A simple and convenient method has been derived for estimating the water activities, aw, of the aqueous solution containing electrolytes 1, 2,... , k by the following relation: where a^oo is the water activity of a solution containing only the electrolyte k at the same ionic strength as the mixture; /T is the total ionic strength of the mixture and Ik is the ionic strength of the electrolyte k in the mixture. In the systems HCl-NaCl-H2O, HCl-BaCl2-H2O, HCI-NaClO4-H2O, HCl-Ba(ClO4)2-H2O,

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... O4-H2O and HCl-NaClO4-Ba(ClO4)2-H2O, the water activities calculated by the above relationship agree within 2 %deviation with the experimental results obtained from measurement of water vapor pressures by the dynamic method using a gas chromatograph.