Why is there a small piece of iron sponge in my electric water boiler? My electric water boiler has a small, yet dense bit of iron sponge, about the size of a Brussels sprout. I think it is something to prevent the water from superheating. However, I'm not sure that's the only reason, because they could also just make the inside of the boiler somewhat rougher, a solution that doesn't involve a loose element hanging around in the pot that can get lost. I think there's another reason for that loose element, but I'm not sure what that reason could be. Could there be another reason beyond superheating?
They are claimed (I don't know what research has actually been done) to prevent the build-up of limescale.