MEASUREMENT OF SURFACE TENSION 



45 



1. By means of the torsion balance (Fig. 8) the force necessary to 

 lift a ring, plate or straight wire from the fluid-air interface is 

 determined. 



Fig. 8. — Du Xouy's Surfacp Tension Ai)paraliis. One ruble centiiiutre of tlie liiniid to 

 be tested is plaeed in tbe wateli-glass. The force re(|uireil to luill a platinum ring 

 from the fluid snrfaee is applied by twisting a wire The amount of torsion, and 

 hcnee the value of the surface tension, is given on the graduated dial. 



2. Drop-weight Method (Part II., p. 517). The weight of a drop 

 falling Ijy gravity under standard conditions (size of dropping 

 surface, etc.) gives a measure of the tension on the surface of the 

 drop. 



