Ammonium Carbonate,also known as Baker's Ammonia or Hartshorn Salt, is a white crystal used as baking powder in Europe and as an active ingredient in some tanning processes, in smelling salts, in smokeless tobacco products and cough syrups used to treat bronchitis.
This chemical compound has been used traditionally in Scandinavian cookie recipes as a leavening agent. The cookies or biscuits that come from a recipe which uses Baker's Ammonia are characteristically very flat and have large pores. Because the compound gives off a fairly strong ammonia odor when wet, it is not used in lighter baked goods such as cakes.
Leavening agents are actually compounds made up of one or more chemicals. When the chemicals are heated, exposed to moisture or just mixed together, they react to produce gas bubbles. When these bubbles are created in cookie dough, for example, the product rises until the gasses are suddenly released, flattening the cookies and releasing a signature ammonia odor to the work area.