Radioactive dating using potassium argon

Argon is the third-most abundant gas in the Earth's atmosphere, at 0.934% (9340 ppmv).

The inner platinum ends (DD) of the wire receive a current from a battery of five Grove cells and a Ruhmkorff coil of medium size.

An unreactive gas was suspected to be a component of air by Henry Cavendish in 1785.

The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements.

Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990.

This discovery caused the recognition that argon could form weakly bound compounds, even though it was not the first.

Argon-36, in the form of argon hydride (argonium) ions, has been detected in interstellar medium associated with the Crab Nebula supernova; this was the first noble-gas molecule detected in outer space.

Argon is produced industrially by the fractional distillation of liquid air.

Argon is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily unreactive substances become reactive; for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature.

Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water, and nitrogen from a sample of clean air.

They had determined that nitrogen produced from chemical compounds was 0.5% lighter than nitrogen from the atmosphere.

Mendeleev positioned the elements on his periodic table in order of atomic weight, but the inertness of argon suggested a placement before the reactive alkali metal.

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