Argon, from argon meaning inactive, was discovered in 1894.
It was found by analyzing atmospheric gases after removing oxygen
and nitrogen. When all traces of carbon dioxide, dust, and
moisture was also removed, there was enough gas that remained such that it was
suspected that an additional gas was present. It is the most common of the noble
gases. Like the other noble gases it is colourless, odourless and tasteless.
It makes up 0.934% of the air and is released continuously by the decay of radioactive
potassium in rocks (by electron-capture of 40K).
The amounts of argon formed by radioactive decay in minerals serves as a method
to determine the age of the specimen. Shown above is the glow
discharge of argon.
Argon is used:
in filling incandescent light bulbs since the hot metallic filament tends
to evaporate if the bulb is evacuated, and it reacts if other gas is used,
in argon-arc welding for joining aluminum or stainless steel. In the presence
of air, these metals form thin layers of hard oxide which prevent the weld
from taking hold. A stream of argon flowing around the tungsten
electrode provides an inert atmosphere and protects the weld pool from oxygen
as the joint is welded.
