Gas-liquid equilibrium compesitions for the O2-CO2 system were determined for the -49.4°C isotherm over the complete pressure range from the vapor pressure of CO2 at -49.4°C, 6.92 atm abs, to the maximum pressure of the system, 142.4 atm abs. Activity coefficients are calculated, and a thermodynamic consistency test is applied.The gas-liquid equilibrium of the O2-CO2 system at low temperatures has been studied in detail previously (2, 4> ¿0-Partly to verify and partly to complete the previous work(2) where the high-pressure range of the isotherm is missing, a series of gas-and liquid-phase equilibrium compositions were determined at -49.4°C for pressure up to the maximum, 142.4 atm abs. Activity coefficients based on the unsymmetric nor-1 To whom correspondence should be addressed. malization are calculated, and a thermodynamic consistency test is performed. EXPERIMENTALThe apparatus used here is of the vapor-recirculation type and is discussed in detail elsewhere (1). The central unit of the vapor-recirculation apparatus is the cell containing a sta-

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carbons are surrounded by -bonding rather than s-bonding electrons which characterize saturated hydrocarbons. ConclusionThe data presented here may be useful for engineering design where higher temperatures are increasingly encountered. Further, these data contribute toward the experimental information required to construct a successful theory of gas solubility. Appendix I. Minimum Cell Volume Error AnalysisSince some high-boiling solvents are costly, it is desirable to use a small solubility cell. Therefore, it is important to determine how small the solubility cell can be made without a large increase in experimental error. Further, some gases of scientific and industrial interest, e.g., hydrogen sulfide, are extremely toxic making it advisable to use as small an amount as possible.The error in Henry's constants was calculated as a function of liquid cell volume for a typical case and for the worst case with respect to pairs of gases and high-boiling solvents. The worst case is for a very slightly soluble gas, e.g., hydrogen, in a solvent with high vapor pressure, e.g., octamethylcyclotetrasiloxane.The typical case is for the squalane-ethane system. Results are presented in Figure A1. From these results it was decided that, for expensive solvents and/or toxic solutes, we may use a new, interchangeable solubility cell with a liquid volume of between 30 and 40 cm3. The cell used in previous work has a volume of 300 cm3.