โ Scribed by Anders Wikby; Gillis Johansson
No coin nor oath required. For personal study only.
As part of a programme to study the properties of glass electrodes we have reinvestigated the resistances measured with direct current and with alternating current. Such measurements should provide information about the solid state side of the glass-solution interface. We hoped originally that changes in solution would affect the resistance, at least to some small extent. This was not the case, but instead a quite unexpected energy barrier appeared in the surface.
Earlier measurements of the resistance provided a check on the usefulness of the glass composition 1. Too high resistances resulted in slow response or current leaks in the electrometer connections. Both d.c. 2 and a.c. 3 were used and it was observed that a.c. measurements gave a much lower value. The high d.c.-value was attributed to a back e.m.f., but it was nevertheless concluded that the relevant quantity for a glass electrode was the d.c.-value. These experiments are reviewed in Dole's classical monograph 4. The existence of an internal e.m.f, was later rejected. Since the d.c. resistance obeys Ohm's law Eckfeldt and Perley s collected evidence to dismiss the polarization theory. They showed that much of the discrepancy between the a.c. and d.c. measurements could be explained by treating the glass as a dielectric. Distrche and Dubuisson 6 used a pulse technique to obtain an equivalent circuit for the glass electrode. The values obtained were quite different from those obtained by measurements with d.c. and the differences could not be explained by the authors. The present work shows that they used an over-simplified equivalent circuit and that the contributions from cable and electrometer capacitances may be in error. Impedance measurements seemed to provide very little information about the electrode properties and therefore few investigations were made between the thirties and the present time.
During recent years glass electrodes selective to cations other than hydrogen have been investigated in several reports. Eisenman 7 has edited a monograph on the subject. He and his co-workers 8 have determined the current-voltage relations of some membranes in this respect. Buck 9'1ยฐ and Buck and Krull ~1 have recently measured the d.c. and a.c. resistances of glass electrodes with modern equipment. By using the Cole-Cole plot they were able to distinguish a surface impedance on their porous electrodes. They did not observe it on other electrodes, probably owing to the high total resistances of these.
The electrical properties of glasses not specifically designed for electrode purposes have been studied extensively and reviewed in several monographs, e.g. by Morey 12. Some Russian investigations have been briefly reported in the papers
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This surface resistance has been measured normal to the electrode surface. The resistance has been found to be located some distance within the physical surface and the name surface should therefore not be interpreted too literally.
This surface resistance has been measured normal to the electrode surface. The resistance has been found to be located some distance within the physical surface and the name surface should therefore not be interpreted too literally.
The glass electrode is calibrated on the concentration scale against the hydrogen electrode from measurements of the potentials of the two electrodes immersed in the same buffer. The p[H+] of the buffer is changed between 2 and 11 by addition of base. The difference in potential between the electrod