Magnesium sulfate (or magnesium sulphate, Epsom salt, Bitter salt ) is a chemical compound containing magnesium, sulfur and oxygen, with the formula Mgso4. In its hydrated form, the pH is 6.0(5.5-6.5). It is often encountered as the heptahydrate, Mgso47H2O, commonly called Epsom salt. Anhydrous magnesium sulfate is used as a drying agent. Since the anhydrous form is hygroscopic (readily absorbs water from the air )and is therefore difficult to weigh accurately, the hydrate is often prefered when reparing solutions, for example, in medical preparations, Epsom salt has been traditionally used as a component of bath salts.