Mercury exists as a liquid at room temperature. This is one of the "cool" physical properties of mercury, as it is classified as a metal. Mercury, being a liquid at room temperature, is an excellent comparison to water when studying density, as mercury is 13.6 times more dense than water. Since it is in a liquid state at room temperature, mercury is used in thermometers, barometers, and hygrometers. Care should be taken not to touch mercury, as it is poisionous and can be absorbed directly through the skin.