Advantages and limitations of the grooved Wilhelmy plate

Abstract

A detailed analysis has been made of the grooved Wilhelmy plate as an instrument for measuring surface and interfacial tensions. It is shown, on the assumption of V-shaped vertical grooves, that the method can lead to errors if the weight of the dry plate is used as the reference force. In practical cases the error can be of the order of 1%. Quantitative expressions are given for the correction factor to be employed. It is also shown that no correction factor is required, providing one takes as the reference force the weight of the plate after it has come to equilibrium with the vapour phase, and capillary condensation of vapour in the grooves has taken place. This equilibrium will not readily be realized in practice, and an alternative procedure is proposed which utilizes the weight of the plate after it is detached from the liquid. The conclusions may also apply, at least semi-quantitatively, to randomly roughened, rather than regularly grooved, plates.