Bromine (symbol Br, atomic weight 79.96), a chemical element of the halogen group, which takes its name from its pungent unpleasant smell (βρῶμος, a stench). It was first isolated by A.J. Balard in 1826 from the salts in the waters of the Mediterranean. He established its elementary character, and his researches were amplified by K.J. Löwig (1803-1890) in Das Brom und seine chemischen Verhaltnisse (1829). Bromine does not occur in nature in the uncombined condition, but in combination with various metals is very widely but sparingly distributed. Potassium, sodium and magnesium bromides are found in mineral waters, in river and sea-water, and occasionally in marine plants and animals. Its chief commercial sources are the salt deposits at Stassfurt in Prussian Saxony, in which magnesium bromide is found associated with various chlorides, and the brines of Michigan, Ohio, Pennsylvania and West Virginia, U.S.A.; small quantities are obtained from the mother liquors of Chile saltpetre and kelp.
In combination with silver it is found as the mineral bromargyrite (bromite).
The chief centres of the bromine industry are Stassfurt and the central district of Michigan. It is manufactured from the magnesium bromide contained in "bittern" (the mother liquor of the salt industry), by two processes, the continuous and the periodic. The continuous process depends upon the decomposition of the bromide by chlorine, which is generated in special stills. A regular current of chlorine mixed with steam is led in at the bottom of a tall tower filled with broken bricks, and there meets a descending stream of hot bittern: bromine is liberated and is swept out of the tower together with some chlorine, by the current of steam, and then condensed in a worm. Any uncondensed bromine vapour is absorbed by moist iron borings, and the resulting iron bromide is used for the manufacture of potassium bromide. The periodic process depends on the interaction between manganese dioxide (pyrolusite), sulphuric acid, and a bromide, and the operation is carried out in sandstone stills heated to 60° C., the product being condensed as in the continuous process. The substitution of potassium chlorate for pyrolusite is recommended when calcium chloride is present in the bittern.
The crude bromine is purified by repeated shaking with potassium, sodium or ferrous bromide and subsequent redistillation. Commercial bromine is rarely pure, the chief impurities present in it being chlorine, hydrobromic acid, and bromoform (M. Hermann, Annalen, 1855, 95, p. 211). E. Gessner (Berichte, 1876, 9, p. 1507) removes chlorine by repeated shaking with water, followed by distillation over sulphuric acid; hydrobromic acid is removed by distillation with pure manganese dioxide, or mercuric oxide, and the product dried over sulphuric acid. J.S. Stas, in his stoichiometric researches, prepared chemically pure bromine from potassium bromide, by converting it into the bromate which was purified by repeated crystallization. By heating the bromate it was partially converted into the bromide, and the resulting mixture was distilled with sulphuric acid. The distillate was further purified by digestion with milk of lime, precipitation with water, and further digestion with calcium bromide and barium oxide, and was finally redistilled.