Sulphindigotic /(?)/

Sulph·in·di·got·ic

Sulphindigotic

a.
  1. 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. (Chem.)