56 LABORATORY LESSONS IN GENERAL SCIENCE 



calculate what height of water column would be supported 

 by the same atmospheric pressure. 



5. If possible make a study of a mercury barometer, not- 

 ing in it (a) the mercury cistern and how the air pressure 

 from without reaches the mercury surface; (b) the heights 

 of the mercury column from time to time, and from what 

 point this measurement is taken in all cases ; (c) the provision 

 for reading the height of the mercury column to the fraction 

 of an inch. 



What would be the effect of the presence of any air within 

 the tube (a) upon a rising barometer column; (6) upon a 

 falling column? 



APPLICATIONS OF ATMOSPHERIC PRESSURE 



1. Tightly close the mouth of a tall bottle with a rubber 

 stopper through which passes a pipette whose small end is 

 inside the bottle. Attach a short piece of rubber tubing to 

 the large end outside the bottle, and with the mouth by 

 repeated efforts exhaust the air from the bottle, pinching 

 the tube together while taking breath. Put the end of the 

 rubber tube under water, and holding the bottle bottom 

 up release the pressure on the rubber tube. Explain the 

 action noted. What causes it to stop? 



2. Hold by the bottom a tumbler brimful of water. Press 

 down closely upon the top of it a piece of cardboard, and 

 then carefully invert the tumbler. Remove the hand from 

 the cardboard, and explain why the water does not fall out. 



3. Insert one end of a glass tube into water and suck air 

 from the other end. Explain why the water rises in the tube. 

 What is a familiar application of this principle? 



