740 ELECTRIFICATION AND DIFPUSION OF WATER 



VII. Direct Proof of the Influence of the Valency and Radius of Ions 

 on the Sign of the Charge of Water. 



Experiments on the migration of water through a collodion mem- 

 brane under the influence of a constant current (electric endosmose) 

 furnish the direct proof that our assumption is correct. 



It is known that if a current is sent through the walls of a porous 

 cell bounded on both sides by the same liquid conductor, water mi- 

 grates either to the cathode or the anode. This migration is indi- 

 cated by a rise in the level of the water on the side of that electrode 

 towards which the water migrates. Helmholtz explained this phe- 

 nomenon by the formation of an electrical double layer at the bound- 

 ary of the diaphragm and the water particles. When a current is sent 

 through the liquid the positively charged particles of water will move 

 towards the cathode and if the water particles in contact with the 

 wall are negatively charged they will move towards the anode. On 

 account of the internal friction of the liquid the neighboring layers of 

 liquid will be dragged along with the charged particles. This causes 

 the rise of the liquid on the side of that electrode towards which the 

 particles move.^ 



This electric osmose gives us a chance to test our assumption that 

 the water molecules assume a different charge according to the nature 

 of the electrolyte; namely, (1) that the water molecules assume a 

 positive charge when the collodion bag is filled with solutions of neu- 

 tral salts with a monovalent or bivalent cation or with solutions of 

 hydroxides with monovalent or bivalent cations, (2) that the water 

 molecules assume a negative charge when the collodion bag is filled 

 with solutions of neutral (or acid) salts with a trivalent or tetravalent 

 cation, or with solutions of acids. 



If our assumption is correct, water should move towards the cathode 

 in the case of the electrolytes mentioned in (1) (Group A, Table V) 

 and towards the anode in the case of electrolytes mentioned in (2) 

 (Group B, Table V). This is actually the case. 



The collodion bags, closed by a perforated rubber stopper through 

 the hole of which a glass tube with a bore of 2 mm. was inserted, 



* It should be noticed that a collodion membrane belongs in all probability 

 to the type of non-porous diaphragms. 



