Алхимиядағы әмбебап еріткіш – алкагест тұңғырығы

Theorized universal solvent in alchemy

In Renaissance alchemy, alkahest was the theorized "universal solvent". It was supposed to be capable of dissolving any composite substance, including gold (then not considered an element), without altering or destroying its fundamental components. By extracting from composite substances their fundamental virtues and properties, alchemists hoped to gain control of invaluable medical healing properties (see also azoth). For this reason the alkahest was earnestly sought. At the same time, its very existence was debated among alchemists and philosophers. The first, or one of the first, to mention the alkahest was the Swiss physician and alchemist Paracelsus.

There is no consensus on the origin and etymology of the word alkahest, as Paracelsus left no trace or history of the word. George Starkey argued it came from the German word al gehest (all spirit). Johann Rudolph Glauber posed that it could have come from the words alhali est, the German word al gar heis, or Al zu hees, meaning "very hot". He also used the term "maccabean fire" because of its similarities to the "thick water" in the deuterocanonical Book of Maccabees in the Old Testament. Paracelsus's own recipe for alkahest was made of caustic lime, alcohol, and carbonate of potash; however, his recipe was not intended to be a "universal solvent".

Alkahest became very popular in the 17th and 18th centuries through Jan Baptist van Helmont. Its prevalence in the 17th and 18th centuries, despite its otherwise absurd and extreme qualities, was likely due to the popularity of alchemy at the time and the lack of an adequate alternative theory of chemistry.

Colonial American alchemist George Starkey (1628–1665) described alkahest as a circulated salt that is neither acid nor alkali. According to Helmont and Anglo Irish scientist Robert Boyle (1627–1691), the alkahest had a "microstructure", meaning it was composed of extremely small, homogeneous corpuscles. hence, a hypothetical container made of a pure element (say, lead) would not be dissolved by alkahest.

Paracelsus believed that alkahest was, in fact, the philosopher's stone. Dutch chemist and physician Herman Boerhaave (1668–1738), in his textbook Elementa Chymiae (1732), did not think alkahest was the philosopher's stone, but of greater importance and value than the stone. "Alkahestry" is the term used for a type of alchemy in the manga Fullmetal Alchemist.