Why do eggs float by adding salt to water?

Is there any fluid dense enough to float a piece of iron or is it possible to make water dense enough to float the iron by adding salt to it?

• Answer:

  -- The density of iron near room temperature is around 7.9 gm/cc, whereas at the same temperature, mercury is liquid with a density around 13.5 gm/cc. A lump of iron will float nicely in a bowl of mercury at room temperature. -- Don't forget that aircraft carriers and battleships are also pieces of iron, and that they float nicely in water.