At low frequencies, the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization. This problem at the electrode-sample interface arises from the modulation of the normal dc boundary potential by the passage of alternating current. A solution, permitting a conductance resolution of 1:105 for frequencies between 10 cps and 1 kc, is to use a second noncurrent-carrying pair of electrodes to measure the voltage across the sample and to employ a null technique for obtaining the required precision. Several four-electrode null techniques are proposed, each having certain relative merits. In all cases the resolution in capacitance is shown to be governed by a combination of the resolution in conductance, the sample properties, and the frequency of the measurement.

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