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Electromotive-force measurements of the cell $$Pt;H_2 (g, 1 atm)|HCl (y_A I), CsCl (y_B I)|AgCl;Ag$$ for five values of the ionic strength (I) between 0.1 and 3.0 mol-kg-1 and over the temperature range 5 to 50°C are reported. At I=1.0 and above, the activity coefficients of HCl are a distinctly non-linear function of solution composition. This behavior is satisfactorily accounted for in terms of specific ion interactions of the type H-Cs and H-Cl-Cs. The temperature variation of the Harned coefficient supports the suggestion of Robinson that the interaction H-Cs is insensitive to temperature changes.

The activity coefficient of hydrochloric acid has been determined in HCl-KCl-H2O mixtures at 25°C and for seven values of the ionic strength between 0.1 and 3.0 mole-kg-1, using the cellPt;H2(g, 1atm)\HCl(mA),KClBAgCl;Ag

The activity coefficient of HCl (?A) in aqueous mixtures of HCl and LiCl was determined by emf measurements of cells without liquid junction at five values of the total ionic strength, namely 0.1, 0.5, 1.0, 2.0, and 3.0 mol-kg-1 (m), and at nine temperatures from 5 to 45°C. The ionic strength fraction (?B) of LiCl in the mixtures was varied from 0 to 0.9. The values of log ?A were found to vary linearly with the molality of salt, in accordance with the ‘Harned rule,’ indicating that the properties of these mixtures are determined primarily by binary ionic interactions of the type H-Li and that ternary interactions are not significant even at I=3m. The results also support the suggestion of Robinson that the interaction parameter ?H,Li is insensitive to temperature changes when I is less than 2m.