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Published in Soil Sci Soc Am J 17:31-34 (1953)
© 1953 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Physicochemical Investigations of Clay-adsorbed Organic Colloids: II1

F. J. Stevenson, Q. Van Winkle and W. P. Martin2

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 x 10-13 cm/sec/dyne

Diffusion constant D20 3.9 x 10-7 sq cm/sec

Partial specific volume V 0.67

Frictional coefficient f/f0 2.3

Weight-average molecular weight Mw 53,000

NOTES

1 Contribution from Department of Agronomy, Ohio State University, and Ohio Agricultural Experiment Station. Published with permission of Director as Journal Article No. 5-53. Presented before Division III, Soil Science Society of America, Cincinnati, Ohio, November 19, 1952.

2 Research Fellow in Agronomy, Assistant Professor of Physical Chemistry, and Professor in Agronomy, resepectively.

Received for publication December 1, 1952.




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