A bis(azo) compound that is 1,1'-(1,3-phenylene)bis(diazene) in which both azene hydrogens are replaced by 2,4-diaminophenyl groups. A metachromatic dye which stains acid mucins yellow. It is also a constituent of Papanicolaou's EA solutions, used for cervical, and other smears. Its dihydrochloride salt is also a biological dye known as Bismark brown Y.