Evidence of long range force in capillary phenomena

Abstract

Working with two superposed liquid layers such as benzene-water I had difficulty in obtaining reproducible values for the capillary constant of the aqueous layer.This could have been due to the difficulty in establishing equilibrium between the saturated liquid and its vapor. T o minimize this effect I began to work with short capillaries. The capillary rise began to diminish with flattening of the meniscus. Several cm of length of the capillary above the meniscus were necessary to reach the maximum value of the capillary rise. Further increase had no effect. As dy/dc (where y is surface tension and C is the concentration) in aqueous layer is enormous, a part of the above effect may be due to the change of concentration.Experiments with pure water, made by R. J. Conan in my laboratory at Fordham University showed similar effects: only to give maximum rise, the length of the capillary above the meniscus, was found to be about 0.2 cm (see drawing).Such an effect, as far as evidence goes, is shown by polar liquids. Liquids like benzene do not show it to an appreciable degree. Capillary rise at the interface water-ether definitely showed dependence on the length of the capillary. 0.2 cm is well above the magnitude of the radius of molecular action. beyond which the attractive forces are no more supposed to be effective. Presence of a long range force throws a new light on capillary rise as a means of measuring the surface tension.The experiment should be understood as follows: ,The force of attraction 1) between the solid and the liquid is greater than that between the particles of the liquid itself. The film of the liquid fixed on the wall of the capillary is capable of supporting a column of a liquid determined by its surface tension. It is not equal to 2 m y , where 1) G.