Electrolysis, the nature of electrolytic conductance, ions

7 ELECTROLYSIS, THE NATURE OF ELECTROLYTIC CONDUCTANCE, IONS Chemically pure water practically does not conduct electricity, if however, as already stated, acids, bases, or salts are dissolved in it, the resultant solution not only conducts the electric current, but undergoes chemical changes as well. The whole process is called electrolysis. 

Phenomena occurring during electrolysis can be studied in the electrolysis cell shown in Fig. 1.1. The electrolyte solution is placed in a vessel, into which 

The chemical change occurring during the course of electrolysis is observable on or in the vicinity of the electrodes. In many cases such a change is a simple decomposition. If for example a dilute solution of hydrochloric acid is electrolysed (between platinum electrodes), hydrogen gas is liberated on the cathode and chlorine on the anode the concentration of hydrochloric acid in the solution decreases. 

It is easy to demonstrate that electrolysis is always accompanied by the transport of material in an electrolysis cell. If for example the blue solution of copper sulphate and the orange solution of potassium dichromate are mixed in equimolar concentrations, a brownish solution is obtained. This solution can be placed in a U-shaped electrolysis cell and topped up with a colourless layer of dilute sulphuric acid on each side (Fig. 1.2). If this solution is then electrolysed, the hitherto colourless solution next to the cathode slowly becomes blue, while 

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