The method of mixtures will be used. In this method, two objects at different temperatures exchange heat. Heat from the hotter object is transferred to the colder object. In this experiment, the hotter object will be a solid of known mass. The colder object will be slightly cooled water of known mass.
Metals make good materials to measure.
As they are more dense than water, they will not float on the surface of the water, releasing some of their heat to the air. Small metal weights make good materials to investigate as their masses are known fairly accurately. The metal should be immersed in the water for several minutes. Watch the thermometer constantly, and record the highest temperature. Because water has a high specific heat capacity compared to other materials, its temperature will not rise very much.