the apparatus for phase equilibrium data determi-nation has been developed of water-salt system at high temperature. A five-component system NaOH-Na2CO3-Na2SO4-NaCl-H2O was studied at 150℃. The work completed the phase equilibrium investigation for the system at 150℃. On the basis of the phase equilibrium data obtained present and those available in literature
the phase diagrams were plotted for the NaOH-Na2CO3-Na2SO4-NaCl-H2O five component system at 150℃. According to the phase diagrams
the author made phase diagram calculation for the evaporation process in manufacturing caustic soda from natural soda in Inner Mongolia by caustic method.