Barium bromide
Barium bromide is the chemical compound with the formula BaBr. Like barium chloride, it dissolves well in water and is toxic. Structure and properties. BaBr crystallizes in the lead chloride (cotunnite) motif, giving white orthorhombic crystals that are deliquescent. In aqueous solution BaBr behaves as a simple salt. Solutions of barium bromide reacts with the sulfate salts to produce a solid precipitate of barium sulfate. Similar reactions occur with oxalic acid, hydrofluoric acid, and phosphoric acid, giving solid precipitates of barium oxalate, fluoride, and phosphate, respectively. Preparation. Barium bromide can be prepared by treating barium sulfide or barium  carbonate with hydrobromic acid: Barium bromide crystallizes from concentrated aqueous solution in its dihydrate , BaBr·2HO. Heating this dihydrate to 120 °C gives the anhydrous salt. Uses. Barium bromide is a precursor to chemicals used in photography and to other bromides. Historically, barium bromide was used to purify radium in a process of fractional crystallization devised by Marie Curie. Since radium precipitates preferentially in a solution of barium bromide, the ratio of radium to barium in the precipitate would be higher than the ratio in the solution. Safety. Barium bromide, along with other water-soluble barium salts, is toxic. Barium