The apparatus was described earlier1. The equilibrium cell was a Jerguson gauge of stainless steel with glass windows having an internal volume of 90 ml. Equilibrium was achieved by means of a gas recirculation pump. Samples of each phase were analyzed by means of a Shimadzu GC equipped with a peak integrator and a Porapack Q column. The concentrations of water vapor in the ethene were so low that they could not be detected.At low temperatures (less than 11 °C) and high pressures (greater than 11.6 atm) ethylene hydrates were observed to form.