An azeotrope (pronounced /ay-ZEE-ə-trope/)'s a mixture of two or more liquids (chemicals) in such a ratio that its composition can't be changed by simple distillation. This occurs because, when an azeotrope's boiled, the resulting vapor has the same ratio of constituents as the original mixture. Because their composition's unchanged by distillation, azeotropes are also called (especially in older texts) constant boiling mixtures. The word azeotrope's derived from the Greek words ζ^… (More on Azeotrope)