Potassium sulfate (in British English potassium sulphate (SOP), also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is the inorganic compound with formula K2SO4. It is a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and a source of sulfur.Structure of β-K2SO4.Coordination sphere of one of two types of K+ site.SO4 environment in β-K2SO4. Potassium sulfate (in British English potassium sulphate (SOP), also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is the inorganic compound with formula K2SO4. It is a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and a source of sulfur. Potassium sulfate (K2SO4) has been known since early in the 14th century. It was studied by Glauber, Boyle, and Tachenius. In the 17th century, it was named arcanuni or sal duplicatum, as it was a combination of an acid salt with an alkaline salt. It was also known as vitriolic tartar and Glaser's salt or sal polychrestum Glaseri after the pharmaceutical chemist Christopher Glaser who prepared it and used medicinally. Known as arcanum duplicatum ('double secret') or panacea duplicata in pre-modern medicine, it was prepared from the residue (caput mortuum) left over from the production of aqua fortis, by dissolving the residue in hot water, filtering, and evaporating it to a cuticle. It was then left to crystallise. It was used as a diuretic and sudorific. According to Chambers's Cyclopedia, the recipe was purchased for five hundred thalers by Charles Frederick, Duke of Holstein-Gottorp. Schroder, the duke's physician, wrote wonders of its great uses in hypochondriacal cases, continued and intermitting fevers, stone, scurvy, etc. The mineral form of potassium sulfate, arcanite, is relatively rare. Natural resources of potassium sulfate are minerals abundant in the Stassfurt salt. These are cocrystallizations of potassium sulfate and sulfates of magnesium calcium and sodium.