This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Acid gathers five corrosive liquids from the alchemical workshop, three of them the classic strong mineral acids and two of them milder substances that still belong in the same working category. Aqua Fortis, Aqua Regia and Oil of Vitriol are the strong trio: Aqua Fortis dissolves silver readily while leaving gold untouched, which made it the standard laboratory test for separating the two metals, while Aqua Regia, made by combining Aqua Fortis with Spirit of Salt or common salt, was prized as the one liquid able to dissolve gold itself. Oil of Vitriol, distilled from roasted green vitriol, was thought of as the concentrated acid spirit locked inside vitriol salts and eventually became one of the first chemicals manufactured at industrial scale. Spirit of Salt, the third mineral acid, was less dramatic than the other two but valued for precipitating silver from solution as an insoluble white curd.
Vinegar is the group's clear outlier, a mild acid known from the kitchen rather than the laboratory bench, used where the mineral acids were too aggressive, notably in preparing verdigris from copper. What holds the group together despite that range of strength is a shared identity in modern chemistry: every member maps cleanly onto a known acid, nitric for Aqua Fortis, a nitric and hydrochloric mixture for Aqua Regia, sulfuric for Oil of Vitriol, hydrochloric for Spirit of Salt, and dilute acetic for Vinegar, making Acid one of the more chemically unambiguous groupings this taxonomy holds.