Electrolytic separation of metals with controlled cathode potential

The ideal deposit for analytical purposes is adherent, dense, and smooth in this form it is readily washed without loss. Flaky, spongy, powdery, or granular deposits adhere only loosely to the electrode, and for this and other reasons should be avoided. 

The nitrate ion is reduced to ammonium ion at a lower (i.e. less negative) cathode potential than that at which hydrogen ion is discharged, and, therefore, acts to decrease hydrogen evolution. The nitrate ion acts as a cathodic depolariser. 

Raising the temperature, say to between 70 and 80 °C, often improves the physical properties of the deposit. This is due to several factors, which include the decrease in resistance of the solution, increased rate of stirring and of diffusion. 

6 ELECTROLYTIC SEPARATION OF METALS WITH CONTROLLED CATHODE POTENTIAL 

In the common method of electro-gravimetric analysis, a potential slightly in excess of the decomposition potential of the electrolyte under investigation is applied, and the electrolysis allowed to proceed without further attention, except perhaps occasionally to increase the applied potential to keep the current at approximately the same value. This procedure, termed constant-current electrolysis, is (as explained in Section 12.4) of limited value for the separation of mixtures of metallic ions. The separation of the components of a mixture where the decomposition potentials are not widely separated may be effected by the application of controlled cathode potential electrolysis. An auxiliary standard electrode (which may be a saturated calomel electrode with the tip of the salt bridge very close to the cathode or working electrode) is inserted in the 

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