​​Why Mercury is kept in Iron Vessel?

Mercury is a reactive substance. Mercury disolves only with concentrated acids to form salts. These are used in thermometers, paint pigment, used in explosives, used in medicine (optical) & as semi-conductors just to name a few. Mercury disolves with gold, zinc & other metals to form amalgams but mercury does not react with iron that's the main reason mercury is stored in iron containers. This comes in handy for storage & transporting.