Experiments on the contact angle of water on ice

The results of two new experiments designed to determine the contact angle of water on ice are reported. In one it is shown that the first stage of melting of a clean ice surface is liquid formation at discrete sites, not uniformly over the surface as would be predicted if the contact angle were zero. The water has a downward meniscus and a sharp contact angle against the ice during both melting and freezing. In the second experiment ice discs are grown in water at approximately 0·010°C supercooling, and contacted by air bubbles on their smooth, basal faces. According to this experiment the contact angle of water on ice is zero. These contradictory results may be a result of anisotropic surface energy, or an effect of disequilibrium.