It is known that the surface tension of solutions of many hydrophilic colloids such as proteins, saponins and soaps, is comparatively high when the surface is newly formed and that it falls rapidly at first and then more slowly (du Noüy, 1919, 1926; Wilson and Ries, 1923; Harkins and Zollmann, 1926). This fall may continue for many hours and measurements of the surface tension of such a solution cannot therefore have much significance unless either the surface has reached equilibrium or the age of the surface is known. The method which is most frequently used for the study of the surface tension of such solutions is that which depends on the measurement of the force exerted by the liquid on a wire ring which is placed on the surface and then pulled away (du Noüy, 1926; Harkins and Jordan, 1930). It is the purpose of this paper and which is especially suitable for these studies. Certain curious reactions of the surface of solutions of stretching will also be described.
Design of a digital vision system for measuring surface tension.
