Aqua (Lat. water), a favorite prefix of the old alchemists to various fluid mixtures, as aqua fortis, now called nitric acid; aqua regia, the mixture of nitric and muriatic acids, used to dissolve gold, the king of the metals, now called* nitro-muriatic acid, or nitro-chlorhydric acid; aqua vitae, now alcohol. Aquamarine is an old name given to a fine variety of beryls from the color resembling the green of sea water. - The aquae of the pharmacopoeia consist of water holding volatile or gaseous substances in solution. Those which receive a name from some volatile vegetable substance, as aqua cinnamomi or aqua campliorm, contain very much less of the active ingredient than the corresponding tinctures.