Krypton is a gaseous chemical element that exists in concentrations of about one part per million in the Earth's atmosphere. Since it exists in low concentrations, it is difficult and expensive to extract, making it rather expensive when it reaches the market. Its most common use is in lighting, since the gas glows a very bright white when it conducts current. Many so-called “neon” signs are actually made with krypton in colored tubes that glow as the gas turns into plasma.
The groundwork for finding krypton was laid in 1785, when Henry Cavendish observed that the air contained a fraction that was neither oxygen nor nitrogen. It turns out that several elements that came to be known as the noble gases were present in this fraction, and scientists began to identify these gases one by one. Krypton was discovered in 1898 by William Ramsay and Morris Travers, along with neon and xenon.
Like many noble gases, krypton is odorless, colorless, and tasteless. When it is solidified, it creates cubed white crystals, and its spectral signature is a rich green to red. The element has an atomic number of 36, and it is identified with the symbol Kr on the periodic table. The gas itself is relatively stable and nonreactive, although radioactive isotopes can be created through nuclear reactions. The bulk of the element in the environment is found in the atmosphere, although it also appears in minerals and meteorites.
To extract krypton, scientists must use a process called fractional distillation. In this process, a sample of the air is cooled so that it solidifies, and then it is gently heated so that it reverts to a gaseous form. Because the elements in the air become gaseous at different temperatures, they will precipitate out at different rates, allowing scientists to collect them in the air one by one as they revert to a gaseous state. Fluorescent lights often use krypton, as do extremely bright lights that may use a mixture of noble gases to function.
There are a few pieces of trivia which make krypton a particularly interesting element for some people. It very briefly served as the official definition for the length of a meter, which was determined on the basis of the spectral length of one isotope of the element. It also lends its name to the fictional planet Krypton, home of Superman and the dangerous mineral kryptonite. Unlike kryptonite, however, this element is not very hazardous to life, although it can act as an asphyxiant in high concentrations by displacing the oxygen which most organisms need to breathe.