Looks like a zinc anode. These are attached to sea going vessels. Zinc is more attractive for electrolysis in saltwater, and so will erode away first, before the steel or other metal fittings.
actually it was a cube but we cut it into two. we put ice and the uce melts approximately 3 minutes. we used a torch for 5 minutes but you can still put your hand on it immediately. we also used 22 karat gold acid but no reaction.