Ammonia is a colorless gas with a very strong smell. Large quantities are poisonous, but smaller doses will cure faintness. Smelling salts give off small amounts of the gas, which is about three-fifths the weight of air. When it is compressed and cooled, it is easily changed from a gas into a colorless liquid which looks very much like water, but which boils at a temperature of -33° Centigrade. When the pressure is lessened the liquid vaporizes again, absorbing heat. For this reason ammonia is of great use in ice making and in refrigerators. You can read more about this in the article refrigerators.
Ammonia dissolves very easily in water and forms an alkaline solution of ammonium hydroxide. This solution turns red litmus blue and will react with acids to form ammonium salts. Household ammonia, which is used to soften hard water for cleaning and washing, and also "aqua ammoniac", are weak solutions of ammonia in water.
Some ammonia is found in the air and comes from decaying plants and animals; the smell of burning feathers, leather or fur is partly due to the ammonia gas given off. Very small quantities of it are sometimes found in rain water.
Ammonium compounds have been known for hundreds of years. They were called this because ammonium chloride, or sal ammoniac, was first found near the Temple of Jupiter Ammon in Egypt. Ammonia was once called spirits of hartshorn because it was made from the horns, hoofs and hide of the hart or male deer. Joseph Priestley, an English chemist, first made the pure gas in 1774, naming it "alkaline air".
Ammonia is composed of the elements of nitrogen and hydrogen. In industry the method chiefly used for making ammonia is to combine these two gases. The nitrogen is obtained from the air and the hydrogen from water. The two gases are dried, compressed and heated to a temperature of about 500° Centigrade; they are then passed over a mixture of iron powder with various salts and a certain amount of the gases combine to form ammonia. This is called the Haber process and was developed during World War I in Germany, when that country was desperately in need of nitrogen compounds from which to make explosives.
Large quantities of ammonia can also be obtained as a by-product from the making of coal gas and coke, although this is not such a pure form of the gas. For small quantities of ammonia, to be used in a laboratory, any ammonium salt can be treated with slaked lime or another alkali.
The Uses of Ammonia
When ammonia comes into contact with acids it forms ammonium salts. Smoke screens used by battleships in World War I to hide them from submarines were sometimes made by allowing ammonia gas to escape from cylinders of liquid ammonia and mingle with acid vapors to form a dense cloud round the ship. Better screens had been discovered by World War II so ammonia was no longer used.
Many ammonium salts are useful. Ammonium chloride, or sal ammoniac, is used in soldering, in electric batteries and in medicine. Ammonium nitrate is used in making some explosives, and ammonium sulphate has a most important use as a fertilizer. It is important for the growth of plants that the soil contains much nitrogen. It can obtain this from ammonium sulphate, which is made from ammonia gas. Bottles of "smelling salts" contain ammonium carbonate which, on opening, give off ammonia gas. Ammonium carbonate is also called sal volatile. All these salts are made by treating ammonia with the right acid. Ammonium salts are also formed naturally and are found in fertile soil, in volcanic areas, in sea water and in rotting plants and animals.