Physicochemical Investigations of Clay‐adsorbed Organic Colloids: II

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Abstract
The purpose of this study was to determine the sedimentation velocity and free diffusion behavior of humic acid extracted from Miami clay with neutral sodium pyrophosphate solution. In addition the organic colloids extracted from several soils of the Miami catena were analyzed using the eletrophoretic technique.The electrophoresis examination indicated that the organic colloids extracted from the clay fractions of a Brookston, Crosby, and Miami soil were similar. In all cases it appeared that the extract consisted mainly of dark colored humic acid, with two additional colloids present in very small quantities.The sedimentation velocity and free diffusion study showed that the humic colloid isolated from Miami clay was polydisperse with respect to particle size. The following data were obtained for the colloid dissolved in a water solution:Sedimentation constant s20 2.8 × 10‐13 cm/sec/dyneDiffusion constant D20 3.9 × 10‐7 sq cm/secPartial specific volume V 0.67Frictional coefficient f/f0 2.3Weight‐average molecular weight Mw 53,000