水蒸气蒸馏Steam distillation

两种互不相溶的液体共存时，各自独立产生蒸气压，总蒸气压 p = p_水 + p_有机物。当总压等于大气压时混合物沸腾，因此沸点低于两者中任何一种的沸点（低于 100 °C）。馏出液中两组分的质量比 m_有机/m_水 = (p_有机·M_有机)/(p_水·M_水)，有机物摩尔质量大，所以即使蒸气压小，蒸出的质量也较可观。

When two immiscible liquids coexist, each exerts its own vapour pressure and the total is p = p_water + p_organic. The mixture boils when the total equals atmospheric pressure, below the boiling point of either component and so below 100 °C. The mass ratio in the distillate is m_org/m_water = (p_org·M_org)/(p_water·M_water); because the organic compound's molar mass is large, a useful mass distils even though its vapour pressure is small.

水蒸气蒸馏是提取薰衣草、玫瑰、薄荷、桉树等精油的传统方法，可追溯到 10 世纪阿拉伯学者伊本·西那用蒸馏制取玫瑰水。实验室中用于从反应混合物中分离苯胺、硝基苯、邻硝基苯酚（分子内氢键使其挥发，可与对位异构体分离）和萜类化合物。

Steam distillation is the traditional way to extract essential oils of lavender, rose, mint and eucalyptus, going back to the tenth-century Arab scholar Ibn Sina's production of rose water. In the laboratory it separates aniline, nitrobenzene, o-nitrophenol (volatile thanks to intramolecular hydrogen bonding, so it can be parted from the para isomer) and terpenes from reaction mixtures.

被蒸馏物须与水不互溶、不与水反应，在 100 °C 附近有约 1.3 kPa 以上的蒸气压。用水蒸气发生器产生蒸汽，安全管调节压力；蒸馏瓶倾斜放置以防液体溅入冷凝管；馏出液清亮无油珠时可停止。馏出液经分液、干燥得到产品。

The substance must be immiscible with and unreactive toward water and have a vapour pressure of at least about 1.3 kPa near 100 °C. A steam generator with a safety tube supplies steam; the flask is tilted to stop splashing into the condenser; distillation stops when the distillate runs clear without oil droplets, and the product is separated and dried.