A laboratory from 1580. In chemistry, distillation means the separating of the constituents of a liquid by boiling it and then condensing the vapor that results. Distillation can be used to purify water or other substances, or to remove one component from a complex mixture, as when gasoline is distilled from crude oil or alcohol from a mash. When water is purified by distillation, it is boiled in a container, and the steam is sent into cooling tubes. The steam is condensed and then collected as purified water in a second container. The impurities in the water are left behind in the first container and can be discarded.