To separate two or more liquids by simple distillation, they are first heated in a flask. The more volatile liquid (the liquid with the lower boiling point) will typically evaporate first, and the vapor will pass into a condensing column, where it can revert into a liquid (condense) on the cool glass walls and then drip into a collection vessel.

In fractional distillation, a mixture of liquids is boiled and the resulting vapors travel up a glass tube called a "fractionating column" and separate. The fractionating column is usually filled with glass or plastic beads, which improves the separation between the liquids being distilled. Fractional distillation leads to a better separation than simple distillation because the glass beads in the fractionating column provide 'theoretical plates' on which the vapors can condense, reevaporate, and then recondense, essentially distilling the mixture over and over.