Magnesium sulfate

Magnesium sulfate
Magnesium sulfate

Anhydrous magnesium sulfate

Epsomite (heptahydrate)
CAS number 7487-88-9 YesY, 14168-73-1 (monohydrate), 24378-31-2 (tetrahydrate), 15553-21-6 (pentahydrate), 13778-97-7 (hexahydrate), 10034-99-8 (heptahydrate)
PubChem 24083
ChemSpider 22515 YesY
DrugBank DB00653
ChEBI CHEBI:32599 YesY
RTECS number OM4500000
Jmol-3D images Image 1
Molecular formula MgSO4
Molar mass 120.366 g/mol (anhydrous)
246.47 g/mol (heptahydrate)
Appearance white crystalline solid
Density 2.66 g/cm3 (anhydrous)
2.445 g/cm3 (monohydrate)
1.68 g/cm3 (heptahydrate)
1.512 g/cm3 (11-hydrate)
Melting point

1124 °C (anhydrous, decomp)
200 °C (monohydrate, decomp)
150 °C (heptahydrate, decomp)
2 °C (11-hydrate, decomp)

Solubility in water anhydrous
269 g/L (0 °C)
255 g/L (20 °C)
710 g/L (20 °C)
Solubility 0.116 g/L (18 °C, ether)
slightly soluble in alcohol, glycerol
insoluble in acetone
Refractive index (nD) 1.523 (monohydrate)
1.433 (heptahydrate)
Crystal structure monoclinic (hydrate)
MSDS External MSDS
EU Index Not listed
Related compounds
Other cations Beryllium sulfate
Calcium sulfate
Strontium sulfate
Barium sulfate
 N sulfate (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Magnesium sulfate (or magnesium sulphate) is a chemical compound containing magnesium, sulfur and oxygen, with the formula MgSO4. It is often encountered as the heptahydrate epsomite (MgSO4·7H2O), commonly called Epsom salt, from the town of Epsom in Surrey, England, where the salt was distilled from the springs that arise where the porous chalk of the North Downs meets non-porous London clay. Another hydrate form is kieserite.

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 preferred when preparing solutions, for example in medical preparations. Epsom salt has been traditionally used as a component of bath salts.



Magnesium sulfate is the primary substance that causes the absorption of sound in seawater.[1] Absorption, in this case, means the conversion of acoustic energy to heat energy. The conversion is a strong function of frequency. Lower frequencies are less affected by the salt, so that the acoustic energy travels much farther in the ocean. Boric acid also contributes to absorption; but the most abundant salt in seawater, sodium chloride, has no known effect on 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,[2] was also 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 never treated as a mineral.

The pH of hydrates is average 6.0 (5.5 to 6.5). Magnesium hydrates have, like Copper(II) sulfate, coordinated water.[3]


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.


In agriculture and gardening, magnesium sulfate is used to correct magnesium deficiency in soil, since magnesium is an essential element in the chlorophyll molecule. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, tomatoes, peppers and cannabis. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility.

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 ("pruning" – partial maceration) which is caused by prolonged immersion of extremities in pure water. However, magnesium sulfate can also be absorbed into the skin, reducing inflammation. It is also sometimes found in bottled mineral water, and accordingly is sometimes listed in the contents thereof.[citation needed]

It may also be used as a coagulant for making tofu.[4]

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.[5]

Magnesium sulfate is used as a reactive compound in the manufacture of black powder where it contributes to a violent burn rate thus reducing material costs.[citation needed]

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:

Cu + MgSO4 + 2 H2O → H2 + CuSO4 + Mg(OH)2.[citation needed]

Magnesium sulfate is used as a brewing salt in beer production to adjust the ion content of the brewing water and enhance enzyme action in the mash or promote a desired flavor profile in the beer.

Medical use

Oral magnesium sulfate is commonly used as a saline laxative or osmotic purgatives. Epsom salt is also available in a gel form for topical application in treating aches and pains.

Indications for its internal use are:

  • Replacement therapy for hypomagnesemia.[6]
  • Magnesium sulfate is the first-line antiarrhythmic agent for torsades de pointes in cardiac arrest under the 2005 ECC guidelines and for managing quinidine-induced arrhythmias.[7]
  • As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma.[8] Recent studies have revealed that magnesium sulfate can be nebulized to reduce the symptoms of acute asthma.[8] It is commonly administered via the intravenous route for the management of severe asthma attacks.
  • Magnesium sulfate can be used to treat eclampsia in pregnant women.[9]
  • Magnesium sulfate can also delay labor in the case of premature labor, to delay preterm birth.[10][11]
  • Intravenous magnesium sulfate may be able to prevent cerebral palsy in preterm babies.[12]
  • Solutions of sulfate salts such as Epsom salt may be given as first aid for barium chloride poisoning.[13]

Indications for topical use are

  • Soaking in a warm bath containing Epsom salt (magnesium sulfate) can be beneficial to soothe, relax, and relieve herpes outbreak symptoms, such as itching and lesions relating to genital herpes and shingles.[14][15]
  • A 2004 research study showed that both magnesium and sulfate are absorbed through the skin when bathing in 1% w/v solution.[16]

