EXPERIMENTAL INVESTIGATIONS ON THE ICE-FORMING ABILITY OF VARIOUS CHEMICAL SUBSTANCES

Abstract

A careful survey of the methods for measuring ice nucleation was made. Errors of previous investigations based on the relationship between the time lag of ice formation and the falling velocity of ice particles through a temperature gradient zone were avoided. Experiments were made on a large number of chemicals by using a thermostat-type cloud chamber, the threshold temperatures for ice nucleation of these chemicals were determined precisely and found to be somewhat higher than those of previous workers. Analysis of the experimental data shows the following: 1. the highly effective nuclei are all insoluble in water; 2. particles with the greatest structural similarity to ice make the most effective nuclei; 3. the stronger the ionic nature of nuclei crystals, the more effective are they as ice nuclei. These latter two factors are mutually inter-dependent. An explanation of the mechanism of ice formation is presented.