PROPERTIES OF CASES 



07 



is accomplished by means of a rubber tubing or bent glass 

 tubing with unequal arms. This apparatus is called a siphon. 



The principle of the siphon is explained as follows: In order to 

 start the siphon it is necessary first to remove the air from it. This 

 is done either by filling the siphon with water and placing a thumb 

 at each end of the siphon, then placing the smaller end in the water 

 that is to be removed from the vessel, or by drawing the water up 

 through the long end of the tube. The water in the tube is 

 driven toward the longer arm by a force equal to the difference 

 in the weight of the water in the two 

 arms. The difference in the lengths of 

 the arms should be great enough to over- 

 come the friction in the pipe and the 

 weight of the water in the short arm. 

 When this happens the water falls out of 

 the long arm and tends to leave a vacuum 

 at the top, but atmospheric pressure forces 

 the water up the short leg to fill this space. 



The tube ABCD (Fig. 60) is a siphon. 

 The shorter leg AB is put into the liquid 

 E, which is to be drawn off into G. If the 

 air be taken out of the tube the pressure 



FIG. 60. Siphon. 



of the air on the surface of the liquid E will force the liquid up 

 the tube AB, and it will then fill the whole tube and continue to 

 run until all the liquid in E has run into the vessel G. 



Questions 



1. Why do clothes dry more quickly on a windy daj^ than on 

 a quiet day? 



2. Does sprinkling the street on a hot day make the air cooler? 

 If so, why? 



3. In what part of the summer is the heat oppressive? Explain. 



4. What becomes of the cloud of steam that escapes from the 

 exhaust pipe of a power plant or a blowing locomotive whistle? 



5. When does moisture gather on a water pipe? Why? 



6. Why does the morning fog disappear usually before noon? 



