Magnesium sulfate (or magnesium sulphate) is an inorganicsalt (chemical compound) containing magnesium, sulfur and oxygen, with the formula MgSO4. It is often encountered as the heptahydrate sulfate mineralepsomite (MgSO4·7H2O), commonly called Epsom salt, taking its name from a bitter saline spring in Epsom in Surrey, England, where the salt was produced from the springs that arise where the porous chalk of the North Downs meets non-porous London clay. The monohydrate, MgSO4·H2O is found as the mineral kieserite. The overall global annual usage in the mid-1970s of the monohydrate was 2.3 million tons, of which the majority was used in agriculture.
Anhydrous magnesium sulfate is used as a drying agent. The anhydrous form is hygroscopic (readily absorbs water from the air) and is therefore difficult to weigh accurately; the hydrate is often preferred when preparing solutions (for example, in medical preparations). Epsom salt has been traditionally used as a component of bath salts. Epsom salt can also be used as a beauty product. Athletes use it to soothe sore muscles, while gardeners use it to improve crops. It has a variety of other uses. Epsom salt is also effective in the removal of splinters.
As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma, magnesium sulfate can be nebulized to reduce the symptoms of acute asthma. It is commonly administered via the intravenous route for the management of severe asthma attacks.
Magnesium sulfate is effective in decreasing the risk that pre-eclampsia progresses to eclampsia. IV magnesium sulfate & diazepam is used to prevent and treat seizures of eclampsia. It is also commonly used for eclampsia where compared to diazepam or phenytoin it results in better outcomes.
In those who are at risk of a preterm birth. A systematic review suggested that intravenous magnesium sulfate before birth could reduce the risk of cerebral palsy and motor dysfunction in preterm infants by 30%.
Magnesium sulfate has been used as an experimental treatment of Irukandji syndrome caused by envenomation by certain species of Irukandji jellyfish, but the efficacy of this treatment remains unproven.
Solutions of sulfate salts such as Epsom salt may be given as first aid for barium chloride poisoning.
Magnesium sulfate was once used as a tocolytic, but meta-analyses have failed to support it as an anti-contraction medication. And its use for prolonged periods (more than five to seven days) may result in health problems for the baby.
In those at risk of an early delivery, magnesium sulfate appears to decrease the risk of cerebral palsy. It is unclear if it helps those who are born at term.
Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis due to its affinity for water. During work-up, an organic phase is saturated with magnesium sulfate until it no longer forms clumps. The hydrated solid is then removed with filtration or decantation. Other inorganic sulfate salts such as sodium sulfate and calcium sulfate may also be used in the same way.
Magnesium sulfate is used in bath salts, particularly in flotation therapy, where high concentrations raise the bath water's specific gravity, effectively making the body more buoyant. Traditionally, it is also used to prepare foot baths, intended to soothe sore feet. The reason for the inclusion of the salt is partially cosmetic: the increase in ionic strength prevents some of the temporary skin wrinkling (partial maceration) which is caused by prolonged immersion of extremities in pure water. It is also a common belief that magnesium sulfate can be absorbed into the skin, reducing inflammation. However, no scientific study has ever been published to either explain or reaffirm this belief. It is naturally present in some mineral waters.
It may also be used as a coagulant for making tofu.
Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals, as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium, calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate.
Magnesium sulfate is used as the electrolyte to prepare copper sulfate. A magnesium sulfate solution is electrolyzed with a copper anode to form copper sulfate, magnesium hydroxide, and hydrogen:
Magnesium sulfate is highly soluble in water. The anhydrous form is strongly hygroscopic, and can be used as a desiccant. It is the primary substance that causes the absorption of sound in seawater (acoustic energy is converted to thermal energy). Absorption is strongly dependent on frequency: lower frequencies are less absorbed by the salt, so that the sound travels much farther in the ocean. Boric acid also contributes to absorption, but the most abundant salt in seawater, sodium chloride, has negligible sound absorption.
Almost all known mineralogical forms of MgSO4 occur as hydrates. Epsomite is the natural analogue of "Epsom salt". Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO4·7H2O, was recently recognized. Both are, however, not the highest known hydrates of MgSO4, due to the recent terrestrial find of meridianiite, MgSO4·11H2O, which is thought to also occur on Mars. Hexahydrite is the next lower (6) hydrate. Three next lower hydrates — pentahydrite (5), starkeyite (4) and especially sanderite (2) — are more rarely found. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps, but was never treated as a mineral.
Magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium-magnesium (K-Mg) salts deposits.
^Duley, L; Gülmezoglu, AM; Henderson-Smart, DJ; Chou, D (Nov 10, 2010). "Magnesium sulphate and other anticonvulsants for women with pre-eclampsia.". The Cochrane database of systematic reviews (11): CD000025. doi:10.1002/14651858.CD000025.pub2. PMID21069663.
^Doyle, LW; Crowther, CA; Middleton, P; Marret, S; Rouse, D (Jan 21, 2009). "Magnesium sulphate for women at risk of preterm birth for neuroprotection of the fetus.". The Cochrane database of systematic reviews (1): CD004661. doi:10.1002/14651858.CD004661.pub3. PMID19160238.
^Wolf, HT; Hegaard, HK; Greisen, G; Huusom, L; Hedegaard, M (Feb 2012). "Treatment with magnesium sulphate in pre-term birth: a systematic review and meta-analysis of observational studies.". Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology32 (2): 135–40. doi:10.3109/01443615.2011.638999. PMID22296422.
^Nguyen, TM; Crowther, CA; Wilkinson, D; Bain, E (Feb 28, 2013). "Magnesium sulphate for women at term for neuroprotection of the fetus.". The Cochrane database of systematic reviews2: CD009395. doi:10.1002/14651858.cd009395.pub2. PMID23450601.
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