So where the heck does 58 come from?
Cerium /ˈsɪəriəm/ is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet Ceres
the dwarf planet discovered on 1/1/1801
he reffered to the date as beeing a periodic apearance which was the clue really.
i usually dont bother with these as someone has usually done them by time you work it out anyway im amazed no one else already got it, i was going to have a go this morning but decided someone probably had got it and never said anyway