Manganese sulphate, polarised light micrograph. Magnesium sulphate, an inorganic salt (MgSO4). Epsom salts are a hydrated form of magnesium sulphate with seven water molecules (heptahydrate). With its high capacity to extract water, magnesium sulphate is used as one of the best drying agents. Epsom salts form a component of bath salts. Magnesium is an important trace element which plays a role as an electrolyte, regulating the control of enzymes in the body. Magnesium sulphate is also used as plant food to accelerate the growth of vegetables. Magnification: x70 when printed 10 centimetres wide.