Floating Mercury on Water

Abstract

IN a letter in NATURE of Mar. 16, Mr. N. K. Adam describes the floating of small globules of mercury on a water surface, even when the latter was considerably contaminated. He concludes that for equilibrium to be possible, the mercury-air tension must have been reduced by the order of one or two hundred dynes. It is not necessary to suppose such a decrease. It appears that the part played by curvature of the surfaces in determining conditions for the equilibrium or the spreading of one liquid on another has been neglected. Experimentally, we have the observations of Burdon (Proc. Roy. Soc., 38, 2, 154; 1926), who found that water would spread over the surface of a large, clean mercury drop, but that its progress was stopped when the curved edge of the drop was reached, where acceleration ‘downhill’ would be expected.