Vapour pressure over curved surfaces-the Kelvin equation

The exponential form of the Kelvin equation which relates equilibrium vapour pressure to surface curvature and surface energy has, until recently, remained unconfirmed. Previous efforts have been, in the main, directed to testing the first approximation of the equation. The present article reviews, briefly, some previous experimental work and gives an account of a new and successful effort to verify the more exact form of the equation. The method employs an electron microscope to observe the rates of evaporation, at suitable temperatures, of droplets of liquid metals of radii less than 50 nm.