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Determination of Ionic Activities in Soil‐Water Systems by Means of the Donnan Membrane Equilibrium
Author(s) -
Peech Michael,
Scott A. D.
Publication year - 1951
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1951.036159950015000c0023x
Subject(s) - library science , soil water , citation , state (computer science) , sociology , chemistry , computer science , environmental science , soil science , algorithm
K of the ion activities in soil-water systems is essential to the proper understanding of the physico-chemical behavior of soils and the ionic environment of plant roots in the soil (4, 7). Prior to development of the clay membrane electrode by Marshall (4) little was known concerning the activities of exchangeable cations in soils although the "suspension effect" first demonstrated potentiometrically by Bradfield (1) with electrodialyzed clays constituted direct evidence of the dissociation of H+ ions in colloidal clay suspensions. Marshall (4, 5, 6) has successfully employed the clay membrane electrode to measure the activities of NH4+, Na+, K+, Ca++, and Mg++ ions in clay suspensions and has shown that the activities of the monovalent cations are much higher than those of the divalent cations at the same degree of base saturation. Unfortunately the clay membrane electrode lacks the desired specificity, and its use is therefore limited primarily to the measurement of cation activities in homoionic clay or soil suspensions, even though under favorable conditions Marshall (5) has extended this method to the determination of the activities of two coexisting cations in clay suspensions. In an effort to make possible simultaneous determination of the activities of any number of coexisting cations in soil water systems, a method based on the Donnan membrane equilibrium has been developed, and sufficient data have been obtained with clay suspensions to establish the validity of the method. In this paper, which is intended only as a preliminary report, a brief description of the method is presented together with some data on montmorillonite suspensions to illustrate the accuracy of the method as well as its utility in studies of ionic equilibria in clay or soil water systems.