Screw floating on elemental mercury Hg. Gloved hand placing a brass screw 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. Brass is an alloy of copper and zinc, and is around 8.5 times denser than water. As it is less dense than mercury, it floats on the liquid metal. For a repeat of the demonstration with water, see clip K003/3936. For the same demonstrations using a British pound coin, see clips K003/3930 mercury and K003/3935 water.