Magnesium is the silvery-white metal associated with the blinding light of photographic flash bulbs, the construction of lightweight-alloy airplanes and the food producing chemical, chlorophyll, found in green plants. Especially since the 1990s, research has been conducted concerning the connection between magnesium and the immune system. Sulfuric acid is a completely different sort of substance: an important, powerfully dehydrating, oxygenated or “oxy-” acid. The reaction between magnesium and sulfuric acid, yields magnesium sulfate and water, Mg + H2SO4 → MgSO4 + H2O. Crystallized heptahydrate of magnesium sulfate, MgSO4·7H2O, better known as Epsom salt is used in farming, gardening, and medicine.
Instead of the metal, magnesium and sulfuric acid can be united using the oxide (MgO, the hydroxide (Mg(OH)2) or the carbonate (MgCO3), without having to be purified to get rid of side products. The reaction using the carbonate, for instance, is written MgCO3 + H2SO4 → MgSO4 + CO2↑ + H2O. Carbon dioxide gas escapes to the atmosphere. If desired for some specialty use, a double displacement reaction can be used, for example MgCl2 + Na2SO4 → MgSO4 + 2 NaCl.
Although Epsom salt is readily produced in the laboratory using a form of magnesium and sulfuric acid, writings indicate it was first in the 17th Century its presence was noted, in well-water – although its chemical identity was not recognized at that time. The well from which the water was taken was located in Epsom, a town in Surrey, England. Travelers still visit the well, since its structure has been restored. Among famous early visitors to the Epsom well was Plague-historian Samuel Pepys. It should be mentioned that the mineral waters containing the reaction product of magnesium and sulfuric acid are not and were not limited to just the town of Epsom, but are located in other wells around London as well, including ones in Acton, Dulwich and Streatham.
Salt deposits are doubtless produced through the weathering of rock and clay soil, the resulting magnesium sulfate’s water solubility causing it to rise to the surface where any moisture evaporates. The resulting mineral deposit, Epsom salt is called Epsomite, although there are other forms as well, varying in the water of hydration, such as hexahydrite (MgSO4·6H2O). Some of these deposits exist as white efflorescence, occurring in caves and around volcanoes. It can also be found as lake-bed deposits.
Epsom salt is used agriculturally to reduce magnesium deficiency in the soil, while providing a degree of acidity. Medically, it can be used as a cathartic or purge, though caution must be used. It is also used externally as a soak, some claiming it provides a measure of soothing and comfort, and in some instances, health benefits to those who may be “deficient in sulfate,” perhaps some with autism. Still others attribute to this product of magnesium and sulfuric acid, the ability to improve acne.