Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

2 THE SOLIPGAS INTERFACE 205or an evaporated metal film'28 on the wall of the cell. The electrode arrangementused in these experiments is shown diagrammatically in Fig. 13.(e) The contact potentialIf two metals of differing work function are connected electrically, at the sametemperature and without a source of emf, the electrostatic potentials just outsidethe two surfaces are different. This potential difference V,, is known as the contactpotential difference and is equal to the difference in the work functions of the twometals 4, and 4,. If a compensating potential, equal and opposite, is appliedacross the plates, the field becomes zero.The two metals act as the plates of a condenser, one of the plates being usedfor adsorption of the gas and the other being a reference electrode. Adsorptionof gas causes a change in contact potential equal to the change in work function.Disappearance of the electrical field between the two plates may be detected eitherby the steady condenser methodx3' or the vibrating condenser method'3'*'32.A glass adsorption cell used for the static condenser method is shown in Fig. 14.The condenser is formed from two concentric cylinders separated by a 2 mm gap.IFig. 14. Cell for the measurement of contact potential difference by the static condenser method.From ref. 130.References pp. 270-278