This gives rise to dual valency states. It appears that the valence changes from about 3 to 4 when it is cooled or compressed. The low tem- perature behavior of cerium is complex. Upon cooling to - 230C, y cerium changes to fi cerium. At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point.
Cerium is an iron-gray lustrous metal.
It is malleable, and oxidizes very readily at room temperature, especially in moist air. It slowly decomposes in cold water, and rapidly in hot water. Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife. Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters, etc.