680 IONIC RADIUS AND IONIC EFFICIENCY 



monovalent cations increases. Fig. 3 shows that in the case of mono- 

 valent cations the depressing effect is least in the case of K, and 

 increases in the following order, K < Na < Li. 



In these experiments the solutions were almost neutral (hydrogen 

 ion concentration about 10~^ n). The order of efficiency of the cations 

 remains the same when the solutions of these salts are made up in 

 n/ 1,0.00 KOH and when the distilled water in the outside solution 

 is replaced by n/1,000 KOH; since in this case the membrane is 

 also negatively and the water positively charged. Fig. 4 shows that 

 the depressing effect of the monovalent, monatomic cations increases 

 in the order Rb < K < Na < Li, where the depressing effect is 

 least in the case of Rb, and greatest in the case of Li. This order of 

 the depressing influence of cations is independent of the anion used 

 as long as the anion is always the sam.e for the different cations used. 

 Thus Fig. 5 shows the same order of the depressing action of cations 

 for nitrates as in Fig. 4 in the case of the chlorides. 



Since this is also the order in which the ionic radius of the four 

 ions diminishes (Rb having the greatest ionic radius) we can make 

 the following statement. 



The depressing effect of monatomic, monovalent cations on the 

 rate of diffusion of positively charged water through a negatively 

 charged collodion membrane from the side of pure water to the side 

 of the salt solution increases inversely with the order of magnitude 

 of the radius of the cation. 



III. Positively Charged Membranes. 



It has been shown in preceding publications that when the mem- 

 brane is positively and the water negatively charged the cations 

 increase and the anions diminish the rate of diffusion of water from 

 the side of pure water through the membrane into the solution. In 

 order to make a membrane, previously treated with gelatin, positively 

 and the watery phase of the double layer negatively charged it is 

 necessary to give the water and the solutions a hydrogen ion concen- 

 tration of about 10~^ N or above. We made the solution acid by 

 dissolving the salts in 10 "^ n HNO3 and the distilled water outside 

 the collodion bag was also replaced by lO^^ n HNO3. The hydrogen 



