HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Coleman, N. T. Articles by Jakobi, W. J. Search for Related Content PubMed Articles by Coleman, N. T. Articles by Jakobi, W. J. Agricola Articles by Coleman, N. T. Articles by Jakobi, W. J.

Ion Activities and Osmotic Pressures in Clay-Water Systems¹

ABSTRACT

Osmotic pressures of H-, Na-, and K-bentonite suspensions were measured with an Adair osmometer. Measurable osmotic pressures were observed, but the values were quite small, ranging from 0.6 cm H₂O for 1% Na-bentonite to 4.2 cm H₂O for 4% H-bentonite. The ion activity difference across the osmometer membrane, calculated from the membrane potential and the ion concentration on the solution side, was large. The ionic osmotic pressure difference across the membrane, from the van't Hoff approximation, was much larger for all systems than was the observed osmotic pressure, leading to the conclusion that the membrane potential cannot be regarded as a measure of an electrostatic potential difference between a clay suspension and its equilibrium dialysate.

Electrolyte mean activities of KCl solutions were consistently slightly smaller than in 2% K-bentonite suspensions of the same normality of KCl. Mean activities of KCl in the clay suspensions were much smaller than K⁺ activities measured with a membrane electrode-saturated calomel electrode cell.

The osmotic pressure data and potentiometric data are interpreted as indicative of a spurious potential at a clay-salt bridge junction.

¹ Contributed from the Dept. of Agronomy, North Carolina Agri. Expt. Stat. Published with the approval of the Director as Paper No. 478 of the Journal Series. Presented before Division 2, Soil Science Society of America, Cincinnati, Ohio, Nov. 20, 1952.

² Associate Professor of Agronomy and former Graduate Assistant, respectively.

Received for publication June 1, 1953.