Points in Electrolysis. 7 



From the definition of electromotive force adopted in this 

 paper, the " seat of the electromotive force " is in the cell 

 and not between the positive and negative metals outside. 

 Yet the electrometer behaves as if there were a contact elec- 

 tromotive force. Dr. Lodge has attempted to explain this in 

 accordance with the a chemical theory." He argues that 

 when, for instance, zinc is exposed to the air, the oxygen 

 either begins to combine with it, or actually combines with it, 

 the particles of oxygen giving up their charge to the zinc on 

 combining. This produces a difference of potential which 

 increases till the oxygen's attraction for the zinc is counter- 

 balanced by it. There is thus an electromotive force set up. 

 Air being an insulator, the circuit is not completed. If the 

 tendency to combine with oxygen can produce an electric 

 stress which prevents combination, actual combination must 

 either charge the metal, if insulated, or produce a current, if a 

 path is allowed. If a clean piece of sodium is put on an 

 insulating stand it goes on oxidizing, the amount of oxide 

 formed corresponding to an enormous number of coulombs. 

 Where do they go to ? If the metal charges electrostatically, 

 it must soon be millions and millions of volts below the 

 potential of the air, and must discharge disruptively. More- 

 over, the millions of volts are far more than equivalent to 

 Na 2 ,0. Dr. Lodge assumes that a single element is an 

 electrolyte, whereas a cell can only discharge by double de- 

 composition. That is to say, to produce such an effect the metal 

 must tear the oxygen from a combination, the other radical 

 combining with another less electropositive metal, or remov- 

 ing an electronegative radical from it. It might be argued 

 that zinc and copper plates in chlorine water will give a 

 current, and chlorine is a single radical like oxygen. But 

 immediately the plates are inserted the chlorine combines 

 directly with both metals, without giving any current. A 

 three-fluid battery is thus produced. The zinc is in a solution 

 of zinc chloride, and the copper in copper chloride, and the 

 intermediate liquid is chlorine water. The cell then dis- 

 charges like a Daniell. 



Though the oxygen form of the corrosion theory of contact 

 electromotive force may not hold, it is quite possible that the 

 Volta effect may be produced by thin films of water. Water 

 is even more difficult to get rid of than oxygen, and might 

 easily cause the electrometer readings. It must be remem- 

 bered in connexion with this, that water must be present to 

 enable even a combination of a metal with chlorine to take 

 place. It is well known that dry chlorine will not attack a 

 dry metal. Even sodium may be left in contact with chlorine. 



