Electromotive force measurements have been made using the reversible formation cell Various aspects of the cell design are discussed. Measurements were of sufficient precision to give the concentration dependence and the magnitude of the excess free energies, enthalpies, and excess entropies of mixing in the systems. The results are discussed in terms of covalent bonding in molten silver chloride. A simple semiquantitative “dual bonding” model is developed in which “ionic” and “covalent” silver coexist.