Issues of thermodynamic theory of heterogeneous equilibrium in the application to liquid-pair systems, structure of phase equilibrium diagrams, methods of experimental study of liquid-pair equilibrium. are considered. Particular attention is paid to the possibilities of testing the thermodynamic consistency of experimental data and methods of a priori calculation of liquid-vapor equilibriums in multicomponent systems. For scientific and engineering workers of chemical, petrochemical and other industries engaged in the development and optimization of separation and purification processes . Can be useful for teachers, graduate students and students of chemical-technological universities and chemical faculties of universities . Screenshots