A NEW APPARATUS FOR MEASURING SURFACE 

 TENSION. 



By p. LECOMTE du NOUY. 



{From the Laboratories of The Rockefeller Institute for Medical Research.) 

 (Received for publication, March 31, 1919.) 



Surface tension is probably one of the most difficult phenomena to 

 measure. Although a great deal of ingenuity has been spent for 

 almost a century in devising accurate techniques, the figures obtained 

 deviate more from each other for the same substance, according to 

 different authors, than any other constant characterizing the sub- 

 stance. It is well known that the two classes of methods of meas- 

 urement, the static and the dynamic give entirely different results 

 when applied to the same liquid. The following figures illustrate 

 these differences. 



Dynamic. Static. 



Water 73 73 



Sodium oleate 26 79 



Heptylic acid 54 68 



The static values were obtained by the capillary tube method, and 

 the dynamic values by the oscillating jet method. Nevertheless, 

 under given conditions, all the methods give practically concordant 

 values in the case of pure liquids, but not in the case of solutions. 



With the static methods (among which are weight of hanging 

 drops, rise in a capillary tube, adhesion of a disc to the surface, ex- 

 cess of pressure in a spheric bubble produced in a liquid, direct meas- 

 urement of curvature of the surface), the following figures are obtained 

 for. the surface tension of water. 



Dynes. 

 cm. 



Method of puUing off a ring 81 .0 



" " capillary tube (air) 75 . 5 



" " " (water vapor) 73.0 



521 ' 



