The incipient condensation of water vapour on a gold surface

An experimental investigation has been made of the incipient condensation of water vapour on gold by observations of light scattering. Results have been obtained for surfaces well washed by condensation and for surfaces which, after having been washed in this way, have been exposed to small amounts of room air. Nominally monochromatic light of two different wavelengths has been used, and hysteresis has been observed in the growth and subsequent evaporation of the incipient condensate. All the results are in general agreement with a theory which embodies Raoult's law, Kelvin's equation and the known optical scattering of dielectric spheres. Exposure to room air has resulted in very pronounced effects through the acquisition of water-soluble impurities. Even on the cleanest surface produced, residual water-soluble matter played an important role. The number of scattering centres (droplets) has been found to be practically independent of the amount of soluble impurity present. The agreement of the results with a theory which involves the adjustment of few parameters opens the way to further studies of the phenomena involved.