焰色反应Flame test

在火焰高温下，金属化合物解离出金属原子，外层电子吸收能量跃迁到激发态，回到较低能级时以特定波长的光释放能量。不同元素能级不同，发射光的颜色不同：锂紫红（670.8 nm）、钠黄（589.0/589.6 nm，D 线）、钾浅紫（766.5 nm，需透过蓝色钴玻璃滤去钠的黄光观察）、钙砖红、锶洋红、钡黄绿、铜绿色（含卤素时蓝绿）、铷紫红、铯蓝紫。

In the hot flame, metal compounds dissociate into atoms whose outer electrons are excited and emit light of specific wavelengths as they return to lower levels. Each element has its own levels and so its own colour: lithium crimson (670.8 nm), sodium yellow (589.0/589.6 nm, the D lines), potassium lilac (766.5 nm, viewed through blue cobalt glass to remove sodium's yellow), calcium brick red, strontium crimson-red, barium yellow-green, copper green (blue-green with halides), rubidium red-violet and caesium blue-violet.

用铂丝（或镍铬丝）蘸浓盐酸后在火焰上灼烧至无色（除去杂质），然后蘸取待测样品在无色火焰（本生灯氧化焰）外焰中灼烧，观察火焰颜色。盐酸使金属转化为挥发性较好的氯化物。钠的焰色极强且普遍存在，微量钠就会干扰其他元素的观察。

Dip a platinum or nichrome wire in concentrated hydrochloric acid and heat it in the flame until it gives no colour, then dip it in the sample and hold it in the outer, oxidising part of a colourless Bunsen flame and note the colour. Hydrochloric acid converts metals to more volatile chlorides. Sodium's colour is so intense and so ubiquitous that traces mask other elements.

1860 年本生和基尔霍夫在研究焰色时用分光镜分析火焰光谱，发现每种元素都有特征谱线，并由此发现了铯（蓝色谱线，拉丁语“天蓝”）和铷（红色谱线，拉丁语“深红”），开创了光谱分析。焰色反应原理应用于烟花（锶盐红色、钡盐绿色、铜盐蓝色、钠盐黄色）、钠灯照明，并发展为原子发射光谱和火焰光度法。

In 1860 Bunsen and Kirchhoff, studying flame colours with a spectroscope, found that every element has characteristic lines, and discovered caesium (from its blue lines, Latin caesius, sky blue) and rubidium (from its red lines, Latin rubidus, deep red), founding spectral analysis. The principle colours fireworks (strontium red, barium green, copper blue, sodium yellow), lights sodium lamps, and developed into atomic emission spectroscopy and flame photometry.