murexide
Mu*rex"ide, n. Etym: [L. murex the purple fish, purple.] (Chem.) Defn: A crystalline nitrogenous substance having a splendid dichroism, being green by reflected light and garnet-red by transmitted light. It was formerly used in dyeing calico, and was obtained in a large quantities from guano. Formerly called also ammonium purpurate.