Distillation (distillation) is the process of cleaning liquids and separating their mixtures into individual liquids by partial evaporation and subsequent condensation of the formed vapor. The liquid is heated in the flask (distillation tank) to the boiling point, the vapor is passed through a refrigerator, where they thicken, forming a distillate purified from impurities (for example, distilled water). Fractional or fractional distillation serves to separate liquids boiling at different temperatures. As the boiling point of the mixture increases, the receiver is changed and a number of distillate fractions are obtained. Re-distillation for better purification is called rectification. By distillation, it is impossible to separate azeotropic mixtures of liquids, i.e. mixtures of liquids that boil at a given external pressure at a constant temperature without changing the composition. An example of such a mixture is a 96% aqueous solution of ethyl alcohol , which boils at t ° 78.17 °. Distillation in vacuum at low temperature is used to produce substances that decompose at high temperature (for example, lactic acid). Distillation with water vapor is used to separate substances that volatilize together with water vapor from non-volatile substances (secretion of essential oils).