"The factors of atomic size, ion core potential, and charge, which contribute to the increment in electrical resistivity produced by solutes in metallic solutions, were separated and experimentally evaluated in liquid sodium. The results are expressed in a semi-empirical relationship which defines the increment in resistivity of a monovalent solution as the sum of the fractional difference in atomic volume of solute and solvent and the difference in atomic number of Na and the solutes Li, K, Cs, Rb, Ag, and Au."