a. [ Cf. F. indigotique. ] (Chem.) Pertaining to, or derived from, indigo; as, indigotic acid, which is also called anilic or nitrosalicylic acid. [ 1913 Webster ]
a. (Chem.) Of, pertaining to, or designating, a sulphonic acid obtained, as a blue solution, by dissolving indigo in sulphuric acid; -- formerly called also cerulic sulphuric acid, but properly called indigo-disulphonic acid. [ 1913 Webster ]