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Azeotropic mixture

A solution of two or more liquids, the composition of which does not change upon distillation. The composition of the liquid phase at the boiling point is identical to that of the vapor in equilibrium with it, and such mixtures or azeotropes form constant-boiling solutions. The exact composition of the changes if the boiling point is altered by a change in the external pressure. A solu­tion of two components which form an azeotrope may be separated by distillation into one pure component and the azeotrope, but not into two pure components.