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Ion Diffusion: I. A Quick-Freeze Method for the Measurement of Ion Diffusion in Soil and Clay Systems¹

ABSTRACT

The method combines a radioisotope-tracer technique for measuring ion distribution by quick-freezing the exchange medium and sectioning it into 50µ segments with a refrigerated microtome. Ten-50µ sections were placed in separate counting pans for a quantitative radiation assay. From these data the distribution resulting from ion diffusion in montmorillonite and kaolinite clays and Sharkey and Dundee soils was obtained.

The accuracy of the freezing and sectioning method was determined by using replicate-radioactive cores in which ion diffusion had not occurred. These cores were sectioned, counted for radiation, and then weighed. The coefficient of variation for the weight of clay or soil sections was 1.89, 2.14, 2.27, and 3.70% for kaolinite, montmorillonite, Dundee silt loam, and Sharkey clay, respectively. Coefficients of variation in the activity of the sections of exchange media were 2.39, 2.80, 3.18, and 1.29%, respectively. The coefficient of variation in the apparent diffusion coefficient for Rb⁸⁶ in replicated cores of kaolinite clay was 6%.

¹ Contribution from the Agronomy Department, University of Arkansas, Fayetteville. Presented before a joint session of Div. S-1 and S-2, Soil Sci. Soc. Am., Denver, Colo., Nov. 20, 1963.

² Professor, Research Assistant, and Assistant Professor in agronomy, respectively.

Received for publication March 11, 1964. Accepted for publication June 4, 1964.