182 ELECTRIFICATION OF WATER 



The facts given are not peculiar to sodium salts but can be demon- 

 strated in the case of all neutral or alkaline solutions of salts with 

 monovalent or bivalent cation. Fig. 5 gives the curves for different 

 chlorides and Fig. 6 for different sulfates. All the curves for these 

 salts rise up to a concentration of about m/256 and then fall and finally 

 rise again when the concentration is so high that the gas pressure ef- 

 fect begins to obliterate the electrical effect of the ions. The turn- 

 ing point for the commencement of the prevalence of the gas pressure 

 effect is at a lower gram-molecular concentration for the sulfates than 

 for the chlorides; Fig. 3 shows that the concentration of the turning 

 point is the lower the higher the valency of the anion. It may be 

 that this is simply the consequence of the fact that the higher the 

 valency of the anion the greater the number of ions into which the 

 salt dissociates electrolytically, but it is not yet certain that this is the 

 full explanation. Another fact, however, is certain; namely, that the 

 depression of the curves when the concentration exceeds m/256 is 

 greater for the hthium salts than for the sodium salts, and greater 

 for the sodium salts than for the potassium salts. This was to be 

 expected if the drop is due to the repelling action of the cation on the 

 positively charged particles of water, since the repelHng action of 

 cations on the positively charged particles of water increases inversely 

 with a quantity which we arbitrarily designate as the "ionic radius." 

 This "ionic radius" is less for Li than for Na and presumably less 

 for Na than for K. 



In the case of neutral solutions of salts with bivalent cation the re- 

 pelHng action of the cation is so great that it balances or exceeds the 

 initial attractive action of a bivalent or monovalent anion for posi- 

 tively charged particles of water; the depressing action of the cation 

 in concentrations above m/256 upon positively charged particles of 

 water remains, however, noticeable especially in the SO4 curves, 



//. Influence of the Concentration of Electrolytes upon the Rate of Dif- 

 fusion of Negatively Charged Particles of Water through 

 Collodion Membranes. 



The curves given in Figs. 3 to 6 contain a paradoxical fact, which 

 can be expressed as follows : when solutions of neutral or alkaline salts 

 ivith monovalent or bivalent cation are separated by a collodion membrane 



