AQUA Regia, a compound of nitric and muriatic acid, in different proportions according to the purpose for which it is intended. It is usually made by dissolving in nitric acid, sal ammoniac, or common salt, both which are combinations of muriatic acid with alkali. When made with sal ammoniac, the common proportion is one part of this salt to four parts of nitric acid; but to dissolve platina, equal parts are requisite. A purer aqua regia may be made by simply mixing the two acids.
Aqua regia is particularly used as a menstruum for gold; it likewise dissolves all other metals, except silver. The gold dissolved in aqua regia is, in fact, dissolved in the oxygenated muriatic acid only, which gives out its oxygen to the gold, and then dissolves the oxide: for metals are not soluble in acids until they are oxidated. See CHEMISTRY Index.