SIPHON. 



177 



being forced through the other valve into the discharge 

 pipe. When next the piston is raised, the discharge pipe 

 valve is closed, preventing the return of the water above 

 it, while atmospheric pressure forces more water from below 

 into the barrel. 



297. The Air- Chamber of a 

 Force-Pump. Water' will be thrown 

 from such a pump in spurts, correspond- 

 ing to the depressions of the piston. A 

 continuous flow is secured by connect- 

 ing the discharge pipe with an air- 

 chamber. This air-chamber is provided 

 with a delivery pipe, the lower end of 

 which terminates below the surface of the 

 water in the air-chamber. When water is 

 forced into the air-chamber, it covers the 

 mouth of the delivery pipe, and compresses 

 the air confined in the chamber. This 

 diminution of volume of the air is attended 

 by a corresponding increase of tension 

 ( 284), which soon becomes sufficient to 

 force the water through the delivery pipe 

 in a continuous stream. 



FIG. 115. 



298. The Siphon. The siphon consists of a bent 

 tube, open at both ends, having one arm longer than the 

 other. It is used to transfer liquids from a higher to a 

 lower level, especially in cases where they are to be removed 

 without disturbing any sediment they may contain. It 

 may be first filled with the liquid, and then placed with 

 the shorter arm in the higher vessel, care being had that 

 the liquid does not escape from the tube until the opening 



