Magnesium sulfate
IUPAC name	Magnesium sulfate (anhydrous); Magnesium sulfate heptahydrate
Other names	Magnesium sulphate; Epsom salts; bitter salts
Identifiers
CAS number	7487-88-9
ChemSpider ID	22515
Properties
Molecular formula	MgSO4 (anhydrous); MgSO4·7H2O
Molar mass	120.415 g/mol; 246.47g/mol (with water)
Appearance	white crystalline solid
Density	2.66 g/mL, solid
Melting point	1124°C decomp.
Solubility in water	25.5 g/100 ml (20 °C)
Structure
Crystal structure	monoclinic (hydrate)
Hazards
MSDS	External MSDS
Related compounds
Other cations	Calcium sulfate; aluminium sulfate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Magnesium sulfate is a chemical compound containing magnesium and sulfate, with the formula MgSO₄. In its hydrated form the pH is 6.0 (5.5 to 7.0). It is often encountered as the heptahydrate, MgSO₄·7H₂O, commonly called Epsom salts. Anhydrous magnesium sulfate is used as a drying agent. Since the anhydrous form is hygroscopic (readily absorbs water from the air) and therefore harder to weigh accurately, the hydrate is often preferred when preparing solutions, for example in medical preparations. Epsom salts have been traditionaly used as a component of bath salts.

Properties

Magnesium sulfate makes an important contribution to the absorption of sound in seawater.¹

Occurrence

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. Almost all known mineralogical forms of MgSO₄ occur as hydrates. Epsomite is the natural analogue of "Epsom salt," mentioned above. Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO₄·7H₂O, 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.

Applications

In agriculture and gardening, magnesium sulfate is used to correct magnesium deficiency in soil (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, and peppers. 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 as in bath salts, particularly in flotation therapy where high concentrations raise the bath water's specific gravity, effectively making the body more buoyant. This property is also used to restore some Lava lamps damaged by being shaken by exchanging the water and adding drops of a concentrated solution until sustainable buoyancy is reached. 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") 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 used in many bottled water ingredients. It may also be used as a coagulant for making tofu.²

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 magnesium stablizes these ions in the saltwater and prevents their spontaneous precipitation into calcium carbonate.³ It is also recommended for dropsy treatment for fish.⁴

An old remedy for diarrhea in adult chickens is 1/2 tsp per bird per day added to their feed.⁵

Medical use

Further information: Hypomagnesemia

Oral magnesium sulfate, or magnesium hydroxide, is commonly used as a saline laxative. Epsom salts are also available in a gel form for topical application in treating aches and pains.

Indications for its use are

• Replacement therapy for hypomagnesemia.
• Magnesium sulfate is the first-line antiarrhythmic agent for Torsades de pointes in cardiac arrest under the 2005 ECC guidelines as well as managing Quinidine-induced arrythmias.
• As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma.⁶ Recent studies have revealed that magnesium sulfate can be nebulized to reduce the symptoms of acute asthma.⁶ It is commonly administered via the intravenous route for the management of severe asthma attacks.
• Users of Epsom salts in the gel form have reported significant and lasting reduction of pain associated with fibromyalgia and osteoporosis.⁷
• A 2004 research study showed that both magnesium and sulfate are absorbed through the skin when bathing in 1% solution.⁸
• Magnesium sulfate can be used to treat pre-eclampsia in pregnant women.⁹
• Magnesium sulfate can also delay labor in the case of premature labor, to delay preterm birth.
• Intravenous magnesium sulfate may be able to prevent cerebral palsy in preterm babies.¹⁰
• Solutions of sulfate salts such as Epsom salts may be given as first aid for barium poisoning.
• Magnesium sulfate paste has been used as an agent for dehydrating (drawing) boils, carbuncles and abscesses.
• Magnesium sulfate solution has also been shown to be an effective aid in the fight against blemishes and acne when applied directly to problematic areas, usually in poultice form.
• Magnesium sulfate when used through soaking, can soothe muscle pains and help improve rough patches in the skin.
• The body's magnesium level increases when soaking with magnesium sulfate which is necessary for serotonin, a mood-regulating neurotransmitter that may increase feelings of relaxation and well-being.¹¹
• Soaking in a warm bath containing Epsom Salt (magnesium sulfate) can be beneficial to soothe and relieve Herpes outbreak symptoms, such as itching and lesions relating to Genital Herpes and Shingles.¹²¹³

References

1. ^ Underlying physics and mechanisms for the absorption of sound in seawater
2. ^ "Process for producing packed tofu".
3. ^ "Do-It-Yourself Magnesium Supplements for the Reef Aquarium". Reefkeeping (2006). Retrieved on 2008-03-14.
4. ^ "Dropsy". www.healthybetta.com (2004). Retrieved on 2007-05-20.
5. ^ "Old Time Remedies for Common Poultry Diseases". Mother Earth News (March 1974). Retrieved on 2008-03-05.
6. ^ ^{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.
7. ^ Epsom Salt in gel form [1] (republished by J. Drew & Associates, with permission), 2007
8. ^ Rosemary Waring Absorption of magnesium sulphate through the skin (republished by the Epsom Salt Council), 2004
9. ^ BBC News story 'Simple jab averts pregnancy danger' [2] 30 May 2002
10. ^ Epsom salt can prevent cerebral palsy: U.S. study
11. ^ "Epsom Salt Industry Council - About Epsom Salt - The Science of Epsom Salt" Epsom Salt Council
12. ^ "Herpes Home Remedies" Herpes and Cold Sores Support Network
13. ^ "McKinley Health Center - Genital Herpes - University of Illinois" McKinley Health Center, University of Illinois