Liquids can be made to boil at low temperature where they can be distilled easily. This process is called vacuum distillation.
Vacuum distillation has many advantages. It decreases time for the distillation process and is economical because less fuel is required. Many compounds can be avoided from decomposition e.g., glycerin boils at 290°C at 760 torr pressure but decomposes at this temperature. Hence glycerin cannot be distilled at 290°C. Under vacuum, the boiling temperature of glycerin decreases to 120°C at 50 torr. It is distilled at this temperature without decomposition for purification.
Food is fastly prepared in pressure cooker
We can increase the external pressure artificially on the surface of boiling water by using a pressure cooker. Pressure cooker is a closed container. The vapour of water formed are not allowed to escape. In this way, they develop more pressure in the cooker and the boiling temperature increases. As more heat is absorbed in water, so food is cooked quickly under increased pressure.
