a heavy liquid that has a high vapor pressure at ordinary temperatures, that causes freezing when brought into contact with the skin, that is obtained by compressing anhydrous gaseous ammonia, and that is used in refrigeration and as a solvent (as in the study of ammono compounds) and as a source of gaseous ammonia.When used as a refrigerant gas and in air-conditioning equipment, ammonia can absorb substantial amounts of heat from its surroundings. Ammonia can be used to purify water supplies and as a building block in the manufacture of many products including plastics, explosives, fabrics, pesticides and dyes.