The assumption has been made in preceding papers that, at a given concentration of 1:10,000, in the vessels used in our experiments, a monomolecular oriented layer was formed. Such a layer might be supposed to prevent the free escape of water molecules from the surface into the air, at least to a certain extent.
In order to check this assumption, the rate of evaporation of solutions of serum at different concentrations was measured. It was found that, under the conditions of the experiments, in a progression of dilutions from 10–1 to 10–6, the slowest evaporation took place at a concentration of 1:10,000. In a few cases (less than 20 per cent), evaporation was slower at a different concentration, but always within the same range (between 10–3 and 10–5), not far from 10–4.