The Cause of the Suspension Effect in Resin‐water Systems

Abstract

Abstract Two hypotheses persist regarding the cause of the suspension effect. The traditional hypothesis attributes the effect to a different activity of ions in the suspension than in the dialyzate. The alternative hypothesis attributes the effect largely to a junction potential at the calomel‐suspension boundary. Data obtained by means of three independent methods in this investigation indicate that the latter hypothesis is correct. A potentiometric technique indicated that activities of chloride ions cannot be reliably measured directly in resin‐water systems due to the uncertainty of a junction potential which may be negligibly small or may be as high as several hundred millivolts. Osmotic pressure and freezing point determinations provided confirmatory evidence that the activity of ions was virtually identical in slurry and dialyzate even though the suspension effect was exceptionally large.