Coin floating on elemental mercury Hg. Gloved hand placing a British one pound coin into a dish of mercury metal. Mercury is a liquid at room temperature but it still has the density of a heavy metal, being some 13.5 times denser than water. A pound coin is made of copper, zinc and nickel, and is just over half as dense as mercury. As it is less dense, it floats on the liquid metal. For a repeat of the demonstration with water, see clip K003 3935. For the same demonstrations using a brass screw, see clips K003 3931 mercury and K003 3936 water.