A leavening agent also known as baker’s ammonia or hartshorn, prized for producing exceptionally crisp, light textures in low-moisture baked goods such as crackers, cookies, and Scandinavian biscuits. When heated, it decomposes completely into ammonia, carbon dioxide, and water vapor, all gases that leaven the dough and then escape, leaving no alkaline residue or soapy aftertaste. This clean breakdown is its advantage over baking soda in thin products, but the escaping ammonia would be trapped unpleasantly in moist, thick items, so its use is limited to goods dry enough to let the gas vent fully. Traditional recipes call for it by its old names, and it remains irreplaceable for the snap and openness of certain heritage biscuits.