rounded to three significant figures and lower activities to the nearest hundred c/m. Dashed lines representing the 95% confidence bands of the regression lines are also included. are given in the figures, where: The equations of the regression lines A = median activity in well c/m at H + 300 (Shot 8) or H + 12 (Shot A) Da == mean projected area diameter in microns Dn == mean maximum diameter in microns CONCLUSIONS In view of the limited data no generalizations can be made; however, the results do warrant the following observations: 1. An extensive range of activities is associated with each size and size-type group. The field data indicate that the activities of a size-type group containing 30 or more particles follow a normal distribution. 2. The field data also show that the activity of irregular particles varies approximately as the square of the diameter, a surface area function. For spheroidal particles the activity varies with a function exponentially greater than a volume function. In the case of dendrite-like particles the activity varies with a function exponentially greater than the irregular particle function. Approved bys ER. Somplein) E. R. TOMPKINS Head, Chemical Technology Division For the Scientific Director 26

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