Lithium, LIHTH ee uhm, is a soft, silvery-white metallic element, the lightest known metal. It is only half as heavy as an equal volume of water. It reacts with water, as does sodium, to release hydrogen gas. But, unlike sodium, the reaction usually does not ignite the hydrogen. Lithium is used to make certain types of batteries. Lithium compounds are used in the manufacture of various materials, including ceramic products, enamels, glass, and lubricants for use at high temperatures. They also are used in rubber products and in dyes for textiles. One compound, lithium carbonate, is used as a drug to treat a mental illness known as bipolar disorder, also called manic-depressive illness (see Bipolar disorder).