The Galvani Electrode Potential

The surface potential of Hg can be evaluated by comparing the real potential aα; (negative work function) of different impurity ions, dissolved in Hg. The real potential of an ion is the sum of a chemical term, corresponding to the interaction energy with the Hg in the bulk of the phase (depending on the ionic radius), and a constant electrical term corresponding to the surface potential of Hg (independent of the ionic radius). An electrostatic model is developed to calculate the chemical term of the real potential. This chemical component becomes negligible for very large ionic radii, and the surface potential of Hg can be determined by extrapolation. A value of is obtained. The fact that is positive indicates that the surface dipoles of Hg are oriented with their negative poles against the vacuum. Using the free energies of hydration given by Latimer, a value of is calculated for the Galvani electrode potential of a N ‐calomel electrode This result compares with the value of 0.5 v quoted by Latimer, Pitzer, and Slansky. The latter authors neglected the surface potential of Hg.