Four equally-spaced electrical-resistivity probes are placed on opposite sides of the sample. A current is flowed through the outer probes, and the potential is measured between the inner probes at specified times. The direction of current flow is reversed after each reading to reduce the impact of ion concentrations. The electrical-resistivity setup presently being constructed is similar to typical four-point measurements that are performed for geological applications (Chaker, 1996). The measured resistivities are more accurate than those determined with our initial across-the-test-specimen, two-point measurements which were used to map the location of gas hydrate within the test specimen (Booth et al, 1999).
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