CHAPTER XXII 

 WATER OR LIQUID PUMPS 



144. Influence of Air in Pumping Liquids. Air has 



weight and each square inch of surface at sea level is 

 holding up about 15 pounds of air, that is, the air exerts 

 a pressure of 15 pounds per square inch; 15 pounds of 

 pressure will sustain a column of mercury 30 inches 

 high. Since mercury is 13.6 times as heavy as water, 

 the air will sustain a column of water 34 feet high if there 

 is no air pressure on top of the water. When the air is 

 removed from a tube which is standing in water, the air 

 pressure on the water outside the tube will force the 

 water up the tube. When we drink a liquid through a 

 straw, we remove the air pressure from the end which is 

 in the mouth, and then the air pressing on the liquid in 

 the vessel forces the liquid up the straw. 

 But we could not drink water through a 

 tube 35 feet high. Why? 



145. The Siphon. The siphon may 

 be a U-shaped tube with the arm outside 

 the liquid longer than the arm extending 

 down into the liquid. The liquid in the 



tube is trying to flow in both directions 



J 6 THE SIPHON 



from the point C. The liquid in CD is 

 exerting a pressure on the liquid in the vessel, while the 

 liquid in CB is exerting a downward pressure greater 

 than that of CD, since it is longer than CD by AB. 

 When two unequal forces resist each other there is 



