蒸馏Distillation

液体的蒸气压随温度升高而增大，当蒸气压等于外界压力时沸腾。对于理想混合物，按拉乌尔定律，蒸气中易挥发组分的摩尔分数高于液相，冷凝后馏出液中易挥发组分得到富集。一次汽化-冷凝相当于一块“理论塔板”，所以简单蒸馏分离效果有限。形成共沸物的混合物（如 95.6% 乙醇-水）无法用普通蒸馏完全分离。

Vapour pressure rises with temperature, and a liquid boils when it equals the external pressure. For an ideal mixture, by Raoult's law, the vapour is richer in the more volatile component than the liquid, so the condensed distillate is enriched in it. One vaporisation–condensation equals one theoretical plate, so simple distillation separates only modestly. Mixtures that form azeotropes, such as 95.6% ethanol–water, cannot be fully separated by ordinary distillation.

装置包括蒸馏烧瓶、蒸馏头、温度计、直形冷凝管、接液管和接收瓶。液体量不超过烧瓶容积的 2/3、不少于 1/3；加沸石或磁子防止暴沸；温度计水银球上缘与蒸馏头支管下缘平齐，以准确测量蒸气温度；冷凝水下进上出；不能蒸干，以防过热和过氧化物爆炸。

The set-up has a distillation flask, still head, thermometer, straight (Liebig) condenser, adapter and receiver. Fill the flask between one-third and two-thirds; add boiling chips or a stir bar to prevent bumping; set the top of the thermometer bulb level with the bottom of the side arm to read the vapour temperature; run cooling water in at the bottom and out at the top; and never distil to dryness, to avoid overheating and peroxide explosions.

古希腊和古埃及已用简单蒸馏制香精和净化水。公元 8–9 世纪阿拉伯炼金术士发展了蒸馏器（alembic），用于制取酒精和精油。中国元代已有蒸馏白酒的记载。今天蒸馏是实验室最常用的提纯方法，在工业上用于石油炼制、酒精生产、海水淡化和空气分离。

Ancient Greeks and Egyptians used simple distillation for perfumes and to purify water. Arab alchemists of the eighth and ninth centuries developed the alembic for making alcohol and essential oils, and distilled spirits are recorded in Yuan-dynasty China. Today distillation is the commonest laboratory purification and is used industrially in oil refining, alcohol production, desalination and air separation.