The working electrode preparation and cleaning

Working electrodes are normally solid. The mercury electrode is the only liquid electrode at room temperature (with the rare exceptions of gallium and amalgam electrodes) and has been most used as a dropping electrode. 

For reasons of ease of manufacture, the majority of solid electrodes have a circular or rectangular form. External links are through a conducting epoxy resin either to a wire or to a solid rod of a metal such as brass, and the whole assembly is introduced by mechanical pressure into an insulating plastic sheath (Kel-F, Teflon, Delrin, perspex, etc.) or covered with epoxy resin. It is very important to ensure that there are no crevices between electrode and sheath where solution can enter and cause corrosion. Examples of electrodes constructed by this process will be shown in Chapter 8. 

Unfortunately, expansion coefficients of plastics and metals can be quite different. For this reason it is suggested that electrodes are kept in closed glass tubes in a thermostat bath when not in use, at the temperature at which they will be employed. If this is not done, there is a 

When carbon paste is used as electrode material an electrode body is made with a shallow hole where the paste is inserted. This electrode cannot be polished when necessary the electrode is renewed. If it is a mixture of carbon paste with a plastic then careful polishing or surface cutting can be done. 

Finally, it should be emphasized that the surface of a solid electrode is not truly clean after polishing. Particles of abrasive will be stuck in the pores of the electrode, and so on. In some experiments this can make a lot of difference. For this reason it is necessary to resort to methods such as ultrasound or electrochemical cleaning the latter consists of applying different potentials or currents during predetermined periods of time to oxidize or reduce the impurities so that they leave the surface (see Ref. 15). At the same time there may be changes in surface properties (Section 3.5). 

---