Description Methylene Blue It’s a formal derivative of phenothiazine and is used in the management and treatment of methemoglobinemia. For more information read: Methylene blue on Science Daily CAS Number 7220-79-3 Appearance Liquid Chemical Names 3,7-bis(Dimethylamino)-phenothiazin-5-ium chloride Molecular Formula C16H18CIN3S.3H2O Molecular Weight 319.85 g/mol