The color lakes of congo red

Abstract

Congo Red, the di-sodium salt of diphenyl-disazo-bis-mapthylamine-4-sulfonio acid, forms a free, blue acid when treated with acids and the sodium replaced by hydrogen. This is insoluble but forms a colloidal suspension of negatively charged particles* The sodium salt is a dye substantive to cotton, and likewise, the free acid will dye cotton red from its blue sol. If a positively charged hydrous oxide sol is mixed with the blue acid sol, a color lake is formed by mutual precipitation. This lake will vary in color from red thru purple to blue depending upon the hydrogen ion concentration, the temperature, and the concentrations of the sols in the mixture. Much experimentation has been done to determine whether dyeing and the formation of color lakes are adsorption phenomena rather than stoichiometrio chemical processes. It is the purpose of this paper to investigate the formation of color lakes and the action attending dyeing by Congo Red.