116 INTRODUCTION TO GENERAL SCIENCE 



pressure. If we place a tube in a liquid, we may suck the air 

 out of one end of the tube, but the liquid will not come up the 

 tube unless the atmospheric pressure can act upon its surface. 

 Even if the atmospheric pressure is free to act upon the surface 

 of water, the latter will not rise more than 34 feet, as that is 

 the limit of the height of a water barometer. See Section 82, 

 Atmospheric Pressure and the Barometer. A rise of 34 feet 

 would require that there be a complete vacuum above the 

 water in the tube. 



References : 



1. 1803 : 59. Explanation of "Suction.", 



a. 1804 : 167. Suction. 



Experiment 44. " Suction." 



Apparatus : Test tube 8" by I 7 ', rubber stopper with two 

 holes. Glass tube to fit one hole. 



a. Fill test tube with water; insert stopper. Placing finger 

 on the empty hole in stopper, suck on tube. 



What happens? Why? Remove finger and suck again. 

 Explain. 



85. PUMPS 



Pumps are of two classes, the lift pump and the force pump. 

 In the lift pump the effec t of atmospheric pressure is made use 

 of; that is, the action of the pump is the same as in the case of 

 a person who is " sucking " on a tube. The atmosphere may 

 be said to push on the other end. A pump, then, if perfect, 

 cannot lift water higher than 34 feet. The usual pump can- 

 not lift over 28 feet. 



The force pump may be purely a force pump, in which case 

 it is placed below the surface of the water, or it may be a com- 

 bination lift and force pump. The height to which a force 



