The Collaborative International Dictionary of English v.0.48:

Murexide \Mu*rex"ide\, n. [L. murex the purple fish, purple.]
   (Chem.)
   A crystalline nitrogenous substance (C8H8N6O6,
   5-5'-nitrilodibarbituric acid monoammonium salt) 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. It is now synthesized from alloxan. Formerly called
   also ammonium purpurate.
   [1913 Webster +PJC]