The greatest use of hydrogen is in the production of ammonia by the Haber process, and in the hydrogenation of fats and oils. Vegetable oil is converted to margarine by this process. It is also used in the refining of petroleum, the reduction of oxide ores to metals, and the production of hydrocarbons from coal.
Because of its usefulness as a rocket fuel, large quantities of hydrogen are used in the United States space programme. Tritium, one of its isotopes, is used in the production of luminous paints and of the hydrogen bomb.
Being the lightest of all gases, hydrogen was once used to inflate dirigible balloons, but its high inflammability led to a number of explosions and its eventual replacement by helium.
