For example, acetone / methanol / chloroform form an intermediate boiling (saddle) azeotrope. Formic acid forms a low-boiling azeotrope with water (22.4%). The best known example is adding benzene or cyclohexane to the water/ethanol azeotrope. The resulting ternary azeotrope is neither positive nor negative. This page contains tables of azeotrope data for various binary and ternary mixtures of solvents. This lower-boiling ternary azeotrope is removed preferentially, leading to water-free ethanol. Like benzene, thiophene forms an azeotrope with ethanol. Another method, pressure-swing distillation, relies on the fact that an azeotrope is pressure dependent. The result is that the distillate is richer in chloroform than the original azeotrope. An example is acetic acid and water, which do not form an azeotrope. Each azeotrope has a characteristic boiling point. However, the formation of an azeotrope is not necessary for steam distillation to work. For example, benzene and hexafluorobenzene form a double binary azeotrope. A more extreme example is the azeotrope of 1.2% water with 98.8% diethyl ether. There are two types of azeotropes&colon; minimum boiling azeotrope and maximum boiling azeotrope.