cupric sulfate (kōō´prĬk sŭl´fāt, kyōō´–) or copper (II) sulfate, chemical compound, CuSO4, taking the form of white rhombohedral crystals or amorphous powder. It decomposes at 650°C to cupric oxide (CuO). It is fairly soluble in water and when dissolved forms the pentahydrate, CuSO4·5H2O, the form that is most familiar. The pentahydrate can be collected as blue triclinic crystals; it is also known as blue vitriol. It loses part of its water of crystallization when heated to 110°C and fully dehydrates at 150°C. Cupric sulfate is used in copperplating, in dyeing (as a mordant), in wet-cell batteries, in pigments, and in insecticides, fungicides, and algicides. It is insoluble in alkali solutions, a property used in the preparation of Bordeaux mixture; lime (calcium hydroxide) is added to moist cupric sulfate, forming a basic cupric sulfate precipitate (a mixture of cupric sulfate and cupric hydroxide). The anhydrous sulfate is used to detect the presence of water in certain organic liquids; it turns into the blue pentahydrate, e.g., when added to alcohol that contains water. Cupric sulfate is prepared by the action of warm dilute sulfuric acid (oil of vitriol) on copper metal or cupric oxide; it is also a byproduct of copper sulfide ore refining. It occurs naturally in the minerals chalcanthite (the pentahydrate), hydrocyanite (the anhydrous sulfate), and brochantite (a basic sulfate, CuSO4·3Cu(OH)2).