See also


  1. ^ "Underlying physics and mechanisms for the absorption of sound in seawater". Retrieved 2009-07-06. 
  2. ^ Peterson, Ronald C.; Hammarstrom, Jane M.; Seal, II, Robert R (Feb 2006). "Alpersite (Mg,Cu)SO4·7H2O, a new mineral of the melanterite group, and cuprian pentahydrite: Their occurrence within mine waste". American Mineralogist 91 (2-3): 261–269. doi:10.2138/am.2006.1911. 
  3. ^ Lucia Odochian Study of the nature of the crystallization water in some magnesium hydrates by thermal methods J. of Thermal Analysis and Calorimetry ; Volume 45, Number 6 / December, 1995. doi:10.1007/BF02547437
  4. ^ "Process for producing packed tofu". 
  5. ^ "Do-It-Yourself Magnesium Supplements for the Reef Aquarium". Reefkeeping. 2006. Retrieved 2008-03-14. 
  6. ^ "Pharmaceutical Information - MAGNESIUM SULFATE". RxMed. Retrieved 2009-07-06. 
  7. ^ "When clicking citation, it is listed under ''Other medicinal and home uses''". 2007-01-04. Retrieved 2009-07-06. 
  8. ^ a b Blitz M, Blitz S, Hughes R, Diner B, Beasley R, Knopp J, Rowe BH. Aerosolized magnesium sulfate for acute asthma: a systematic review. Chest 2005;128:337-44. PMID 16002955.
  9. ^ jab averts pregnancy danger', BBC News, 30 May 2002
  10. ^ "Magnesium sulfate for preterm labor". 2007-01-19. Retrieved 2009-07-06. 
  11. ^ Lewis DF (September 2005). "Magnesium sulfate: the first-line tocolytic". Obstet. Gynecol. Clin. North Am. 32 (3): 485–500. doi:10.1016/j.ogc.2005.03.002. PMID 16125045. 
  12. ^ "Epsom salt can prevent cerebral palsy: U.S. study". 2008-01-31. Retrieved 2009-07-06. 
  13. ^ "BARIUM CHLORIDE DIHYDRATE 4. First Aid Measures". Retrieved 2009-07-06. 
  14. ^ "Herpes Home Remedies" Herpes and Cold Sores Support Network
  15. ^ "McKinley Health Center - Genital Herpes - University of Illinois" McKinley Health Center, University of Illinois
  16. ^ Rosemary Waring Absorption of magnesium sulphate through the skin (republished by the Epsom Salt Council), 2004

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Look at other dictionaries:

  • magnesium sulfate — n a white anhydrous salt MgSO4 that occurs naturally in hydrated form as Epsom salts and that in the hydrated form MgSO4·7H2O is administered orally to relieve constipation or by injection to treat magnesium deficiency, to control convulsions… …   Medical dictionary

  • magnesium sulfate — noun a salt of magnesium • Hypernyms: ↑sulfate, ↑sulphate • Hyponyms: ↑Epsom salts, ↑bitter salts * * * noun : any of several sulfates of magnesium; especially …   Useful english dictionary

  • magnesium sulfate — magnio sulfatas statusas T sritis chemija formulė MgSO₄ atitikmenys: angl. magnesium sulfate rus. магний сернокислый; магния сульфат ryšiai: sinonimas – magnio tetraoksosulfatas …   Chemijos terminų aiškinamasis žodynas

  • magnesium sulfate — A drug used to treat pre eclampsia and eclampsia (serious complications of pregnancy). Magnesium sulfate is also being studied for its ability to prevent the toxic side effects of certain drugs used to treat colorectal cancer. It is a type of… …   English dictionary of cancer terms

  • magnesium sulfate heptahydrate — magnio sulfatas heptahidratas statusas T sritis chemija formulė MgSO₄·7H₂O atitikmenys: angl. bitter salt; Epsom salt; magnesium sulfate heptahydrate rus. английская соль; горькая соль; магния сульфата гептагидрат ryšiai: sinonimas – magnio… …   Chemijos terminų aiškinamasis žodynas

  • magnesium sulfate — noun Date: 1869 a sulfate of magnesium: as a. a white salt MgSO4 used in medicine and in industry b. Epsom salts …   New Collegiate Dictionary

  • magnesium sulfate — noun The magnesium salt of sulfuric acid (chemical formula MgSO), commonly called Epsom salts. Syn: E518, food additive …   Wiktionary

  • magnesium sulfate — Chem. a white, water soluble salt, MgSO4, used chiefly in medicine and in the processing of leather and textiles. Cf. Epsom salt. [1885 90] * * * …   Universalium

  • magnesium sulfate — magne′sium sul′fate n. chem. a water soluble salt, MgSO4, used in medicine and in processing leather and textiles Compare Epsom salt …   From formal English to slang

  • Sulfate de magnesium — Sulfate de magnésium Sulfate de magnésium Sulfate de magnésium anhydre Général Nom IUPAC Sulfate …   Wikipédia en Français

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