Screw sinking in water. Gloved hand placing a brass screw into a dish of water. Brass is an alloy of copper and zinc, and is some 8.5 times denser than water. As it is more dense, it sinks to the bottom of the dish. For a repeat of the demonstration with mercury in the dish, see clip K003 3931. For the same demonstrations using a British pound coin, see clips K003 3930 mercury and K003 3935 water.