Which liquid distills first when two liquids have different boiling points?

When heating a mixture of substances, the most volatile component—which is the liquid with the lowest boiling point—distills first.1

In the process of distillation, the vapor above a liquid mixture contains a higher proportion of the more volatile substance. As the mixture is heated, this substance vaporizes more readily, allowing it to be collected as a distillate while the less volatile components remain or distill later. For mixtures where boiling points are close together, techniques such as fractional distillation are used to enhance this separation by repeatedly condensing and revaporizing the vapors to ensure the most volatile component is isolated.12