Helium


The discovery of helium was made in radioactive materials and for a while the element was thought to be very rare. However, a few years later, it was proved to be present both in the earth's crust and atmosphere. Accordingly to Ramsay, the atmosphere near the Earth contains 0.0004% of hellium (in number of molecules) i.e one hellium molecule per 200000 air constituents molecules.

Helium was also found very low quantities in rocks, natural and vulcanic gases and radioactive minerals.