Corrections for surface tension measured by Wilhelmy method

Abstract

In the Wilhelmy method of surface tension measurement it is necessary to correct for (1) the lowering of liquid level caused by the meniscus formation when the liquid touches the hanging plate (meniscus correction) and (2) for the difference between the effective and geometrical peripheral length of the plate (peripheral correction). The application of these two corrections is studied for both water and toluene using a number of hanging glass plates and rods and platinum plates differing in the size and shape of their horizontal cross sections. The following empirical equation was obtained: σPM=σ[1−(sS)][1+(l0L)], where πP M denotes the surface tension corrected for the peripheral and meniscus errors, π is the observed surface tension, S is the surface area of a liquid in a vessel, s and L are the cross-sectional area and peripheral length of the hanging plate and rod, and l0 is the constant for the peripheral correction. The values of l0 are from −0.008 to −0.010 cm for plates, −0.005 cm for triangular rods, and zero for cylindrical rods. These values are independent of the peripheral length and material of the plates or rods.