i8 



Common Science 



FIG. 8. A siphon. The air pushes the water over the side of the pan. 



so strong outside the balloon, and so the gas inside makes 

 the balloon expand until it bursts. 



Experiment 9. Lay a rubber tube flat in the bottom of 

 a pan of water, so that the tube will be filled with water. 

 Let one end stay under water, but pinch the other end 

 tightly shut with your thumb and finger and lift it out of 

 the pan. Lower this closed end into a sink or empty pan 

 that is lower than the pan of water. Now stop pinching 

 the tube shut. This device is called a siphon (Fig. 8). 



Experiment 10. Put the mouth of a small syringe, or 

 better, of a glass model lift pump, under water. Draw 

 the handle up. Does the water follow the plunger up, 

 stand still, or go down in the pump? 



When you pull up the plunger, you leave an empty 

 space; you shove the air out of the pump or syringe 

 ahead of the plunger. The air outside, pressing on the 



