AbstractAn Oldershaw column has been operated with two negative systems; ethylene dichloride/toluene, and ethylene dichloride/224 trimethylpentane. The difference in surface tension between ethylene dichloride and toluene at 90°C. is about one‐seventh of the difference between ethylene dichloride and 224 trimethylpentane at the same temperature. It is shown that this surface tension difference does not significantly effect the overall performance of a perforated plate column. Photographs taken show no apparent change in foam structure for the two systems at all boil up rates.Vapor‐liquid equilibrium data has been determined for the system ethylene dichloride/224 trimethylpentane at 750 mm. mercury pressure. There is an azeotrope of composition, 77.0 mole % ethylene dichlo