History
Krypton was discovered in Britain in 1878 by Sir William Ramsay, a Scottish chemist, and Morris Travers, an English chemist, in residue left from evaporating nearly all components of liquid air. Neon was discovered by a similar procedure by the same workers just a few weeks later. William Ramsay was awarded the 1904 Nobel Prize in Chemistry for discovery of a series of noble gases, including krypton.
In 1970, an international agreement defined the meter in terms of wavelength of light emitted by the krypton-86 isotope (wavelength of 605.78 nanometers). This agreement replaced the longstanding standard meter located in Paris, which was a metal bar made of a platinum-iridium alloy (the bar was originally estimated to be one ten-millionth of a quadrant of the Earth's polar circumference), and was itself replaced by a definition based on the speed of light — a fundamental physical constant. However, in 1927, the International Conference on Weights and Measures had redefined the meter in terms of a red cadmium spectral line (1 m = 1,553,164.13 wavelengths). In October 1983, the same bureau defined the meter as the distance that light travels in a vacuum during 1/299,792,458 s.
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