Denser than Air

[ExoByte]

I saw this on Jay Leno's show, and as well on a YouTube video of some students doing this experiment. Basically, its like an "Anti Helium." Its an invisible gas that is so heavy that it does not rise. So if you were to fill a tank with it, it would stay in the tank. They demonstrated this by placing an aluminum boat on a tank filled with the gas, and it floated there with nothing supporting it. It was like invisible water. When breathed in, rather than making your voice higher like helium, it made the voice much deeper. Heres a link to the it on Jay Leno.(YouTube) Click Does anyone know the name of this chemical/element? I'm actually quite interested. EDIT: I think its called Sulfur Hexafluoride, based on the related video names :p