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The Use of Thermometric Titrations in Soil Chemistry Studies¹

ABSTRACT

It was determined that a thermometric titration procedure could be used to obtain the cation-exchange capacities and heats of neutralization of acid-saturated clays. The endpoints of these titration curves were much sharper than those commonly obtained by potentiometric or conductometric methods.

Cation-exchange capacities calculated from thermometric titration curves of H-exchanges agreed fairly well with those determined by the BaCl₂-TEA method. Heats of neutralization for Arizona, Mississippi, Southern and Utah bentonites were found to be: –13.3 ±2, –15.9 ±3, –16.1 ±1 and –15.5 ±2 kcal. per eq., respectively. The heat of neutralization of humic acid was –13.2 ±1 kcal. per eq. and that of Al-saturated Mississippi bentonite was –5.5 kcal. per eq. The large difference in the heat of neutralization of the H- and Al-saturated exchangers causes titration curves for the two to have widely differing slopes. This allows determination of the proportions of H and Al saturations of mixed H-Al clays from the titration curves.

The possible use of thermometric titrations in determining the course, mechanism and rate of a number of chemical reactions in soils is discussed and concluded to be excellent.

¹ Published with the approval of the Director, Pennsylvania Agr. Exp. Sta., as Paper No. 2536 in the Journal Series. Presented before Div. II, Soil Sci. Soc. Am., Dec. 7, 1960, at Chicago, Ill.

² Assistant Prof. Soil Technology, Agronomy Dept., Pennsylvania State University, University Park. Now Assistant Professor of Agronomy, University of Kentucky, Lexington.

Received for publication March 20, 1961. Accepted for publication May 3, 1961.