The persistence of the liquid state of aggregation above the critical temperature. The system ethylene

Abstract

The research described below arose from previous investigations carried out in this laboratory.* In a study of the influence of molecular compound formation on the rate of reaction (MAASS and SIVERTZ, 1925) it was found that although propylene and hydrogen chloride apparently react in a reproducible manner when the reactants are brought together in the liquid state, no measurable reaction occurs when they are brought together as gases. At first this was ascribed to the difference in concentration between the liquid and the gaseous states. However, it was shown (Sutherland and Maass, 1931) that when propylene and hydrogen chloride are brought together at room temperature as gases and heated above the critical temperatures of the mixture, no reaction occurs even when they are compressed to a concentration as great as that of the liquid mixture slightly below the critical temperature. The rate of reaction of the liquid mixture was found to increase with rise in temperature in the usual manner up to the critical temperature, but was found to be nil in the absence of the liquid phase. The acquirement of results of a similar nature by the application of the same procedure to other systems has been delayed owing to the fact that for most systems in which a homogeneous reaction takes place in the liquid state the critical temperatures and pressures are so high as to enhance greatly the experimental difficulties. An attempt to overcome these difficulties is still in progress. In the meantime other investigations have been undertaken with the object of finding a possible explanation for a discontinuity in reaction rate at the critical temperature. The first was an attempt to discover whether or not at the critical temperature a marked discontinuity of state exists in a two-component system, in contrast to the continuous change generally accepted as taking place in a one-component system.