This Demonstration plots the residue curve of a non-ideal ternary mixture composed of chloroform, acetone, and methanol. The total pressure is 101.325 kPa. There exist three binary azeotropes and a ternary azeotrope, marked in the ternary diagram by , = 1 to 4. The residue curve map for this ternary system presents four distillation regions. Methanol and the binary azeotrope between chloroform and acetone (66.13% mole fraction chloroform) are two stable nodes. Chloroform, acetone, and the ternary azeotrope (22.90% mole fraction chloroform and 33.21% mole fraction acetone) are three saddle points. The two azeotropes, between methanol and chloroform (65.62% mole fraction chloroform) and between acetone and chloroform (79.07% mole fraction of acetone), are two unstable nodes. Drag the locator and the Demonstration plots the residue curve passing through the locator position. Such computations are useful for the determination of azeotropes, which appear as extremum points (saddle points and stable or unstable nodes).