Dissolution patterns of polydisperse powders: oxalic acid dihydrate

The dissolution of oxalic acid dihydrate crystals of log-normal particle-size distribution in 0.1 N HC1 was studied. A biphasic cube root dependence was found; the slopes of the initial cube root plots were consistent with theory based on dissolution of isometric, isotropic particles where assumptions were made of: (a) sink conditions, (b) particle-size-independent solubility, and (c) particle-size-independent film thickness of adsorbed liquid layers.