A white crystalline compound, NH₄HCO₃. It is formed naturally as a decay product of nitrogenous matter and is made commercially by various methods: the action of carbon dioxide and steam on a solution of ammonium carbonate; heating commercial ammonium carbonate (which always contains some hydrogencarbonate); and the interaction of ammonia, carbon dioxide, and water vapour. It is used in some baking powders and medicines.