Hydrochloric acid (HCL) is a colorless and highly pungent solution of hydrogen chloride and water. Once commonly referred to as muriatic acid or spirit of salt, this acid is a highly corrosive chemical compound with several applications in industry. It is also found in diluted amounts in the stomach of humans and animals as gastric acid.
This substance was first described by the 8th century Arab alchemist Jabir ibn Hayyan. In the 13th century, alchemists employed the Jabir’s theory to locate the "philosopher's stone" based on his conclusion that his discovery could turn ordinary metals into gold. Jabir’s method of combining hydrochloric acid with nitric acid, which he called aqua regia, could indeed dissolve and separate gold and silver from metal alloys and mineral ores. In fact, HCL is still used for precious metal reclamation today.
In the industry sector, hydrochloric acid is produced by dissolving hydrogen chloride in water. This process first began during the Industrial Revolution in Europe, where there was a great need to inexpensively produce soda ash on a large scale. Using a combination of limestone, sulfuric acid, and coal, salt was converted into soda ash, leaving behind hydrogen chloride as a by-product. At first, this by-product was released into the air, but under pressure of the British Alkali Act of 1863, manufacturers were forced to dissolve the hydrogen chloride in water, which produced the acid.
Today, this acid is used in great quantity to produce organic compounds, such as vinyl chloride to make polyvinyl chloride (PVC) and methylene diphenyl diisocyanate to make polyurethane. It is also used to produce bisphenol A, activated carbon, and ascorbic acid. Other uses include the manufacture of leather goods, pharmaceutical products, and various household cleaning solutions.
Important to the oil production industry, HCL is used in a process known as oil-well acidization. This process involves injecting the acid into the cavities of oil wells to dissolve away sections of rock, leaving an open column behind. Ultimately, the method serves to accelerate oil production from the well.
Extreme care must be taken when handling hydrochloric acid. In high concentrations, it releases an acid mist into the air, and both the aqueous solution and the vapor are corrosive to skin and mucous membranes. It also forms chlorine, a toxic gas, when combined with bleach or potassium permanganate. To avoid injury or irritation when working with this acid, chemical retardant clothing should be worn, in addition to PVC gloves and protective eyewear.
