Viscosities of liquids at constant volume

Abstract

The design and construction of a falling-cylinder viscometer for use at pressures up to 3000 atm. are described. The instrument has been employed for the first direct measurement of the variation of the viscosity of a liquid with temperature at a constant volume which is determined by the density of the liquid at the temperature at which the high-pressure vessel is filled and sealed. Preliminary measurements are reported on benzene and carbon tetra-chloride. The results have confirmed experimentally the straight-line relation between log η and 1/ T at constant volume as predicted in the viscosity theories of Andrade (1934 a , b ) and Eyring, Glasstone & Laidler (1941, chap. IX). Further confirmation has been obtained by combining some recent atmospheric pressure viscosity measurements at very low temperatures (Giller & Drickamer 1949) with existing high-pressure and compressibility data. E v , the energy of activation of viscous flow at constant volume, has been calculated over a wide volume range and its importance is discussed. For many simple organic liquids, there appears to be a simple general relation between E v and volume. E v is considered to be the ‘true’ activation energy of viscous flow and its relation to E vis , the quantity usually described as the activation energy of viscous flow, calculated from the variation of the viscosity with temperature at constant (atmospheric) pressure, is discussed.