Sodium polysulfide

Sodium polysulfide is a general term for salts with the formula Na₂S_x, where x = 2 to 5. The species S_x, called polysulfide anions, include disulfide (S₂), trisulfide (S₃), tetrasulfide (S₄), and pentasulfide (S₅). In principle, but not in practice, the chain lengths could be longer. The salts are dark red solids that dissolve in water to give highly alkaline and corrosive solutions. In air, these salts oxidize, and they evolve hydrogen sulfide by hydrolysis.