Adsorption of Air and Water Vapor on Rock-Salt Surfaces

With a method previously described the adsorption of air on rock-salt surfaces is measured as a function of temperature, and the temperature at which complete outgassing occurs is determined. An estimate of the thickness of the film is given, and also the approximate speed at which it forms. The effect of water vapor on the surface is observed, and it is shown that exposure to water vapor has no permanent effect on the surface as long as the partial pressure of the water vapor is kept below that of a saturated sodium chloride solution at the same temperature. This, however, is true only of cleavage surfaces; polished surfaces are less stable against the action of water vapor.