AN EXTENSION OF THE SCHULZE-HARDY RULE TO ASYMMETRIC ELECTROLYTES

The Schulze-Hardy rule for the determination of the critical coagulation concentration (CCC) of counterions is examined for the case of an asymmetric electrolyte solution, For a negatively charged surface, this rule predicts that the CCC ratio for cations of valences 3, 2, and 1 follows the ratio 3(-6):2(-6):1(-6), Or about 1:11:729, We show that for a common monovalent anion, a more precise CCC ratio for cations is 1:15:1118. More often than not, the deviation in the experimentally observed CCC ratio from that predicted by the Schulze-Hardy rule is attributed to experimental error, We show that, depending upon the type of electrolyte used and the magnitude of the surface potential of dispersed colloidal particles, this deviation can be inherent. (C) 1995 Academic Press, Inc.