Ionic Radius and Ionic Efficiency. by Jacques Loeb

When pure water is separated from solutions of electrolytes of not too high a concentration (generally below ~/4) by a collodion membrane, the initial rate of diffusion of water through the membrane from the side of pure water to that of the solution is influenced in a characteristic way by ions and the following rules have been found to govern this influence. 1. Ions possessing the same sign of electrical charge as the membrane increase and ions with the opposite sign of charge diminish the initial rate of diffusion of water. 2. The relative influence of the oppositely charged ions is not the same for all concentrations. In the lowest concentrations of electrolytes the influence of the ions with the same sign of charge prevails, increasing at first with increasing concentration of the electrolyte until a maximum is reached; a further increase in concentration diminishes the rate of diffusion of water into the solution and the more so the higher the concentration of electrolyte. The turning point varies for different electrolytes but seems to lie for a number of neutral solutions at about ~/256 or above. 3. The influence of ions on the initial rate of diffusion of water from the side of pure water through the membrane into the solution increases with their valency and with a second constitutional quantity which in the, earlier papers I designated arbitrarily as the radius of the ions. I t will be shown in this paper that the second constitutional quantity seems indeed to be, for monatomic and monovalent ions, the radius of the ion and that the rule connecting the efficiency of ions with 673