Viscosity–Volume Relation for Liquids

Abstract

DR. JOBLING, in his letter published in Nature of October 16, states that the dependence of the viscosity of a liquid on temperature is "certainly for ether above 0° C. and probably for many other liquids" due entirely to the change of volume. That this is not so in general has often been pointed out by one of the present writers¹. For example, for mercury (a monatomic liquid and so more suitable than ether to be cited in support of a theory of liquid viscosity) the temperature variation of viscosity at constant pressure in the range 30–75° C. is reduced only by some thirty per cent when the volume, instead of the pressure, is kept constant² ; for isoamyl alcohol, working at constant volume reduces the temperature variation by some twenty-two per cent only : nowhere in the whole range of recorded experiments on carbon dioxide is the viscosity a function of the specific volume alone. Dr. Jobling also states that on Born and Green‘s theory the part of the viscosity that depends upon molecular attraction is a "volume effect" : this, however, is not proved, or even asserted, by the authority quoted by him, and is certainly not asserted or implied by Born and Green³. The only experimental results that Dr. Jobling brings forward to support his contention refer to ether above 0° C. However, even for ether in the temperature-range considered, from 0° to 32°, the evidence fails.