Mercury the only common metal that has a liquid form at room temperature doesn’t become a solid until it reaches -38 degrees Fahrenheit (-39 degrees Celsius). Most liquids freeze in temperatures like that. Mercury doesn’t boil until 611 degrees Fahrenheit (357 degrees Celsius), and it doesn’t stick to glass. So mercury is an ideal material to use in thermometers, which are often needed to record temperatures well below zero and well into the range where most liquids boil. (Colored alcohol is sometimes used in thermometers, but because it boils easily, it is not good for recording high temperatures.) Like all liquids, mercury expands when it is heated and contracts when it is cooled; in a thermometer it moves up and down in a closed tube on which a scale is marked, showing the temperature of the air, liquid, or solid that surrounds it. A major disadvantage to mercury is that it is extremely poisonous. Some states in the U. S. have banned the sale of mercury thermometers, and others are expected to follow. Mercury thermometers should be handled with care. If a hermometer breaks and mercury spills out, cleanup should be done by an adult wearing rubber gloves. The mercury beads should be scooped up with a piece of stiff cardboard and placed in a container with a lid. Anything that touched the mercury gloves, cardboard, container should be sealed in two layers of plastic bags. A local waste disposal agency can advise on how best to dispose of the bag containing the mercury.