Sodium sulfide is the
chemical compound with the
formula Na2S, or more commonly its
hydrate Na
2S·9
H2O. Both are colorless water-soluble salts that give strongly
alkaline solutions. When exposed to moist air, Na
2S and its hydrates emit
hydrogen sulfide, which smells like rotten eggs. Some commercial samples are specified as Na
2S·
xH
2O, where a weight percentage of Na
2S is specified. Commonly available grades have around 60% Na
2S 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.