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potassium sulfide[pə′tas·ē·əm ′səl‚fīd]
K2S, a salt; colorless crystals. Density, 1.80 g/cm3; melting point, 471°C.
Potassium sulfide is hygroscopic and highly water-soluble. It readily oxidizes on exposure to atmospheric oxygen to potassium thiosulfate, K2S2O3. Boiling aqueous potassium sulfide with excess sulfur forms the potassium polysulfides K2S2, K2S3, K2S4, K2S5, and K2S6. Potassium sulfide is obtained by the reactions:
KOH + H2S = KHS + H2O
and KHS + KOH = K2S + H2O
The fusion of potash with sulfur results in the formation of sulfurated potash, a mixture of potassium polysulfides and thiosulfates, which is used in the preparation of sulfur baths. Potassium sulfide is also used in photography.