Emf measurements have been made In cells without liquid Junction of the type Pt,H2(1atm)|HX(m1),MX(m2)|AgCl,Ag, containing mixtures of (I) Ha and CH2(OH)CH2N(CH3)3Cl and (U) HCI and CH2(OOCCH3)CH2N(CH3)3Cl In different proportions, but at constant total Ionic strength (µ = 3, 2, 1, 0.5, 0.25, 0.1). Measurement have been carried out at 10 °C Intervale, over the temperature range 5-35 °C. The Ag-AgCl electrodes, prepared by the thermoelectrolytlc method, used In pairs for each measurement, gave results which closely agreed. The values for the standard electrode potential, E°, and the Interaction coefficient, α12, for each constant total Ionic strength mixture at aH of the four temperatures have been evaluated by the computerized least-squares method. Interpretation of the results has been made In terms of the multicomponent Ionic equilibrium theory of Seatchard (“neutral electrolyte as components treatment) and of Pfizer. © 1981, American Chemical Society. All rights reserved.