Viscosity of liquid sodium and potassium

Abstract

According to the theory of liquid viscosity put forward by Professor Andrade, the viscosity of a liquid is closely connected with the characteristic frequency of vibration, and the temperature coefficient of viscosity obeys an exponential formula involving an internal energy coefficient. It appears that, for comparison with theory, viscosity data for elementary substances like liquid metals are specially desirable. Hitherto, viscosity measurements have been largely confined to organic liquids, while for liquid metals, with certain notable exceptions, viscosity data have been scanty and discrepant. The work described below was undertaken with the view of supplying some of the data which are needed. Sodium and potassium were chosen for the measurement on account of the simplicity of both their atomic structures and of their crystal form. They also have the advantage that the viscosities of the other three alkali metals—lithium, rubidium, and caesium—are also accessible to measurement, the melting points lying within an easily-realized temperature range. Owing to the fact that these metals oxidize very quickly in the presence of even a slight trace of air, the sphere method, in which the liquid is enclosed in a sphere and its viscosity found by observing the damping of the oscillations about a vertical axis, is specially suitable for the purpose. This method, as lately developed by Professor Andrade and the author, has proved capable of an accuracy probably as great as that of the standard methods. It is simple in manipulation, renders temperature control easy, and does not involve the corrections involved in capillary tube methods.