 the binary phase-envelope diagram (boiling-point curve) must be correctly read.A mixture of 5% water with 95% tetrahydrofuran is an example of an azeotrope that can be economically separated using a pressure swing – a swing in this case between 1 atm and 8 atm.By contrast the composition of the water to ethanol azeotrope discussed earlier is not affected enough by pressure to be easily separated using pressure swings and instead, an entrainer may be added that "either" modifies the azeotropic composition and exhibits immiscibility with one of the components, "or" extractive distillation may be used.