IONIC RADIUS AND IONIC EFFICIENCY. 



By JACQUES LOEB. 



{From the Laboratories of The Rockefeller Institute for Medical Research) 



(Received for publication, May 4, 1920.) 

 I. INTRODUCTION. 



When pure water is separated from solutions of electrolytes of not 

 too high a concentration (generally below m/4) by a collodion mem- 

 brane, 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 wav bv ions and the following rules have been found 

 to govern this influence. 



1. Ions possessing the same sign of electrical charge as the mem- 

 brane 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 electro- 

 lytes 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 m/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. 



It will be show^n 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 



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