Meaning of chrome alum

chrome' al"um

Pronunciation: [key]
  1. Also calleda green, crystalline, water-soluble powder, chromium ammonium sulfate, CrNH(SO)&multiplydot;12HO, used chiefly as a mordant in dyeing.
  2. a violet, crystalline, water-soluble powder, potassium chromium sulfate, CrK(SO)&multiplydot;12HO, used chiefly as a mordant in dyeing.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.