62 



UXPhJBfMhWTS WITH PLaXTS 



an inch and a halt' of the top with fresh syrup. Fit 

 a small rubber cork to the tube and push it down 

 about half an inch into the tube; insert a 

 needle at one side of the cork, so as to allow^ 

 the compressed air to escape and restore the 

 normal pressure. Withdraw the needle and 

 carefully dry out tlie inside of the tube 

 above the cork. Melt some sealing-wax in 

 a spoon, and pour it slowly into the tube 

 until it runs over. With a hot knife smear 

 it over the outside as far down as the cork, 

 so as to close the tube air-tight (see Fig. 52) . 

 Obtain or prepare a strip of paper ruled in 

 fine divisions (millimeters or twenty -fourths 

 of an inch, if possible), and gum it to the 

 upper part of the tube for the purpose of 

 measuring the length of the air- column in 

 the tube. Place the tube in water, note the 

 length of the air -column, and observe it fre- 

 quently during the experiment. The amount 

 of pressure produced in the tube can be 

 easily calculated from the amount of com- 

 pression which the air undergoes. The for- 

 mula for the calculation is : 



52. Apparat\is 

 for measur- 

 ing the pres- 

 sure due to 

 osmosis. 



Lenjjth of air-eoluran at start = Pressure at finish, 



Length of air-oolnmn at finish Pressure at start. 



Thus, if the colunm measure one inch at 



