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Inconsistencies among existing equation-of-state data for «-alkanes have been resolved by careful determinations of thermal expansion coefficients, a, and thermal pressure coefficients, y, for hydrocarbons H(CH2)"H with « = 6, 8,16, 22, 36, and =°( linear polymethylene) over ranges of temperature and at zero pressure. These experimental results in conjunction with selected data from the literature for other hydrocarbons are compared with the reduced equation of state specified by the partition function proposed recently (Flory, Orwoll, and Vrij) for chain molecule liquids. Excellent correlations over the entire range « = 6to °°are obtained using the same set of parameters for all homologs. Isotherms are well reproduced, but parameters of the reduced equation of state change somewhat with temperature, as previously noted. These results provide a basis for interpreting the thermodynamic properties of «-alkane mixtures.A partition function, which is of such simplicity as to permit its ready application to liquids and liquid mixtures consisting of nonspherical molecules, has been formulated recently for the express purpose of comprehending those equilibrium properties of mixtures which elude conventional theories.1-3 Analysis of thermodynamic data for mixtures of small molecules met with encouraging success, particularly with respect to the correlation of excess volumes and excess enthalpies. 4The similar treatment of polymer solutions promises to resolve long-standing discrepancies between theory and experiment.5The partition function and the equation of state derived from it are adaptable also to the representation of homologous chain molecules. A previous attempt1 to apply the theory to «-alkanes ranging from «-hexane to polymethylene was hampered by inadequate accuracy of some of the existing equation-of-state data. Reliable values for the thermal pressure coefficients, y = (dp/ dT)v, have been determined for only a few of the homologs; even the thermal expansion coefficients, a = (\/V)(dV/dT)P, are not known with sufficient accuracy in some instances.We have accordingly undertaken to determine a and 7 for five «-alkanes and for linear polymethylene. The results of these measurements are here presented and compared with selected data from the literature for these hydrocarbons and other homologs. The equation-of-state parameters for this important homologous series of chain molecules are correlated with the theory cited above. Experimental Section«-Hexane and «-Octane. Chromatoquality grade «-CsH» and «-CgHis, purchased from Matheson Coleman and Bell, were used without further purification. According to gas chromatographic analyses by the supplier, the former contained 0.5 mole % of methylcyclopentane and 0.08 mole % of methylpentane, and the latter about 0.3 mole % of unspecified impurities.Thermal expansion coefficients of «-CeHn and «-CsHi8 were measured using the Pyrex dilatometer represented in Figure 1.

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