486 ELECTRICAL CHARGES AND ANOMALOUS OSMOSIS 



the salt on E begins at lower concentrations than the depressing action 

 on €, it follows that the electrical transport of water must at first rise 

 with increasing concentration of the salt and then drop. 



4. If the Donn'an equilibrium is the sole cause for the p.d. (e) 

 between solid gelatin and watery solution the transport of water 

 through collodion-gelatin membranes from water to salt solution 

 should be determined purely by osmotic forces when water, gelatin, 

 and salt solution have the hydrogen ion concentration of the isoelec- 

 tric point of gelatin (pH = 4.7). It is shown that this is practically 

 the case when solutions of LiCl, NaCl, KCl, MgCl2, CaClo, BaCL, 

 Na2S04, MgS04 are separated by collodion-gelatin membranes from 

 water; that, however, when the salt has a trivalent (or tetravalent ?) 

 cation or a tetravalent anion a p.d. between solid isoelectric gelatin and 

 water is produced in which the wall assumes the sign of charge of the 

 polyvalent ion. 



5. It is suggested that the salts with trivalent cation, e.g. Ce(N03)3, 

 form loose compounds with isoelectric gelatin which dissociate elec- 

 trolytically into positively charged complex gelatin-Ce ions and nega- 

 tively charged NO3 ions, and that the salts of Na4Fe(CN)6 form loose 

 compounds with isoelectric gelatin which dissociate electrolytically 

 into negatively charged complex gelatin-Fe(CN)6 ions and positively 

 charged Na ions. The Donnan equilibrium resulting from this ioni- 

 zation would in that case be the cause of the charge of the membrane. 



