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The pH Values of Soils Suspended in Dilute Salt Solutions¹

ABSTRACT

The pH values of dilute solutions and soils were measured with the standard glass-reference electrode combination and with the glass-silver, silver chloride pair without liquid junction. At low ionic strengths, the pH values of the soils and solutions determined with the glass-Ag, AgCl Combination were about 0.1 to 0.2 unit lower than those obtained using the standard reference electrode. With the soils, the differences were observed even when the KCl junction was kept in the clear supernatant liquid. Stirring the solutions and the soil suspensions and increasing the salt concentration decreased the pH values measured with the glass-reference pair but not with the glass-halide electrode combination. From these observations it was concluded that pH measurements made at low ionic strengths using the standard reference electrodes with restricted diffusion of KCl were subject to direct liquid junction errors. These liquid junction potentials were distinct from Donnan-electromotive force (emf) effects caused by interaction of the charged soil particles with the KCl junction. Like the Donnan-emf effects, they could be reduced by increasing the electrolyte concentration in solution.

¹ Contribution No. 130, Soil Research Institute, Canada Department of Agriculture, Ottawa, Ontario.

Received for publication April 6, 1965. Accepted for publication September 28, 1965.