FREE ESSAY ON HELIUM

HELIUM

DISCOVERY:
A French astronomer, Pierre-Jules-Cesar Janssen (1824-1907), first obtained evidence for
the existence of helium during the solar eclipse of 1868 in India when he detected a new
yellow line (587.49 nm) in the solar spectrum very close to the yellow sodium D-line. It
was not possible to produce this line in the laboratory. Sir Norman Lockyer (1836-1920),
an English astronomer, recognised that no known element at that time gave this line and
named the element helium for the sun. For many years helium was regarded as an element
that might exist on the sun although it was unknown on the Earth. Spectroscopists at the
time doubted the results concerning helium. However the claims initiated a search for the
new element on planet earth. In 1895, Sir William Ramsay discovered helium after treating
cleveite, a uranium mineral, with mineral acids. Ramsey sent samples of the gas to Sir
William Crookes and Sir Norman Lockyer who identified helium. It was discovered
independently in clevite by Cleve and Langley at about the same time. Lockyer and
Professor Edward Frankland suggested the name helium. 
USES:
-  filling balloons (blimps) as it is a much safer gas than hydrogen
-  widely used as an inert gas shield for arc welding in countries where helium is
cheaper than argon 
-  protective gas in growing silicon and germanium crystals, and in titanium and
zirconium production
-  cooling medium for nuclear reactors 
-  a mixture of 80% helium and 20% oxygen is used as an artificial atmosphere for divers
and others working under pressure 
-  cryogenic applications as a gas for supersonic wind tunnels
-  a protective gas for semiconductor materials pressurizing liquid fuel rockets
Bibliography
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