18 LABORATORY EXERCISES 



two-quart fruit jar or a tall vase will do. Fasten a small vial 

 or test tube (mouth downward) to a wire or stick, and push it 

 slowly to the bottom of the water. What happens to the vol- 

 ume of the air in the vial or test tube? Why? What relation 

 does there seem to be between the depth of the water and the 

 pressure of the water? 



b. The Diver. Arrange the bottle and other apparatus 



; shown in Fig. 10. The vial is partly full of air and 



partly of water; it should just float. Put the stop- 

 per tightly into the bottle, and blow air through 

 the tube. What is the result? Then let the extra 

 air escape. What happens to the vial? Now, in- 

 stead of blowing air into the bottle, remove air, by 

 suction, from the bottle, and tell the result. 



What is the explanation of the behavior of the 

 vial? Draw three sketches showing the position of 

 the vial, and of the air and water in it, at ordinary 



FIG. 10. 



pressure, at increased pressure, and at reduced 

 pressure/ Compare the behavior of the diver with that of a 

 submarine boat. 



EXERCISE 14 

 COLLECTING A GAS OVER WATER 



Apparatus and Materials. Wide-mouth bottle (small), pan of water, 

 glass tube, wooden splinter, test tube, illuminating gas. 



a. Fill a wide-mouth bottle completely with water, and 

 cover the mouth of the bottle with a piece of wet writing paper. 

 With your hand hold the paper in place, so that no air bubbles 

 remain in the bottle. Then invert the bottle over a pan of 

 water, but do not, at first, put it into the water. If you are 

 careful, you can remove your hand from the paper, and the 

 water will not fall out. What supports the water? 



