Rectification is one of the most complex energy and metal-intensive chemical and technological processes that have a strong influence on the quality of commodity products, the economy and ecology of production. It is a major process in the petrochemical and oil processing industries and its main apparatuses, rectification columns, are part of common technologies that have many interrelated parameters. The current environmental problems and requirements for the quality of commodity products are increasing and call for improvement of the resolution of rectification installations through their reconstruction by modernizing the basic equipment of the columns. The efficiency of the mass exchange process on the tray is characterized by differential and integral characteristics. The differential (local) characteristic determines the mass transfer in the elementary (local) volume of the gas-liquid system, and the integral one does so on the entire tray. The local efficiency coefficient, ЕOG, (local efficiency) is used as a differential characteristic and the efficiency coefficient of the tray (Murphree efficiency) is used as an integral characteristic. The aim of the present work is to experimentally study the effects of vapour velocity and the concentration of the initial mixture on the local efficiency of rectification and foam height in a glass laboratory column with a single sieve tray.