VI.

Discovery of Hydrogen

Early chemists confused hydrogen with other gases until British physicist and chemist Henry Cavendish described the properties of hydrogen gas in the mid-1700s. Many scientists before Cavendish had made the flammable gas by mixing metals with acids. Cavendish called the gas flammable air and studied it. He demonstrated in 1766 that sulfuric acid reacted with metals to produce flammable air. Later, Cavendish burned his flammable air in regular air to produce water, and only water. Many historians consider Cavendish to be the principle discoverer of hydrogen gas, although Scottish engineer James Watt reported that he had produced water at about the same time as Cavendish.

The isotopes deuterium and tritium were discovered in the 20th century. Shortly after World War I (1914-1918), British physicist Francis W. Aston invented a mass spectrograph (see Mass Spectrometer), a device that separates atoms by their masses. He found atoms with masses that were unusual, namely the isotopes. This provided the first clue to the existence of deuterium. In 1932 American chemist Harold C. Urey and his associates isolated and discovered deuterium. Urey predicted that water made with deuterium would evaporate more slowly than would water made with protium and was, in this way, able to separate and isolate the deuterium. Scientists first produced tritium in 1935 by bombarding deuterium with deuterium nuclei (one proton and one neutron). Scientists have since found tritium in very small amounts in ordinary water. Tritium forms naturally in some atmospheric reactions.