Sodium sulfideis achemical compoundwith theformulaNa2S, or more commonly itshydrateNa2S9H2O. Both the anhydrous and the hydrated salts in pure crystalline form are colorless solids, although technical grades of sodium sulfide are generally yellow to brick red owing to the presence ofpolysulfidesand commonly supplied as a crystalline mass, in flake form, or as a fused solid. They are water-soluble, giving stronglyalkalinesolutions. When exposed to moisture, Na2S immediately hydrates to givesodium hydrosulfide.