22 FREILING, CROCKER, AND ADAMS Scholze, Mulfinger, and Franz.” Its solubility gives an indication of what can be expected for other noble gases. In the temperature range 1200 to 1480°C, these workers found a value of 8 ranging from 0.012 FRACTIONAL DEPARTURE FROM EQUILIBRIUM to 0.035. (For water at 0°C, 8 is 0.0094!) Solubility was favored by high 0 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 FRACTIONAL DISTANCE FROM CENTER TO SURFACE 0.90 1.0 Fig. 9—Diffusion of n° atoms into a sphere. Fractional departure from equilibrium as a function of reduced radius for various reduced times. Silica content and high temperature. Obviously, solubility alone is not a great consideration. | Vesicularity (the presence of gaseous occlusions) is a commonly observed property of fallout particles. In the larger particles the frac- tion of the volume due to occlusions has been observed to vary from 5 to 44%. This would raise the effective value of 8 to 0.06 to 0.46. Thus, although the factor of 10° to 10 in the ratio of vapor volume to soil volume at the time of particle formation prevents solubility and occulsion of rare gases from being important, they appear to be on the borderline of significance and may require consideration in extreme cases.