Metamorphosis from LCEP to UCEP in the metastable three-phase region

The behavior of the phase lines in binary gas-liquid systems was classified by van Konynenburg and Scott according to the various connectivities of th e critical lines and the three-phase lines, occurring in the pressure tempe rature diagrams of such systems. The three-phase line in type IV starts at a (LL)V Feint and ends at a L(LV) point. Somewhere near this line a transit ion takes place which determines the outcome at the end of the line. At thi s changeover point, called the plait-point transformation, two binodal cusp s meet each other on the spinodal and at the same time, on the other end of the tieline, two binodals will cross each other and osculate. This phenome non is described and analyzed in detail and a mathematical description of t his behavior is given.