The old and still popular name for nitric acid. The article sold in the shops under this name is generally prepared by mixing common nitre with an equal weight of sulphate of iron, and half its weight of the same sulphate calcined, and distilling the mixture; or by mixing nitre with twice its weight of dry powdered clay, and distilling in a reverberatory furnace. Two kinds are found in the shops, one called double aqua fortis, which is about half the strength of nitric acid; the other simply aqua fortis, which is half the strength of the double. See Acid, Nitric