The effect of capillary constraints on the electrical resistivity of sodium and potassium

Measurements of the electrical resistivities of unconfined specimens of sodium and potassium give values which are systematically lower than those obtained from capillary specimens. We show that this difference arises simply from the difference in thermal expansion between the materials of the capillary specimen and the capillary tube. Our results indicate that negative pressures of up to about 2000 atmospheres can exist in capillary specimens, and we conclude that capillary specimens are not suitable for precise work.