The influence of pressure on the equilibrium between carbon dioxide and air

The equilibrium between solid carbon dioxide and air has been examined at pressures from atmospheric to 200 atm and at temperatures from ─110 to ─196° C. At the lower temperatures and higher pressures within this range the air was condensed to the liquid state. The concentration of carbon dioxide in the mixed phase, particularly at high pressures and the lowest temperatures, was found to be many times greater than would be expected from Dalton’s law, even when modified by Poynting’s relation for the effect of the compressed gas phase. Under extreme conditions the deviation was more than a thousandfold. The behaviour of this system is shown, by general phase-rule considerations, to be consistent with that of a binary system in the neighbourhood of the critical point of the more volatile component when the second component separates as the solid phase.