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and 1.15, for increasing molecular weight fractions, respectively. Furthermore, the reported uncertainty in individual Mw and Mn values is such that, in all cases but one, Mw/Mn could be as small as unity, giving a monodisperse fraction, with no violation of the stated precision. The one exception is the high molecular weight fraction, Mn = 735,000, for which the polydispersity effect well exceeds our experimental results at either extreme of the Ew/Mn ratio. This could possibly be explained if there were a high molecular weight tail to the distribution curve which might become lost in the base line without contributing to the apparent plate height. Further study is being conducted on this and related questions.

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An apparatus for determining the uniformity of a layer of fine particles deposited on a membrane filter is described. A transmission scan of a laser beam across the filter deposit is a measure of the uniformity of the deposit layer. Quantitative estimates, with an accuracy of approximately 10%, of areal densities are inferred by calibration against reference deposits of ground orchard leaves on membrane filters.