The formula on the left is from Conn. The one on the right is from Green, and illustrates the suggestion that two molecules of pyronin B are linked through ferric chloride into a larger molecule due to oxidation with ferric chloride during manufacture. This explains the difference in formula weights.
Pyronin B is sometimes substituted for pyronin Y in the Unna-Pappenheim stain for nucleic acids, but is not generally considered to be as effective for that purpose.
Compare the formula with other pyronins.
R. D. Lillie.
Conn's Biological Stains
Williams & Wilkins, Baltimore, MD., U.S.A.
Susan Budavari, Editor, (1996)
The Merck Index, Ed. 12
Merck & Co., Inc., Whitehouse Station, NJ, USA
Green, F (1990)
The Sigma-Aldrich handbook of stains, dyes and indicators
Aldrich Chemical Company, Milwaukee, Wisconsin, USA
Edward Gurr, (1971)
Synthetic dyes in biology, medicine and chemistry
Academic Press, London, England.