S 1905 (OTTO) Sodium dithionite Cas 7775-14-6 - used as a reducing agent in aqueous solutions. S 1905 (OTTO) Sodium dithionite Cas 7775-14-6 - used as such in some industrial dyeing processes, primarily those involving sulfur dyes and vat dyes, where an otherwise water-insoluble dye can be reduced into a water-soluble alkali metal salt (e.g. indigo dye)