Water, acetone and the normal alcohols from methyl to hexyl have been adsorbed on mercury. All substances gave reversible adsorption and, with the exception of water, gaseous films were formed at low pressures. Methyl and ethyl alcohols showed the adsorption of a second layer at higher pressures, the double layer having half the co-area of the original monolayer. Actone gave rise to a double layer and finally a triple layer (with one-third of the original co-area). The property of multilayer formation was thought to be one of small partially polar molecules. For the gaseous films of n-butyl, n-amyl and n-hexyl alcohols the co-areas and the thermodynamic data indicated that the molecules were lying flat on the surface. These three substances showed two-dimensional condensation to liquid films at higher pressures. This phase change was accompanied by an increase of entropy which led to a decrease of the surface-vapour pressure with rise of temperature. The large entropy and heat of adsorption of water were taken as evidence for the association of the adsorbed water molecules and this probably occurred, to some extent, with methyl alcohol as well. The heat of adsorption of acetone was smaller than expected for a substance with a large dipole moment.