9th–10th century In the early tenth century, the Persian physician and alchemist
Abu Bakr al-Razi (–925, Latin: Rhazes) conducted experiments with
sal ammoniac (
ammonium chloride) and
vitriol (hydrated
sulfates of various metals), which he
distilled together, thus producing the gas
hydrogen chloride. In doing so, al-Razi may have stumbled upon a primitive method for producing hydrochloric acid, as perhaps manifested in the following recipe from his ("The Book of Secrets"): However, it appears that in most of his experiments al-Razi disregarded the gaseous products, concentrating instead on the color changes that could be effected in the residue. According to
Robert P. Multhauf, hydrogen chloride was produced many times without clear recognition that, by dissolving it in water, hydrochloric acid may be produced.
11th–13th century Drawing on al-Razi's experiments, the ("On Alums and Salts"), an eleventh- or twelfth-century Arabic text falsely attributed to al-Razi and
translated into Latin by
Gerard of Cremona (11441187), described the heating of metals with various salts, which in the case of
mercury resulted in the production of
mercury(II) chloride (corrosive sublimate). In this process, hydrochloric acid actually started to form, but it immediately reacted with the mercury to produce corrosive sublimate. Thirteenth-century Latin alchemists, for whom the
De aluminibus et salibus was one of the main reference works, were fascinated by the chlorinating properties of corrosive sublimate, and they soon discovered that when the metals are eliminated from the process of heating vitriols,
alums, and salts, strong
mineral acids can directly be distilled.
14th–15th century Aqua regia One important invention that resulted from the discovery of the mineral acids is
aqua regia, a mixture of
nitric acid and hydrochloric acid in a 1:3 proportion, capable of dissolving gold. This was first described in
pseudo-Geber's
De inventione veritatis ("On the Discovery of Truth", after ), where
aqua regia was prepared by adding ammonium chloride to nitric acid. The fact that
aqua regia typically is defined as a mixture of nitric acid and hydrochloric acid does not mean that hydrochloric acid was discovered before or simultaneously with
aqua regia. The isolation of hydrochloric acid happened about 300 years later. The production of hydrochloric acid itself (i.e., as an isolated substance rather than as already mixed with nitric acid) depended on the use of more efficient cooling apparatus, which would only develop in subsequent centuries.
16th–17th century From the point of view of Western history of chemistry, hydrochloric acid was the last of the three well-known mineral acids for which the method of its production appeared in the literature. Recipes for its production started to appear in the late sixteenth century. The earliest recipes for the production of hydrochloric acid are found in
Giovanni Battista Della Porta's (1535–1615)
Magiae naturalis ("Natural Magic") and in the works of other contemporary chemists like
Andreas Libavius (–1616),
Jean Beguin (1550–1620), and
Oswald Croll (–1609). Among the historians who have written about this are German chemists
Hermann Franz Moritz Kopp (1845) and
Edmund Oscar von Lippmann (1938), mining engineer (and future U.S. president)
Herbert Hoover with his wife geologist
Lou Henry Hoover (1912), Dutch chemist
Robert Jacobus Forbes (1948), American chemist
Mary Elvira Weeks (1956), and British chemists
F. Sherwood Taylor (1957) and
J. R. Partington (1960). Italian chemist Ladislao Reti summarized the result of their efforts thus:
Dissolving metals The knowledge of mineral acids such as hydrochloric acid would be of key importance to seventeenth-century chemists like
Daniel Sennert (1572–1637) and
Robert Boyle (1627–1691), who used their capability to rapidly dissolve metals in their demonstrations of the composite nature of bodies.
Industrial developments During the
Industrial Revolution in Europe, demand for
alkaline substances increased. A new industrial process developed by
Nicolas Leblanc of
Issoudun, France enabled inexpensive large-scale production of
sodium carbonate (soda ash). In this
Leblanc process, common salt is converted to soda ash, using sulfuric acid, limestone, and coal, releasing hydrogen chloride as a by-product. Until the British
Alkali Act 1863 and similar legislation in other countries, the excess HCl was often vented into the air. An early exception was the
Bonnington Chemical Works, where, in 1830, the HCl began to be captured and the hydrochloric acid produced was used in making sal ammoniac (
ammonium chloride). After the passage of the act, soda ash producers were obliged to absorb the waste gas in water, producing hydrochloric acid on an industrial scale. In the 20th century, the Leblanc process was effectively replaced by the
Solvay process without a hydrochloric acid by-product. Since hydrochloric acid was already fully settled as an important chemical in numerous applications, the commercial interest initiated other production methods, some of which are still used today. Since 2000, hydrochloric acid is mostly made by absorbing by-product hydrogen chloride from
industrial organic compounds production. ==Chemical properties==