EXERCISE 3 A 

 DOES .VI I{ HAVE WEIGHT? 



Materials. An air pump (an inexpensive filter pump may be used) ; a brass globe ; a bottle or flask. 



Directions. This experiment may be performed by the teacher, 

 but each pupil should make his own solution of the problem and 

 write complete notes. 



Pump the air out of a brass globe or other container as com- 

 pletely as possible, and close the stopcock. Weigh and record 

 the weight of the globe. Open the stopcock to admit air, weigh 

 again, and record the weight. Has the weight changed? 



What is your answer to the question with which this exercise 

 began ? 



If the brass globe ordinarily used for this purpose is not 

 available, a bottle or flask may be used. This should be fitted 

 with a one-holed rubber stopper, through which is inserted a short 

 glass tube. A piece of thick-walled rubber tubing fitted with a 



pinch clamp will serve as a stopcock. The air may be removed by means of either an ordinary air 

 pump or a filter pump. The latter is inexpensive and entirely satisfactory if water under pressure 

 is at hand. 



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