preciable extent at lower flow rates. This finding gives rise to the interesting observation that, for constant-surface pellets, the system is, in a sense, more "homogeneous" at lower agitation intensities. Determination of solvent flow patterns in the dissolution chambers at different flow rates would aid in the selection of proper flow rates for any particular system. Such studies, using the method described by Withey and Bowker (7), are in progress in these laboratories.
Comparison of Methods-The inherent deficiencies of the beaker method are essentially absent with the flow method. First, after defining the cell size, the only variable under nonturbulent flow conditions is the flow rate. Even under turbulent flow conditions, the problems seen with the pellet are reduced with disintegrating tablets, since the granules are usually small enough to circulate throughout the dissolution chamber.
Second, in light of the importance of low agitation intensities, it is encouraging to see (Fig. ) that flow rates of less than 10 ml./ min. with the 25-mm. cell yield agitation intensities lower than those provided by the three-bladed stirrer at 50 r.p.m. The inherent advantages of the flow method are emphasized by the fact that the lower flow rates needed for more laminar flow are most likely to yield meaningful in vitrci-in vivo correlations.