I recently bought some Fluorinert FC-40 on eBay since it is such an intriguing chemical. This fluid is 1.8 times as dense as water, but has almost the same viscosity. It is also very inert, has a boiling point of 160*C, is immiscible with water, and has exceptionally low electrical conductivity. The fluid can dissolve large amounts of gas and was shown in the movie The Abyss where it allowed a rat (and later a human!) to breath the oxygenated fluid, by submerging the rat in a container of Fluorinert and having the rat take the fluid into its lungs.