Societies and Academies

Abstract

LONDON. Faraday Society, December 13.—Sir Robert Hadfield, Bart., president, in the chair.—Prof. E. D. Campbell: A force field dissociation theory of solution applied to some properties of steel. Understanding of the properties of alloys has been obscured by the use of the term “solid solution” and by expressing constitution in terms of percentage weights. There is no essential difference between a liquid and a solid solution, and the constitution of both should be expressed as molecular or atomic concentrations per unit volume. The electrolytic dissociation theory in its usual form is inapplicable to alloys. The force field theory is a modified form of it applicable to liquid and solid solutions alike. The assumption is made that in a molecule the electromagnetic force field associated with the constituent atoms is closed in the combination, but in solution this force field is opened out by the solvent to an extent depending on concentration and composition. The reactivity of ions is due to the open force fields, and not to the presence of electric charges. In the presence of an impressed e.m.f. the resultant of the reactivity is electrical resistance in the case of metallic solutions, and electrical conductance in aqueous solutions.—A. L. Norbury: The electrical resistivity of dilute metallic solutions. It is well known that the small quantities of impurities in solid solution cause a large increase in the electrical resistivity of a pure metal. Data are collected showing the relative atomic effects of such impurities, and a certain relationship appears to be brought out by doing so. The author summarises his conclusions as follows:—(1) A comparison with the atomic volumes, intrinsic pressures, electrical resistivities, thermo-electric properties, and decomposition potentials of the elements concerned shows that none of these atomic properties can be directly applied to explain the results. It is suggested that the atomic effects are small when there is little electrical attraction between the atoms of solute and solvent, and large according as the electrical attraction between the two is greater. (2) It seems probable that in the dilute solutions quoted the atoms of solute are not associated. (3) Assuming, for example, the face-centred cube lattice in a dilute solid solution, an atom of solute will be surrounded by twelve equidistant atoms of solvent, and will not be attached to any one of these atoms in particular. It will, therefore, exert attractive forces on the electrons of the surrounding atoms. (4) It is generallv assumed that metals conduct the electric current by means of their “free” electrons; the presence, therefore, of forces restraining the “free” electrons in solid solution will account for their diminished conductivity.