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On the basis of new experimental PVT data and of selected literature values, this paper derives a Martin-Hou equation of state which correlates, within i=O.18% standard deviation, data in the experimental ranges of 25-130°, 10-75 bars, and 1.05-13 cc/g. A vapor pressure equation with six constants describes the data within =t0.18% standard deviation between -45 and +45.64", the critical temperature. A density equation with five constants correlates data between -41 and +42" with a per cent standard deviation of =tO.lO'%. The Martin-Hou equation serves to compute virial coefficients and a variance-covariance matrix treatment indicates their probable accuracy.

0.80 mole fraction. I n this high concentration range of gaseous methane, the molar volume of the gas mixture is linear in mole fraction, and therefore, the partial molar volume of methane in the gas is trivially different from the molar volume of pure gaseous methane.

The slopes of isochors and isotherms as they cross the unit compressibility line are found to constitute a corresponding property for many fluids over a wide range of densities extending from dilute gases to compressed liquids. This correspondence is represented by a simple function, and its consequences for equations of state are examined. In particular, a new interrelation among the virial coefficients is derived. The interrelation is tested for the Lennard-Jones 12,6 intermolecular potential, and the agreement permits an estimation of this potential's previously unknown sixth virial coefficient as a function of temperature.