Information on two molecular mechanisms of ice nucleation on saver iodide and silver chloroiodide particulates has been gained by a chemical kinetics interpretation of the rates and mechanisms of ice crystal formation from experiments conducted in a 1 m(3) isothermal cloud chamber. The interpretation required the consideration of the Langmuir surface adsorption of water molecules by ABI from the vapor and the chemistry of AgI colloids and suspensions in water with and without the influences of supporting electrolytes. One mechanism is a slow rearrangement of three-dimensional water molecule clusters, adsorbed at water saturation and -20 degrees C and lower on 500 Angstrom and larger substrate particles, to ice embryos. The second occurs rapidly at -5 to -20 degrees C on substrate particles wetted by liquid water. This mechanism is hypothesized to involve the rearrangement of ordered water molecule clusters associated with hydrated Ag(+ )ion patches on the substrate surface, The rate of nucleation is slowed by the presence of alkali and alkaline earth halides. Crystal structure match of the substrate with that of ice may help the first mechanism but, perhaps, has no effect on the second.