Cobalt [gǔ][1], whose symbol element is Co, is a silver-white ferromagnetic metal. It is silver-white with light pink in the surface, located in group VIII of the fourth period in periodic table, with the atomic number of 27, the atomic weight of 58.9332, the structure of hexagonal close packing, and the common valences of +2 and +3. Cobalt is a glossy steel-grey metal, which is hard and brittle and is of ferromagnetic property, and the magnetism disappears when heated to 1150℃. The valences of cobalt are +2 and +3......