Applicability of the Drop-weight Technique to the Determination of the Surface Tensions of Liquid Metals

Abstract

The drop-weight (drop-volume) technique is one of the standard methods for the determination of surface and interfacial tensions. Although the empirically determined correction factors used in the calculations are based on liquids with densities in the range 0.1 to 2.2 gm cm–3 and surface and interfacial tensions up to 72 dyn cm–1, the method is commonly used for liquids, such as liquid metals, whose physical constants are outside of this range.

The present work was carried out to determine the applicability of the drop-weight correction factors of Harkins and Brown to liquid metals. Pure mercury was used in a series of dropping experiments; drops, falling from a range of glass orifices in nitrogen, being measured. These results were then used to determine values for correction factors, using surface tensions in 1 dyn cm–1 intervals between 450 and 490 dyn cm–1. With a surface tension value of 471 ± 2 dyn cm–1 a correction curve was generated which agreed very well with the Harkins and Brown data in the range 0.720 ⩽ψ(r/V⅓)⩽ 0.615. The value of 471 ± 2 dyn cm–1 also agrees well with the most probable value deduced by Wilkinson as the surface tension of mercury.

Harkins and Brown did not determine correction factors above 0.720 80, so the results for mercury in the range 0.870 ⩽ψ(r/V⅓)⩽ 0.720 can only be compared with the theoretical curve of Lohnstein and some recent experimental work by Wilkinson on the extension of the correction factors for wetting liquids (e.g. water, organic liquids). The results for mercury do not agree with either data. Reasons for this lack of agreement, namely the inapplicability of the general principle of similitude (with reference to dropping) to all liquids or to the difference in correction factors for small orifices (large correction factors) between wetting and non-wetting liquids, are discussed.