This paper concerns condensation of submicroscopic water droplets on hydrophobic substrates in a hydration chamber and then replication of water droplets by SiO vapor. In the first approach, the water‐vapor pressure was adjusted in relation to the temperature of the carbon substrate. At or below the relevant equilibrium saturation vapor pressure, no replicas of droplets were seen in low magnification fields. Above the saturation value many replicas of water drops were seen at a similar magnification. The number and distribution of the droplets increased with increasing level of supersaturation. In the second approach, the water droplets were labeled by the addition of 120‐A˚ diam ferritin molecules or 880‐A˚ polystyrene latex spheres. These droplets were deposited by spraying labeled water. Alternatively, droplets were settled on grids from sonicated emulsions of iso‐octane and labeled water. The iso‐octane was allowed to evaporate off in a saturated water‐vapor atmosphere leaving the labeled droplets on the grid. One grid was replicated by SiO in the wet state and the other was allowed to dry to show a circle of the droplet markers corresponding to each water droplet. The comparison at low magnification of the replicated droplet distribution and the circumscribed deposits of label clearly showed that it was water droplets that were being replicated. The mechanism of formation of a film of SiO on a low‐viscosity liquid‐water surface has been explained on the bases of current theories of solid‐state nucleation.
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