Barium chloride is an inorganic compound with the formula . It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is a white powder, highly toxic, and imparts a yellow-green coloration to a flame. It is also hygroscopic, converting to the dihydrate , which are colourless crystals with a bitter salty taste. It has limited use in the laboratory and industry. Preparation On an industrial scale, barium chloride is prepared via a two step process from barite (barium sulfate). The first step requires high temperatures. The second step requires reaction between barium sulfide and hydrogen chloride: or between barium sulfide and calcium chloride: In place of HCl, chlorine can be used. Barium chloride is extracted out from the mixture with water. From water solutions of barium chloride, its dihydrate () can be crystallized as colorless crystals. Barium chloride can in principle be prepared by the reaction between barium hydroxide or barium carbonate with hydrogen chloride. These basic salts react with hydrochloric acid to give hydrated barium chloride. Structure and properties crystallizes in two forms (polymorphs). One form has the cubic fluorite () structure and the other the orthorhombic cotunnite () structure. Both polymorphs accommodate the preference of the large ion for coordination numbers greater than six. The coordination of is 8 in the fluorite structure and 9 in the cotunnite structure. When cotunnite-structure is subjected to pressures of 7–10 GPa, it transforms to a third structure, a monoclinic post-cotunnite phase. The coordination number of increases from 9 to 10. In aqueous solution behaves as a simple salt; in water it is a 1:2 electrolyte and the solution exhibits a neutral pH. Its solutions react with sulfate ion to produce a thick white precipitate of barium sulfate. Oxalate effects a similar reaction: When it is mixed with sodium hydroxide, it gives barium hydroxide, which is moderately soluble in water. is stable in the air at room temperature, but loses one water of crystallization above , becoming , and becomes anhydrous above . may be formed by shaking the dihydrate with methanol. readily forms eutectics with alkali metal chlorides. Uses Although inexpensive, barium chloride finds limited applications in the laboratory and industry. In industry, barium chloride is mainly used in the purification of brine solution in caustic chlorine plants and also in the manufacture of heat treatment salts, case hardening of steel. It is