Abstract
Part I of this Thesis consists of a brief review of the past work carried out by physicists, chemists and meteorologists on naturally occurring fogs. It includes a description of the instruments and techniques used in the characterisation of fog, some of which have been adopted by the writer in studying artificial aqueous fogs. In Part II, methods are described for the preparation of aqueous fogs and a description of the experimental conditions found necessary to obtain reproducible systems is included. The fogs studied include those prepared from distilled water, tap water and aqueous solutions of sulphuric acid. The properties of fogs treated with small amounts of surface active agents are described and the relative stabilities of fogs of various types are assessed from sedimentation and light transmission experiments, and from measurements of drop-size distribution. The results indicate the dependence of fog stability upon the nature and number of ions present in the fog droplets. Empirical equations are derived which fit the experimental results and appear to indicate the presence of a droplet-to-droplet coalescence mechanism. The rate of coalescence between fog droplets is shown to decrease with increasing electrolyte concentration, and values are derived which, give a measure of the relative extent of the droplet-to-droplet coalescence.