Mercury is named from the planet Mercury, the symbol is derived from the Latin hydrargyrum, liquid silver. Mercury was known to the ancients and has been found in Egyptian tombs from 1500 b.c. Mercury is the only common metal liquid at room temperatures. It only rarely occurs free in nature. The chief ore is cinnabar and Spain and Italy produce about 50% of the world's supply of the metal. The metal is obtained by heating cinnabar in a current of air and condensing the vapor. It is a heavy, silvery-white metal that is a poor conductor of heat, but a good conductor of electricity. It easily forms alloys with many metals, such as gold, silver and tin, which are called amalgams. The metal is widely used in making thermometers, barometers, diffusion pumps and many other instruments. It is used in making mercury-vapor lamps and advertising signs, and is used for mercury switches and other electrical apparatus.