4-((2,4-Dimethylphenyl)azo)-3-hydroxy-2,7-naphthalenedisulphonic acid, disodium salt
very slightly sol in ether, ethanol & acetone; insoluble in oil, sol in water
Masson specified a dye he called Ponceau de xylidine for a variant of his trichrome staining method. Although this dye has not been absolutely identified as the dye he used, it is almost certainly the one, and is accepted as such by general consensus. Its use is largely confined to Masson's trichrome, where it gives a slight orange shading to the red of the cytoplasmic structures.
Ponceau Xylidine has been used as part of the Goldner's trichome stain to stain thin sections. It has also been used to prepare Fuchsin-Ponceau solution to stain an amyotrophic lateral sclerosis tissue-engineered skin model (ALS-TES). Histochemical tests for proteins as xylidine Ponceau and naphthol blue–black have also been used to detect potential morphogenic regions in the explant. Cells with intense staining by xylidine Ponceau or naphthol blue–black may suggest a high incidence of RNA synthesis and high metabolic activity.