The critical compressibility factor has been used as a criterion for the correlation of the P.V.T.-behavior in the gaseous and liquid states for the diatomic gases, nitrogen, oxygen, carbon monoxide, nitric oxide, chlorine, and hydrogen chloride. Reduced densities for these substances have been calculated from available literature data. These are presented as functions of reduced temperature and reduced pressure to produce extensive density correlations for nitrogen, oxygen, and carbon monoxide. These correlations exhibit similar behavior as expected from their similar critical compressibility factors.
The validity of the critical compressibility factor as a correlating parameter has been verified by the favorable comparison of the P.V.T.-behavior of substances other than diatomic gases including argon, krypton, xenon, and methane. These results indicate that the P.V.T.-behavior of substances having critical compressibility factors of approximately 0.291 can be predicted from the reduced state correlation developed in this study as long as polarity effects are absent.