Reprinted from Chemistry in Action, Volume 40, Summer 1993.
Most of us are familiar with the phrase "taking it with a dose of salts," but not everyone knows what it means. It goes back to the practice of taking Epsom salts as a cure for constipation.
The medicinal value of the the spring waters at Epsom, Surrey was discovered in the rein of Elizabeth I (1558-1603) and the Epsom Spa grew in fame over the next half-century. Local tradition recounts the discovery of the spa in this way:
"One very dry summer a farmer dug around a spring to make a pool for his cattle to drink. However, the cattle would not drink although they were dying of thirst. He wondered why and tasted the water: it was bitter to the taste and kept the flies off."
The relaxing action of the water was soon discovered and by 1640 it was a famous spa. 'Epsome waters' were mentioned by Henry More in 1657 and Bergman said "the sal catharticus amarus has been in high esteem at Epsom from the year 1610" (quoted in Partington History of Chemistry, Volume 3). In 1695, Nehemiah Grew, a doctor in London wrote an account of the medicinal value and properties obtained from the spring entitled "A treatise on the Nature and Use of the Bitter Purging Salt contain'd in Epsom and such other waters." In 1700 George and Francis Moult established a factory at Shooter's Hill, near London, to market Epsom Salts. It was sold at the sign of the Glaubers-Head in Watling Street. By the middle of the 19th century the supply of mineral at Epsom was exhausted.
The active ingredient of the water was hydrated magnesium sulphate, which crystallized as MgSO4.7H2O, known as Epsom Salt(s) in England and sal anglicum (English salt) on the continent. In the early 19th century St. Bartholomew's Hospital in London used two and a half tons of Epsom Salts each year. When it occurs as a mineral the deposit is known as epsomite. There are large deposits at Stassfurt in Germany.
Epsom salts are still sold as an over-the-counter medicine. Magnesium sulphate is made industrially by neutralizing sulphuric acid with magnesium carbonate or hydroxide. It is used as a sizing agent in paper and as a fireproofing agent, as an ingredient in explosives and matches. Medicinally it is used as a mild laxative purgative) and as an antiinflammatory. Sea-water contains 1.668 g/L of magnesium sulphate.
I came across two rhymes illustrating the potency of Epsom Salts:
Mary had a pocket watch
She swallowed it one day
And now she's taking Epsom salts
To pass the time away.
The other is an epitaph, which also has a connection with Epsom salts:
Here lies the body of Mary Ann Lowder
Who burst while drinking a seidlitz powder;
Called from this Earth to her Heavenly rest
She should have waited until it effervesced.
(Epitaph from Burleigh, New Jersey ca. 1880)
What is a seidlitz powder? Seidlitz powder or salts were/are medicinal salts composed of tartaric acid, potassium tartrate and sodium carbonate. In the stomach or in water these will effervesce producing carbon dioxide. They were used to 'open' the bowels, in the same way Epsom Salts were used. Obviously in Mary Ann Lowder's case they were too effective and killed her. The name Seidlitz comes from a village in Bohemia where there is a spring who's water is impregnated with magnesium sulphate and carbon dioxide - fizzy Epsom Salts!