Hydrochloric acid is the solution of hydrogen chloride (HCl) in water. It is a highly corrosive, strong mineral acid, and therefore has major industrial use. It is found naturally in gastric acid.

Historically and colloquially called muriatic acid and spirit of salt, hydrochloric acid was produced from vitriol and common salt. The alchemist Jabir ibn Hayyan first formally decribed it in the eighth century. During the Middle Ages, it was used by alchemists in the quest for the philosopher's stone, and later by European scientists including Glauber, Priestley, and Davy in their scientific research.

With major production starting in the Industrial Revolution, hydrochloric acid is used in the chemical industry as a chemical reagent in the large-scale production of vinyl chloride for PVC plastic, and MDI/TDI for polyurethane. It has numerous smaller-scale applications, including the production of gelatin and other food additives, descaling agents and in leather processing. About 20 million metric tonnes of HCl gas are produced annually.

History

Hydrochloric acid was first discovered around 800 AD by the alchemist Jabir ibn Hayyan (Geber), by mixing common salt with sulfuric acid ("vitriol"). Jabir discovered many important chemicals, and recorded his findings in over 20 books, which carried his chemical knowledge of hydrochloric acid and other basic chemicals for hundreds of years. Jabir's invention of the gold-dissolving aqua regia, consisting of hydrochloric acid and nitric acid, was of great interest to alchemists searching for the philosopher's stone.

In the Middle Ages, hydrochloric acid was known to European alchemists as spirits of salt or acidum salis. It is still known as "Spirits of Salt" when sold for domestic cleaning purposes in the United Kingdom. Gaseous HCl was called marine acid air. The old (pre-systematic) name muriatic acid has the same origin (muriatic means "pertaining to brine or salt"), and this name is still sometimes used. Notable production was recorded by Basilius Valentinus, the alchemist-canon of the Benedictine priory Sankt Peter in Erfurt, Germany, in the fifteenth century. In the seventeenth century, Johann Rudolf Glauber from Karlstadt am Main, Germany, used sodium chloride salt and sulfuric acid for the preparation of sodium sulfate in the Mannheim process, releasing hydrogen chloride gas. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772, and in 1818 Humphry Davy of Penzance, England, proved that the chemical composition included hydrogen and chlorine.