A bad experimental set-up! The temperature of the hot metal is impossible to determine directly with a thermometer. Therefore, a test tube of the metal is immersed in boiling water for ten minutes, and we assume that the temperature of the metal is then the same as that of the boiling water. The temp of the boiling water is then easily measured with a thermometer. However, all of the metal must be below the water line for our assumption to be valid.