With the help of an activity show that water is a bad conductor of heat?

Take a boiling tube of water, add an ice cube, and place a weight on top, so it sinks to the bottom. Clamp the tube and heat the top with a Bunsen burner. In a very short time, the water at the top will boil, whereas the ice cube remains at the bottom. Despite a temperature difference of 100�, the ice does not melt, meaning no heat is transferred. Therefore, water is a very poor heat conductor.