The oil of hartshorn is a crude animal oil obtained from the destructive distillation of the deers' bones or horns.
The spirit of hartshorn is an aqueous solution of ammonia. The solution was manufactured from the hooves and horns of the red deer, as well as some other animals. The aqueous solution was a colorless and pungent, consisting of about 28.5 percent ammonia gas. It was used chiefly as a detergent, for removing stains and extracting certain vegetable coloring agents, and in the manufacture of ammonium salts.
Hartshorn jelly or a decoction of burnt hartshorn in water was used to treat diarrhoea. The coal of hartshorn, called calcinated hartshorn, was used as an absorbent, as well as in the treatment of dysentery. Salt of hartshorn (ammonium carbonate) was used as a sudorific for treatment of fevers, and as a smelling salt. Hartshorn was used to treat insect bites,, sunstroke, stye, and snakebites
Hartshorn salt (ammonium carbonate), also known simply as hartshorn, and baker's ammonia, was used as a leavening agent, in the baking of cookies and other edible treats. It was used mainly in the 17th and 18th centuries as a forerunner of baking powder. ½ teaspoon of hartshorn equals to 1 teaspoon of baking powder. It is called for in old German and Scandinavian recipes and, though rarely used in modern times, may still be purchased as a baking ingredient. Use of hartshorn may turn some ingredients, such as sunflower seeds, green.
Ammonium carbonate is especially suited to thin, dry cookies. When heated it releases ammonia and carbon dioxide gases, but no water. The lack of water allows the cookies to cook and dry out faster, and thinner cookies allows the pungent ammonia to be completely baked out, rather than remaining behind, as it would in a thicker mass. Other than the pungent ammonia smell that is produced when baking with ammonium carbonate, and the possibility of an slight ammonia flavour remaining in the baking, is that the ammonia released during the baking process reacts with glucose and fructose to form intermediate molecules which in turn react with asparagine (found in nuts, seeds, and grains) to form acrylamide, a carcinogen.