Steam Distillation

Steam distillation is applicable to both solid and liquid organic compounds, but only under a specific set of conditions: the compound must not decompose at the temperature of steam, it must have a fairly high vapour pressure at 373 K (the boiling point of water), it must be essentially insoluble in water, and any impurities present alongside it must themselves be non-volatile. Where those conditions hold, the technique lets a compound be distilled and purified at a temperature well BELOW its own normal boiling point, which is exactly what makes it valuable for heat-sensitive substances.

Practically, the impure liquid, together with a little water, is placed in a round-bottom flask that is connected on one side to a steam boiler and on the other to a water condenser, and the flask itself is kept tilted at a slight angle so that no droplets of the boiling liquid mixture can splash directly into the condenser. As the flask contents are heated and a brisk current of steam is passed through, the compound's own vapour mixes with the steam and is carried, together with it, into the condenser; the resulting condensate -- a mixture of water and the organic compound -- is then simply separated (the compound typically being immiscible with, and less dense or denser than, the water). Steam distillation is the standard industrial method for recovering essential oils from plants and flowers, and it is also used in manufacturing aniline and turpentine oil. A classic textbook application is separati …