1. Also called ammonium chrome alum, ammonium chromic sulfate . a green, crystalline, water-soluble powder, chromium ammonium sulfate, CrNH 4 (SO 4 ) 2 ·12H 2 O, used chiefly as a mordant in dyeing.
2. a violet, crystalline, water-soluble powder, potassium chromium sulfate, CrK(SO 4 ) 2 ·12H 2 O, used chiefly as a mordant in dyeing.