Benzoic acid, 5-[[4-[(2,4-dihydroxyphenyl)azo]-3-sulfophenyl]azo]-2-hydroxy-, disodium salt

3-(4-Amino-2-sulfophenylamino)-2,3-dioxopropanoic acid diazo, coupled with 2-Hydroxybenzoic acid, grass acid base hydrolysis, again diazo, Coupled with resorcinol.

dark red to red light brown. Soluble in water for orange brown, slightly soluble in alcohol. The strong sulfuric acid for purple, diluted shallow orange for brown. The dye solution to join strong hydrochloric acid have orange brown precipitation; Add thick sodium hydroxide solution for dark purple.