The rate of change with concentration of the capacity of the electrical double layer on mercury has been measured. From this there have been calculated Γ+, the excess of cations in the double layer, and Γ—, the excess of anions. The latter has been subdivided into η—d, the excess of anions in the diffuse double layer, and η—i, the excess of anions in the inner part of the double layer. From these data it has also been possible to evaluate ψ0, the potential of the outer Helmholtz plane. It is found that fluoride ion remains unadsorbed on mercury at all potentials investigated, including potentials anodic to the e.c.max. Other anions are strongly adsorbed (chemisorbed) when the mercury is positively charged, and sometimes even when it is negatively charged. The ``hump'' in the capacity curves of salts of such anions as chloride, bromide, acetate, and nitrate, are found to be present in curves of C—, the capacity attributable to anions alone. No chemisorption of monatomic cations could be detected. The kinetic theory of the diffuse double layer with constant dielectric constant is found to fit the experimental results within the expected accuracy. This fit extends to electrolytes of the 1:2 and 2:1 types also. A new method of evaluating salt adsorption at the potential of the electrocapillary maximum (e.c.max.) is described and results are given. Likewise a new method of determining C+ at the e.c.max. is described and used.
Procedures, based on the methods of Madelung, have been developed for the evaluation of lattice sums of inverse-power particle-interactions, λa—n, at any point in or near a cubic crystal. Although not as elegant mathematically as those of Hove and Krumhansl, they are more complete in including the important cases of a point near a plane or line of particles, and are sufficiently simple in principle to be understood and applied by anyone with a background in differential calculus. Applications to a face-centered cubic ionic crystal are discussed and, as an example, the dipole-dipole van der Waals energy of a chloride ion before a NaCl half-crystal is calculated.
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