What is fractional distillation?

Fractional distillation is the separation of mixtures of liquids even if their boiling points are similar. The mixture is heated in a flask with a fractioning column at the top. The liquid with the lowest boiling point evaporates first and will reach the top of the column. Liquids with higher boiling points may also evaporate, but the column is cooler towards the top, so the condense and run backdown into the flask. When the first liquid has been collected, you raise the temperature.