AQUA regia, an acid corrosive spirit, so called, because it serves as a menstruum to dissolve gold, commonly esteemed the king of metals. Its basis, or essential ingredient, is common sea-salt, the only salt in nature which will operate on gold. It is commonly prepared by mixing common sea-salt, or sal ammoniac, or the spirit of them, with spirit of nitre, or common aqua fortis. See CHEMISTRY, title, Of aqua regia.