Among the various techniques employed to study the state of water present in ion exchangers, vapour pressure isotope effect during the dehydration of different ionic forms of the exchanger provides useful information on the primary and secondary hydration shells around the ions and their temperature effect. The hydration numbers obtained by analyzing the water sorption isotherms by D'Arcy and watt equation are in consonance with those obtained for these ions in exchanger phase and electrolyte

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... lutions. These information can be used to understand the nature of electrolyte solutions and the ion exchange selectivity.