In pre-modern chemistry

Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 and alchemy

Alchemy

Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...

, cohobation was the process of repeated distillation

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 of the same matter, with the liquid drawn from it; that liquid being poured again and again upon the matter left at the bottom of the vessel.

Cohobation is a kind of circulation

Circulation

Circulation may refer to:*Circulatory system, a biological organ system whose primary function is to move substances to and from cells*Circulation , the path integral of the fluid velocity around a closed curve...

, only differing from it in this, that the liquid is drawn off in cohobation, as in common distillation, and thrown back again; whereas in circulation, it rises and falls in the same vessel, without ever being drawn out.