We have recently been learning about life in the Stone Age. The children were particularly interested in the Stone Age method of heating liquids with hot stones. We therefore decided to try to replicate this method by attempting to raise the temperature of cold water by adding hot stones. This was much more difficult than we thought it would be! It led us to ask the questions: Why not hold  the vessel directly over the water? and How long would it take to raise the temperature of the liquid to boiling point?