On the Solid Condensation Nucleus Which is not Soluble in Water

Studies on the Formation of Cloud and Rain III

Abstract

So far the solid nucleus which is insoluble in water has been treated in the same way as the water drop of the same size in condensation processes, and it has been considered that such nucleus cannot act as condensation nucleus in the atmosphere, because the maximum water vapour pressure on it is higher than that on the hygroscopic nucleus. However, when such nucleus is wetted fairly well by water the adhesive force of water to the solid nucleus is larger than the cohesive force of water, hence the maximum water vapour pressure on the solid nucleus is lower than that on the water drop of the same size. Therefore, it is clear that such nucleus can act as condensation nucleus more effectively than the water drop of the same size.
The author investigated thermodynamically the stability of the thin water film formed on such a solid nucleus and obtained a formula which expresses the saturated water vapour pressure on the film, namely where k: Boltzmann's constant, P_{_??_, h}, maximum water vapour pressure in equilibrium with the water film with thickness h formed on the spherical solid nucleus with radius R, P_∞: maximum water vapour pressure on the plane water at the absolute temperature T, σ: surface tension of water, υ_B: molecular volume of water, ε: ratio between the adhesive force of water to the solid nucleus and the cohesive force of water, U_∞: evaporation energy of water of large mass referred to one molecule, δ₁₁: distance between two neighbouring water molecules.
From the above result it was found that the solid nucleus which is wetted well by water and is larger than 10^-5cm can act as condensation nucleus in the atmosphere.