Distillation

If you evaporate salt water, you get the salt but lose the water. To get the liquid back, or to separate two liquids that mix completely (miscible liquids), you use distillation.

How distillation works:

• Heat the mixture in a distillation flask. The liquid with the lower boiling point turns into vapour first. A thermometer shows the temperature.
• The vapour passes into a condenser, which is kept cool by flowing water or air. The vapour cools and turns back into pure liquid.
• This pure liquid, the distillate, drips into a receiver. The rest stays behind in the flask.

Simple distillation works when the boiling points differ by at least about 25 °C. Example: acetone (boils at about 56 °C) and water (100 °C). Distillation can also take pure water out of salt water.

When the boiling points are closer than 25 °C, we use fractional distillation. In an oil refinery, crude oil is separated into:

• petroleum gas;
• petrol;
• kerosene (also aviation fuel);
• diesel;
• lubricating oil;
• bitumen (for roads).

Petroleum gas squeezed into cylinders under pressure becomes a liquid: that is your kitchen LPG.

The smell of the first rain, in a bottle. In Kannauj, India's perfume capital, craftspeople capture the earthy smell of the first rain as *Mitti ka Ittar. They use an old distillation method called Deg-Bhapka*.