Argon (Ar) is two and one half times as soluble in water as nitrogen, having about the same solubility as oxygen. It is colorless and odorless, both as a gas and liquid. Argon is considered to be a very inert gas and is not known to form true chemical compounds, as do krypton, xenon, and radon.
Cavendish suspected argon’s presence in air in 1785, discovered by Lord Raleigh and Sir William Ramsay in 1894.
The gas is prepared by fractionation of liquid air because the atmosphere contains 0.94% argon. The atmosphere of Mars contains 1.6% of Ar and 5 p.p.m. of Ar.
Naturally occurring argon is a mixture of three isotopes. Twelve other radioactive isotopes are known to exist.
It is used in electric light bulbs and in fluorescent tubes at a pressure of about 400 Pa. and in filling photo tubes, glow tubes, etc. Argon is also used as an inert gas shield for arc welding and cutting, as a blanket for the production of titanium and other reactive elements, and as a protective atmosphere for growing silicon and germanium crystals.