AbstractColumns packed with Bio‐Glas (porous glass manufactured by Bio‐Rad Laboratories, Richmond, California) of varying porosities were made which had the same cumulative pore volume. The pore radii were equal to or larger than the mean end‐to‐end distance of the 160,000 molecular weight polystyrene molecule in carbon tetrachloride. The efficiency of these columns was studied for the elution of polystyreneMw= 160,000 and two sharp polyisobutene fractions havingMn= 114,700 and 145,700. Elution volume was found to be independent of flow rate below a flow rate of 1 ml/min for all columns studied. Two pairs of columns with the differing cumulative pore volumes were compared, and only small differences were found in their efficiencies, as measured by the number of theoretical plates per foot. The pore size distribution is important in that it determines elution volumes and the effective separating range of the column, but it does not appear to materially affect the efficiency of the separation
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