4 6 



pressure in the short arm must be one atmosphere. 

 Measure the distance be between the top of the mercury 

 and the closed end of the tube. 



(b) Pour more mercury into the open end of the tube, 

 and, as the mercury rises higher and higher in the long 

 arm, note carefully the decrease in the volume of the air in 

 the short arm. Pour mercury into the tube until the dif- 

 ference in level bd is just equal to the barometric height, 

 approximately thirty-two inches. The pressure of the air 

 in the closed end now supports the pressure of one atmos- 

 phere and, in addition, a column of mercury equal to an- 

 other atmosphere. 



Measure carefully the distance between the mercury 

 level in the short arm and the closed end of the tube. 

 What effect has the doubling of the pressure had upon 

 the volume of air in the short end ? 



If the tube were long enough to make the mercury 

 column in the open end just three times as high, the pres- 

 sure in the long arm would be three times that of the 

 atmosphere. What effect would this have upon the volume 

 of the air in the short arm ? 



State a law which will show the effect of pressure upon 

 the volume of a gas. This is known as Boyle's Law. 



Why will a toy balloon explode if too much air is forced 

 into it ? Why do steam boilers sometimes burst ? 



