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I I I I I I I I I I I I I I I I I I I 15 mechanism of ice formation. Effectivity was increased in water supersaturated environments, turther supporting the conclusion that their nucleant functioned by a condensation-freezing mechanism. The temporal rate of ice formation has been shown to be a vital element in the deduction of nucleation mechanisms (DeMott, et al., 1'83, Horn, et al., 1'82, and Reiss, 1'82). The interpretation of observed rates of nucleation in past studies has been inadequate and, at times, have been ignored in spite of gross shifts in rates with slight changes in oondi tions. Such is the case when AgI tirst became known as an ice nucleant. The rate ot ice cr,ystal production by AgI aerosol produced by combustion of an AgI-IfH..I-acetone solution in a small cloud chamber was observed to decrease exponentially with time and required about 55 ainutes (Vonnegut, 1''''). The rate ot AgI nucleation was oompared to the rate of ice tormation due to the use of a pop gun. When a pop gun is used in a cloud chamber containing supercooled cloud, the rapid expansion ot air trom the gun causes spontaneous (homogeneous) nucleation. The rate of ice cr,ystal tormation by the pop gun was reported as non-exponential with time (actually, the rate is linear with time), and ice crystal tallout was complete in about 8 minutes. Vonnegut attempted to explain the phenomenon by asserting that ice embryo tormation on the AgI particle is a random process that depends on chance. He reasoned that because of certain energy requirements, surface energy relative to free energy, the probability of ice embryo formation increases with decreasing temperature. Thus, nuclei which normally function instantaneously at colder temperatures require more time to function at warmer temperatures. This hypothesis conflicts with Vonnegut's statement that the rate of ice nucleation by AgI did not