Effects of Sunlight and Ammonia on the Action of Silver-Iodide Particles as Sublimation Nuclei *

Abstract

Tests involving exposure of AgI smoke to bright sunlight show a decrease in concentration of effective nuclei (at −20°C) of approximately two orders of magnitude per hour. The concentration of effective nuclei is increased greatly (as much as two orders of magnitude) by the addition of a little ammonia vapor to the AgI smoke. Smoke samples which have been deactivated completely by exposure to ultraviolet light can be caused to form large numbers of ice crystals by the addition of ammonia vapor. If ammonia is added before exposure to light, the rate of decay is the same or greater, and the effectiveness cannot be restored by further addition of ammonia. The effect of ammonia is believed to be due to the adsorption of ammonia on the silver iodide surfaces or to the formation of an ammine of silver iodide.