Manchester Memoirs, Vol. Ixl. (191 7) No. 9 19 



If iron, nickel and cobalt ions are hydrated in the same 

 w,ay as hyldrion, their high overvoltages are readily understood. 

 Since the process of hydr,ation takes place automatically, work 

 must I'be done in the dehydration of these ions. Hence a resisting 

 force will be produced tending to prevent the separation of these 

 ions, which \vill increase with increasing current density. If a non- 

 hydrated ion such as, zinc ion be present in an acid solution, this 

 ion will not he subject to the resisting force, and at high current 

 densities will separate in much greater quantity than the, hydrogen 

 ion, in spite of the lower potential necessary to separate the 

 latter. 



If, however, a hydrated ion such as ferrous-ion be present, 

 this will be subject to a similar resisting force to that opposing 

 the hydrion, with the result that both will deposit together in 

 an ideal condition for hydride formation. 



If an acid solution containing zinc and iron sulphates is sub- 

 jected to a high current density, zinc will deposit readily. Iron 

 and hydrogen will deposit in much smaller quantity, and some 

 of these will re- enter the solution in the form of iron-hydride-ion, 

 which having a high solution potential will readily reduce zinc 

 out of the solution. As a result nearly pure zinc may be 

 deposited from a very impure electrolyte, and this process is 

 being worked on the large scalei in South Africa', with consider- 

 able success. It is evident th!at the method may also be applied 

 in the separation of many other metals from iron, nickel and 

 cobalt. 



The single potentials of these three metals in contact with 

 solutions containing the same ions are greatly altered by stirring 

 the liquid or moving the metal in the electrolyte. When the 

 inetal is first placed in the liquid, hydrated ions deposit on the 

 metal, discharge and lose their water of hydration. At the same 

 time, non-hydrated ions will be thrown off, and will hydrate before 

 returning. The speed of the returning ions is therefore much 

 less than that of the outgoing ions, and when equilibrium i? 

 established, the potential of the electrode will be greatly lowered 

 by this action. On rapidly moving the electrode, the speed of 

 the incoming ions is increased, while that of the outgoing ions 

 is 'almost unaltered, with the result that in some cases the poten- 

 tial rises by over o.i volt. j 



A copper plate treated in the same way shows a barely 

 detectable rise of 0.002 volt. 



This behaviour again supports the proposition that the ions 

 of iron, nickel and cobalt are hydrated. 



Further, it has been found that colloids are carried into the 

 electrode surfaces only by hydrated ions. In this way it ha? 

 been shown that the hydroxyl ion is also hydrated. 



