Rhenium is element number 75 and carries the symbol Re due to its being named after the Rhine River which is Renus in latin. A silvery-white, rare, heavy, mulit-valent transition metal, rhenium resembles manganese chemically but tungsten and molybdenum metallurgically. Rhenium is obtained as a by-product of molybdenum conversion to from molybdenite to molybdenum oxide. and rhenium-molybdenum alloys are superconducting. It was the last naturally occurring element to be discovered and belongs to the ten most expensive metals on Earth. The element is used in platinumrhenium catalysts which are used in making lead-free, high-octane gasoline. It is also used in high-temperature super alloys that are used to make jet engine parts and as an additive to tungsten in some X-ray sources.