The Determination of Surface Tension by Sessile Drop Measurements, with Application to Mercury

Abstract

The error in the Worthington (1885) sessile drop equation, as an approximation to the exact equation from which it was derived, is found to be of the order of experimental errors in recent surface tension determinations. The source of error and origin of the optical band system observed when parallel light is used to define the summit of a sessile drop have been investigated. The band system is shown to originate in an interference phenomenon from the curved surface of the drop. Detailed descriptions are given of the cleaning and testing methods necessary for the preparation of mercury and glassware involved in the determination of the surface tension of mercury as 484·9 ± 1· 8 dyn./cm. A lower limit to the temperature coefficient of the surface tension was set at 0·20 dyn. /cm. °C.