ammonium carbonate

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A carbonate of ammonium, (NH₄)₂CO₃.
• noun The white, crystalline double salt of ammonium bicarbonate and ammonium carbamate, (NH₄)HCO₃·NH₄CO₂NH₂, produced commercially and used in smelling salts and baking powder.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun inorganic chemistry The ammonium salt of carbonic acid, (NH4)2CO3; a white powder, smelling of ammonia, used in the preparation of smelling salts and baking powder.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a carbonate of ammonium; used in the manufacture of smelling salts and baking powder and ammonium compounds