Abstract: The electromotive forces of the following cells1. Ag|AgCl|HCl(m_A)+NH₄Cl(m_B)+H₂O|Glass-eleetrode2. Pt(black)|H2 (latm)|HCl(m_A)+NH₄Cl(m_B)+H₂O|AgCl|Ag have been measured at total molalities of 0.1, 0.5, 1.0, 2.0 and 3.0 mol.kg^-1 at 25℃. The potential of the glass-eteetrode was found not to be in agrtement with Nernst equation due to the effect from NH₄⁺.The unsymmetrical potential of the glass-electrode have been derived:ε_G^o=ε_G'^o+RT/FlN[1+Kα(1+βy^B)y^B/(1-y^B)] where y^B is malar fraction of NH₄Cl,ε_G'^o is unsymmetrical potential of glass-electrode at y^B=0. K is an equilibrium constant for ion-exchange, α and β are experimental parameters.

Key words: glass-electrode, unsymmetrical potential, ammonium ion