Rubidium

It's in vacuum tubes.



    Rubidium is used in vacuum tubes as a getter, a material that combines with and removes trace gases from vacuum tubes. It is also used in the manufacture of photocells and in special glasses. Since it is easily ionized, it might be used as a propellant in ion engines on spacecraft.

    Rubidium is also in finger nail polishes.

    Rubidium is also in fire works .