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Certain Physico-Chemical Properties of the Pinchen Clay and the Function of Its Free Iron Oxide and Organic Matter¹

ABSTRACT

Tension-moisture content relationships of the deferrated soils and control soil indicated that available moisture was reduced from 10.3% to 7.3% as the result of deferration.

From the study of vapor adsorption isotherms, the constants of the BET equation were derived. Deferration increased the standard free energy of adsorption of water on the bare surface, F°₁, and decreased the specific surface, S, while oxidation decreased both F°₁ and S. The deferrated clay was dispersed easier by humic acid, showed less buffering effect against Ba(OH)₂, and a decrease in exchange capacity; whereas oxidized clay gave a stronger buffering effect against NaOH. The energy of replacement of Ca by K showed no difference between variously treated clays, indicating binding force of cations at exchange sites was little affected by presence of organic matter or iron oxide.

It was concluded that the principal clay minerals and free iron oxide forming fine porous coating might be regarded as the dominant factors affecting moisture and surface characteristics of the Pinchen clay.

¹ Contribution from the Department of Agricultural Chemistry, National Taiwan University, Taipei. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. degree. The authors are grateful to Prof. G. B. Bodman, University of California, Berkeley, for reading the manuscript and giving valuable criticisms.

² Research Associate and Professor of Soils, respectively.

Received for publication October 28, 1958. Accepted for publication January 20, 1959.