*nitroprussic*

a. [ Nitro- + prussic. ] (Chem.) Pertaining to, derived from, or designating, a complex acid called nitroprussic acid, obtained indirectly by the action of nitric acid on potassium ferrocyanide (yellow prussiate), as a red crystalline unstable substance. It forms salts called nitroprussides, which give a rich purple color with alkaline sulphides. [ 1913 Webster ]