132 ELEMENTS OF GENEEAL SCIENCE 



pressure will force the water up the pipe and against the 

 piston. If the pipe is tot) long the water may not reach 

 the cylinder; it will stand at such a height that the down- 

 ward pressure in the pipe, due to the weight of the water, 

 will be equal to the atmospheric pressure outside. Since, 

 as noted above, the height to which the atmospheric pressure 

 will raise a column of water is about 33 feet, the suction 

 pipe should not exceed this length. 



150. Transmission of pressure in liquids. In a squirt gun 

 the pressure which is applied to the liquid by the aid of a 

 piston or a rubber bulb is transmitted to the liquid in the 

 nozzle and shoots the liquid out. In a similar manner the 

 pressure applied to the stopper of a bottle completely filled 

 with water may result in breaking the sides of the bottle. In 

 a city water system the pressure exerted by the pumps at the 

 pumping station is transmitted throughout the system and 

 may be discovered in the pressure of the water at any faucet. 

 The working of many common appliances, such as water 

 motors, lawn sprinklers, and fire engines, depends upon the 

 transmission of pressure by water. 



The transmission of pressure by liquids is utilized for the 

 application of great force by means of the hydraulic press. 

 This machine consists essentially of two communicating 

 cylinders, each containing a closely fitting piston, one of the 

 cylinders being of larger diameter than the other (fig. 67). 

 If the diameters of the cylinders are such that the area of 

 the end of one piston is ten times that of the other, it will 

 be found that if a pressure of 1 pound is applied to the water 

 in the smaller cylinder by means of the piston, the pressure 

 exerted by the water against the larger piston will, if friction 

 is ignored, be sufficient to support a weight of 10 pounds ; 

 that is, the force exerted by the second piston will be greater 

 than the force applied to the smaller piston by as many 

 times as the area of the larger piston is greater than the area 

 of the smaller one. This rule holds for cylinders and pistons 



