordinary 

 pump is brought up (see Fig. 51) the 

 plunger is forced down in the cylinder, 

 the air escaping through the valve in it. 

 When the handle is forced down the 

 plunger rises, the valve closes at once, 

 and so a vacuum tends to form under 

 the plunger. The pressure of the air 

 on the surface of the water forces the 

 water part way up the pipe. The valve 

 in the bottom of the pipe lets the 

 water in but prevents its escape as the 

 plunger descends again. This process 

 is repeated until the water rises to the 

 plunger, when it flows through the 

 valve opening as the plunger is forced down. The water is then 

 raised above the plunger until it flows out of the spout. If the 

 plunger and valve get dry so they leak air, they must be made 

 air-tight by "priming" the pump, pouring water into the pump 

 from above. Such a pump cannot work when the distance from 

 the plunger to the surface of the water in the well is over 33 feet. 



FIG. 51. Diagram of a lift 

 pump. 



