What is helium?

   Helium is a colorless, non-inflammable gas whose practical value was demonstrated in 1918, when American chemists discovered a method of producing it in quantity. Helium like nitrogen and argon, has prac¬tically no chemical activity. It is twice as heavy as hydrogen, the lightest known substance, and is now used in place of that gas for inflating balloons because it will not take fire. Helium is found in the atmos¬phere in proportion of 4 volumes of the element to 1,000,000 volumes of air. It is generally obtained from liquid air by distillation, but it can be separated from its compounds by the use of nitrogen or argon. It occurs in some minerals and is thought to be a product of the disintegration of radium.

Helium atom