Why Does Iron Sink in Water?
The explanation in regard to the piece of wood floating in water is the beginning of the answer to this question. A piece of iron is heavier than an equal bulk of water, and will therefore go to the bottom, as will all things which are more dense than water. A piece of iron has no air in it. The particles of a piece of iron are so close together that there is no room for air in it and it will therefore sink in water. A piece of wood from which all of the air had been expelled would also sink.