[Gk. Ammon, a name of Jupiter.] A chemical compound of hydrogen and nitrogen, containing three atoms of the former to one of the latter. It is an alkaline substance ; but as it differs from the other alkalies (see Alkali) in being gaseous, it is often called the volatile alkali. The gas is colorless, and has a very strong and pungent smell, by which it is easily recognized. It is found in minute quantities in the air, being evolved during the putrefaction of animal and vegetable substances. Traces of it are also found in rain-water and in the breath. Water absorbs it readily, hence ammonia is said to be very soluble in water. The solution is known to chemists as liquor arnmonicae, and in shops it is sometimes sold under the name of hartshorn. Liquor arnmoniae is sometimes used in medicine ; it has a stimulating action on the breathing, and is useful in alleviating spasms, and to some extent in counteracting the effects arising from the bites of snakes and poisonous insects. By the evaporation of liquid ammonia great cold is produced, and this fact is utilized in the manufacture of ice in ice-machines.