Sodium Sulfide is the chemical compound with the formula Na₂S, or more commonly its hydrate Na₂S·9H₂O. Both are   colorless water-soluble salts that give strongly alkaline solutions. When exposed to moist air, Na₂S and its hydrates   emit hydrogen sulfide, which smells like rotten eggs. Some commercial samples are specified as Na₂S·xH₂O, where a weight percentage of Na₂S is specified. Commonly available grades have around 60% Na₂S by weight, which means that x is around 3. Such technical grades of sodium sulfide have a yellow appearance owing to the presence of polysulfides. These grades of sodium sulfide are marketed as 'sodium sulfide flakes'. Although the solid is yellow, solutions of it are colorless.

Applications

Sodium sulfide is primarily used in pulp and paper industry in the Kraft process.

It is used in water treatment as an oxygen scavenger agent and also as a metals precipitant, in chemical photography for toning black and white photographs, in textile industry as a bleaching, and as a desulfurising and as a dechlorinating agent and in leather trade for the sulfitisation of tanning extracts. It is used in chemical manufacturing as a sulfonation and sulfomethylation agent. It is used in the production of rubber chemicals, sulfur dyes and other chemical compounds. It is used in other applications including ore flotation, oil recovery, making dyes, and detergent.It is also used for leather processing in liming operation as unhairing agent.