Sulphindigotic \Sulph*in`di*got"ic\, 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]