Consider a ternary mixture composed of water, dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF). For user-set values of the temperature, this Demonstration computes the liquid-liquid equilibrium diagram, which is classified as an island type. A few tie lines (the green line segments) are included. An island binodal curve has two plait points that limit the tie lines on each side of the island. The plait points (the red dots) are calculated.