Ammonium carbonate is colorless and soluble in water. It has numerous uses including smelling salts and pharmaceutical compounds.Baker’s ammonia as a leavening agent predates baking powder and baking soda, which became available in the 1850’s. Used first in Scandinavia regions to make light pastries and types of cookies. It continues in use today where required in old-fashioned recipes where crisp and light cookies etc. are wanted. Online one reads that “Icelandic air biscuits” cannot be made airy and light with anything other than ammonium carbonate. The strong ammonia smell produced during baking will dissipate when cookies are done.