Ice Nucleation Behavior of Silver Iodide Smokes Containing a Soluble Component

Abstract

The ice nucleation behavior of smokes consisting of silver iodide, together with a soluble component such as potassium iodide, is considered theoretically. It is proposed, when released into a natural cloud, that the smoke particles take up water to form solution droplets in each of which is suspended a small particle of silver iodide produced by hydrolysis of the mixed salt. If the temperature is low enough, this silver iodide particle may nucleate the freezing of the solution droplet. This process is treated thermodynamically, and the nucleation activity of the smoke particles is calculated as a function of size. It is found that the behavior is insensitive to the nature and exact concentration of the soluble component. Theoretical curves for the activity of such a mixed smoke are derived and show good agreement with experiment. This treatment supersedes the author's 1959 calculation based on the assumption of sublimation activity.