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Magnesium sulfate

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Magnesium sulfate

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Magnesium sulfate
Anhydrous magnesium sulfate
Systematic name Magnesium sulfate
Other names Epsom salts
bitter salts
Molecular formula MgSO47H2O
Formula weight 120.36 g/mol (anhydrous)
246.48 g/mol (Heptahydrate)
Appearance white crystalline solid
CAS number 7487-88-9(anhydrous)
Density and phase g/cm3, solid
Solubility in water 25.5 g/100 ml (20 C)
In ethanol Slightly soluble (anh.)
Insoluble (hydrate)
Melting point 1124C decomp.
Dehydration Temperature 250C
Crystal structure monoclinic (hydrate)
Related compounds
Other cations Calcium sulfate
Aluminium sulfate
Except where noted otherwise, data are given for
materials in their standard state (at 25C, 100 kPa)

Magnesium sulfate or Magnesium sulfate heptahydrate or Epsom salt is a chemical compound containing magnesium, with the formula MgSO47H2O. Magnesium sulfate without water of crystalization MgSO4 is available as a far less common chemical and drying agent, but typically "magnesium sulfate" refers to the hydrate, and Epsom salt always refers to the hydrate. In medical preparations the hydrate form is used to prepare and label even magnesium sulfate formulas in water solution, because the hydrate crystals, which are not deliquescent, are far more easily weighed and subject to quality control in manufacture.



Epsom salt was originally prepared by boiling down mineral waters at Epsom, England, and afterwards prepared from sea water. In more recent times, these salts are obtained from certain minerals such as epsomite.

Agricultural use

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, and tomatoes. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility.

Medical use

Locally it may be used as a treatment of an ingrown nail. Oral magnesium sulfate, or magnesium oxide, is used as a laxative. Epsom salts are also available in a gel form for topical application in treating aches and pains. Intravenous use is broadening, as magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction, as well as other effects. Indications for its use are:

  • Hypomagnesemia (low magnesium concentrations in the blood)
  • In cardiac arrhythmias, most notably in:
    • Atrial fibrillation
      Torsades de pointes tachycardia
  • Treatment (and sometimes prevention) of seizures in eclampsia, for which it is the most effective therapy.
  • As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma.[1] In fact, recent studies have revealed that magnesium sulfate can be nebulized to reduce the symptoms of acute asthma (Blitz et al 2005). In the UK, it is commonly administered via the intravenous route for the management of severe asthma attacks
  • As a tocolytic agent, administered intravenously for the treatment of preterm labor.
  • For acute treatment of migraine.
  • In the treatment of tetanus
  • In the managment of phaeochromocytoma
Epsom salts
Epsom salts

Use in organic chemistry

Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis due to its affinity for water. During workup, an organic phase is saturated with magnesium sulfate until it no longer forms clumps. The hydrated solid is then removed with filtration or decantation.

A number of other inorganic sulfate salts, sodium sulfate and calcium sulfate for example, may also be used in the same way.

Other uses

Magnesium sulfate is used as in bath salts, particularly in floatation 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 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. Magnesium sulfate paste has been used as an agent for drawing (dehydrating) boils and carbuncles. In some parts of the world (such as New Zealand), it is added to homemade drinks, such as lemon cordials. Here the sulfate part of the salt is not important, rather it is the intensely sour taste of magnesium ion Mg2+ which acts as flavoring agent.

Also recomended for dropsy treatment for fishes.


  1. ^ 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.

External links

Epsom Salt Industry Council [[1]]

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