Hartzhorn by John Spottiswood.

baker's ammonia = ammonium carbonate = carbonate of ammonia = baking ammonia = bicarbonate of ammonia = ammonium bicarbonate = powdered baking ammonia = triebsalz = hartshorn = salt of hartshorn = hirschhornsalz = hjorthornssalt = hartzhorn Originally made from the ground antlers of reindeer, this is an ancestor of modern baking powder. Northern Europeans still use it because it makes their springerle and gingerbread cookies very light and crisp. Unfortunately, it can impart an unpleasant ammonia flavor, so it's best used in cookies and pastries that are small enough to allow the ammonia odor to dissipate while baking.