to the sprayer of fig1 by means of a constant delivery gear pump at a rate of 20 grams per minute the sprayer of fig1 was modified so as to permit flow only through the bottom tier of orifices each orifice having an inside diameter of 0 0135 inch the dope or solution was pumped through each orifice at a rate of 0 833 gram per minute and the sprayer was rotated at a speed of 3600 rpm the aerosol of pbi droplets formed were precipitated and collected in a bath of methanol the spherical microporous product was separated from the solvent rich methanol by filtration and washed with water to remove residual dimethyl acetamide the product had particle size diameters in the range of 50 150 microns with the particle size measurement and statistics listed below in table 1 table 1______________________________________ mean particlerun diameter standard variabilitynumber microns deviation coefficient ______________________________________1 91 35 90 39 662 82 35 75 43 773 104 39 86 38 224 97 29 20 30 11______________________________________ the standard deviation determination as employed above and in subsequent examples estimates the range of particle sizes in any system where randomness is observed it is useful to model the outcomes of measurements of a given property such as particle size and then apply the model as a predictor of the future behavior of that property typically such systems exhibit after a number of observations a most.