Hydrochloric acid or muriatic acid is a colorless inorganic chemical system with the formula HCl. Hydrochloric acid has a distinctive pungent smell. It is classified as strongly acidic and can attack the skin over a wide composition range, since the hydrogen chloride completely dissociates in an aqueous solution.
Hydrochloric acid is the simplest chlorine-based acid system containing water. It is a solution of hydrogen chloride and water, and a variety of other chemical species, including hydronium and chloride ions. It is a naturally-occurring component of the gastric acid produced in the digestive systems of most animal species, including humans.
Hydrochloric acid is an important chemical reagent and industrial chemical, used in the production of polyvinyl chloride for plastic. In households, diluted hydrochloric acid is often used as a descaling agent. In the food industry, hydrochloric acid is used as a food additive and in the production of gelatin. Hydrochloric acid is also used in leather processing.
Hydrochloric acid was discovered by the alchemist Jabir ibn Hayyan around the year 800 AD. It was historically called acidum salis and spirits of salt because it was produced from rock salt and "green vitriol" (Iron(II) sulfate) (by Basilius Valentinus in the 15th century) and later from the chemically similar common salt and sulfuric acid (by Johann Rudolph Glauber in the 17th century). Free hydrochloric acid was first formally described in the 16th century by Libavius. Later, it was used by chemists such as Glauber, Priestley, and Davy in their scientific research. Unless pressurized or cooled, hydrochloric acid will turn into a gas if there is around 60% or less of water. Hydrochloric acid is also known as hydronium chloride, in contrast to its anhydrous parent known as hydrogen chloride, or dry HCl.