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Helium (He) is the second
lightest element (hydrogen being the lightest) with a gaseous specific
gravity of 0.138. It is a colorless, odorless, tasteless inert gas at room
temperature and atmospheric pressure. Its boiling point is -452.1°F
(-268.9°C) at atmospheric pressure. Helium is present in dry air at a
concentration of 0.0005%. Its principal source is natural gas wells where
the helium is extracted from the crude natural gas stream and purified.
Helium can be stored and shipped either as a gas or a cryogenic liquid.
Helium is widely used as an inert gas in the arc
welding process. Also, its low specific gravity and non flammability allow
its use in lighter-than-air applications such as the filling of balloons
and blimps. Mixtures of helium and oxygen are used as a breathing gas for
deep-sea diving. |
