This term applies to chemical and isotopic  fractionation during phase transformation when one phase progressively evolves from another of limited size and is continuously removed. Upon evaporation of an alcoholic solution, ethanol concentrates into the first vapor extracts and, as a result of the finite original supply, becomes depleted in the residual liquid. Distillation, which bears the name of “Rayleigh distillation” from Lord Rayleigh who provided the original equation, greatly enhances fractionation over exchange at equilibrium. Distillation as described for spirit amounts to fractional evaporation: changing phases leads to fractional condensation (rain), fractional crystallization (magmatic differentiation), fractional melting, etc.