Liquid Surface Tension near the Triple Point

It is shown that the product of the isothermal compressibility $\xi$ and surface tension $\Sigma$ of a liquid near its triple point may be expected to be a fundamental length characteristic of the liquid. From experimental data on 30 liquids (including liquid metals) it is observed that while $\xi$ and $\Sigma$ separately vary by a factor of 150, the product $\mathrm{\xi \Sigma }$ varies by a factor of less than 3 and is equal always to a few tenths of an angstrom unit.