Potassium sulphate «Poluks Group» (K₂SO₄) (in British English potassium sulphate, also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is a non-flammable white crystalline salt which is soluble in water. The chemical compound is commonly used in fertilizers, providing both potassium and sulfur.

It is mainly used for chlorine sensitive crops (potatoes, tobacco, flax, grapes, citrus fruits, etc.). The presence of sulfate ions in the fertilizer has a positive effect on the productivity of cruciferous plants (cabbage, rutabagas, turnips, etc.) and legumes that consume a lot of sulfur. Potassium sulfate is also used in the production of glass, various alum and other potassium compounds as a flux in metallurgy.