An apparatus for the measurement of the second virial coefficients of vapours; the second virial coefficients of some n -alkanes and of some mixtures of n -alkanes

Abstract
An apparatus for the measurement of the second virial coefficients of vapours is described. It is designed so that a sample of the gas under investigation can be compared directly with a reference gas (nitrogen). This differential method has practical advantages over direct methods. The apparatus has been used to measure the second virial coefficients of the series of n-alkanes from propane to n-octane from near room temperature to about 140 $^\circ$C. The results form a family showing deviations from the principle of corresponding states which increase regularly with increasing chain length. A simple formula based on the principle of corresponding states has been found to fit not only the present measurements, but also, previous measurements by other workers at higher temperatures on these substances, and also previous measurements on methane and on ethane. Measurements have also been made on equimolar mixtures of propane+n-heptane and of propane+n-octane. The results are in much better agreement with a slight extension of a rule of Guggenheim & McGlashan (1951) based on the principle of corresponding states than with the rule of Lewis & Randall (1923).