Ammonia is shipped as a liquid gas under its own vapour pressure of around 9 atmospheres. Ammonia is the oldest commercial refrigerant known and still in use today. The most extensive use is as an agricultural fertilizer. The compound is used in the form of salts, nitrates and urea.
It is the simplest stable compound of nitrogen and hydrogen and serves as a starting material for the production of many commercially important nitrogen compounds. Pure ammonia was first prepared by Joseph Priestley in 1774, and its exact composition was determined by Claude-Louis Berthollet in 1785.
Ammonia is highly soluble in water, where it forms an alkaline solution called ammonium hydroxide. Moreover, it becomes highly reactive when dissolved in water, readily combining with many chemicals. Ammonia is easily liquefied by compression or by cooling to about -33° C. Boiling of ammonia absorbs large amounts of heat and this, combined with the relatively high boiling point, makes it ideal for use in air-conditioning plant and refrigeration equipment.
Ammonia is a toxic chemical with an instantly recognisable, sharp odour. It is highly irritating to the mucous membranes and eyes. Contact with the skin causes severe burns. These are the reasons why ammonia is carefully controlled and undesirable as a result of processes.
It is not to be found in flue gas, but may be produced during anaerobic fermentation of manure and be present in the biogas formed. The corrosive nature of ammonia and the danger to health presented by this compound are the reasons that the presence of ammonia should be detected and steps taken to remove it.