Distillation
an important process in the arts; consisting essentially in converting a liquid into vapor in a closed vessel, by means of heat, and then conveying the vapor into another cool vessel, where it is condensed again into a liquid. When applied to a solid the process is called sublimation. The object of distillation is to separate one substance from others with which it may be mixed. In distillation proper no chemical decomposition takes place; when any of the substances are decomposed it is called destructive distillation. Destructive distillation is the term applied to the process of heating vegetable and animal substances in retorts or similarly closed vessels at a temperature sufficient to decompose the original substance, and to obtain therefrom products possessing different properties from the material which yielded them.
Examples of this process are the heating of coal in gas-works at a red heat, when it resolves itself into coke, which is left in the retort, and coal-gas, naphtha, tar, etc., which distill over into suitable receivers.