175 



Ttie Surface Teistsion Temperature Coefficient. 



By Arthur L. Foley. 



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Some fifteen years ago the author described a method of finding the 

 surface tension of liquids by determining with a balance the force required 

 to pull a frame of mica from the liquid.^ A mica frame, cut in the form 



shown in Fig. 1 is suspended from one arm 



of a sensitive balance and the lower edge 



(a-b) of the upper strip of mica is brought 



into contact with the liquid. The liquid is 



then gradually lowered while the pointer of 



X I Q. 1. the balance is kept at the turning point by 



adding weights to the other pan. Eventually 



the downpull of the liquid and film is exceeded by the weights on the other 



arm of the balance, the mica frame is pulled suddenly upward, and the 



film brealvs. The frame is then weighed while still in the liquid. The 



difference between the two weights gives what is called the maximum 



weight, from which the method takes its name. 



The surface tension is given by the equation 



rp _ wg I dPf-'g itg ■,,,,,, I . n ^\A rn 



Where T=surface tension in dynes. 

 w=maximum weight. 



l=length of frame (between legs). 



t=thickness of frame. 



d=density of liquid. 



g=acceleration due to gravity. 

 When the frames are thin one may use the simple equation 



T = ^. (2) 



The maximum weight can be determined again and again with sur- 

 prising uniformity. Even when one uses mica frames differing greatly in 



1 Proceedings of the Indiana Academy of Science, 1895, p. 67. 

 Physical Review. Vol. 3, No. 5. 1806, p. 381. 



