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The Significance of Potentiometric Measurements Involving Liquid Junction in Clay and Soil Suspensions
Author(s) -
Peech Michael,
Olsen R. A.,
Bolt G. H.
Publication year - 1953
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/sssaj1953.03615995001700030008x
Subject(s) - chemistry , suspension (topology) , potentiometric titration , ion , diffusion , membrane , drop (telecommunication) , soil water , analytical chemistry (journal) , chromatography , thermodynamics , soil science , geology , organic chemistry , telecommunications , biochemistry , physics , mathematics , homotopy , computer science , pure mathematics
A critical study has been made of the behavior of the liquid junction between the saturated KCl and the clay or soil suspension in attempt to evaluate the sign and the magnitude of the junction potential in measurements of membrane potentials and ion activities. In deflocculated suspensions of clay saturated with monovalent cations, the saturated KCl in the salt bridge short‐circuits the potential drop across the diffuse double layer and thus exaggerates the magnitude of the membrane potential or the ion activity of the clay suspension predicted by the Gouy theory. In suspensions of Ca‐clay and most soils, however, the effect of short‐circuiting the small potential drop across the diffuse double layer is more than offset by the diffusion potential due to CaCl 2 that is formed ahead of the KCl diffusion front. The sign of this diffusion potential is such as to decrease the magnitude of the membrane potential or the ion activity of the clay suspension. Comparison of the observed osmotic pressure of clay suspensions with that calculated according to the Gouy and the Donnan theories fully confirmed the conclusions reached from the potentiometric data concerning the sign and magnitude of the liquid junction potential.