54 LABORATORY LESSONS IN GENERAL SCIENCE 



PRESSURE EXERTED BY THE ATMOSPHERE 



1. Tie in loose folds some thin sheet rubber over the 

 large end of a thistle tube, making air-tight the rubber 

 covering. Blow into the open end of the tube and observe 

 the rubber. Compare the amount of air within the tube 

 now and before. What must be true of the condition of 

 the air within as compared with the air without the tube? 

 Explain why the rubber is pressed outward. 



2. Using the same apparatus, suck some of the air from 

 the tube and observe. Exhaust more of the air, and ob- 

 serve again. Explain why the rubber is now forced inward, 

 and why more in one case than in the other. What relation 

 exists between the density of the air within the tube and its 

 pressure upon the rubber? With the density of the out- 

 side air remaining the same, how may the greatest inequality 

 of pressure on the sides of the. rubber be secured ? 



3. Closely fit into a wide-mouthed bottle a rubber stopper 

 through which is passed two glass tubes, one of them long, 

 and the other short and bent at right angles. Let the 

 longer tube extend down into some water in the bottle. 

 Through the short tube blow gently into the bottle and 

 observe the water in the long tube. What change in con- 

 dition of the air in the bottle results from blowing more and 

 more air in ? Why does water rise in the long tube ? 



What relation exists between the degree of compression 

 of the air in the bottle and the height of the water column ? 

 What causes the rising column to come to rest? How long 

 will it remain stationary? 



Force water up into the long tube nearly to the top, and 

 close the tube air-tight with one of the fingers, leaving a lit- 



