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High Frequency Titrimetry of Soils and Clays: Methodology, Theory, and Nature of the Ba-Mg Exchange Reaction¹

ABSTRACT

A highly sensitive method for studying cation-exchange phenomena was developed. A high frequency titrimeter, sensitive to about 0.0002 me., was used along with a continuous-delivery buret of precision ±0.0003 ml. Soil or clay samples of 0.5 to 2.0 g. (much less can be used) were first saturated with Na, then converted to Ba-saturation, and finally titrated in semiaqueous media with standard sulfate solution.

The apparent dissociation of Ba from exchange sites is indicated by comparisons with titration curves for strongly dissociated (BaCl₂) and weakly dissociated (Ba-(OAc)₂) salts. For many soils and clays, four general stages or regions of the curve can be differentiated. These appear to represent loose bonding, moderate bonding, moderately strong bonding, and very strong bonding. The bonding characteristics of exchangeable Ba are further illustrated by curves of a few selected soils and reference clays. These curves also demonstrate: (1) similarities in clay-mineral behavior between specific soil samples and reference clays; (2) differences between reference clays in the same group; and (3) differences between arable soils and those developed in hydromorphic environments.

¹ Scientific Article No. A949. Contribution No. 3312 of the Maryland Agri. Exp. Sta., College Park. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree. Grateful acknowledgement is made to the Soil Survey Laboratories, SCS, USDA, for some of the soil samples used; and to O. E. Street, Univ. of Maryland, for final drafting of figures 2–10. Presented before Div. II, Soil Science Society of America, Nov. 30, 1961, at St. Louis, Mo.

² Graduate Student and Associate Professor of Agronomy. The senior author now is a Research Soil Scientist, SCS, USDA, Beltsville, Md.

Received for publication February 5, 1962. Accepted for publication August 28, 1962.