It is a vessel to measure the amount of heat gained or lost by a body when mixed with another body. It is made up of thin sheet of copper as it is a good conductor of heat and it has a low specific heat capacity so it can acquire the temperature of its contents with little amount of heat. To avoid heat loss through radiation the inner side is polished. To avoid heat loss through conduction it is insulated with wood and the space between the wood and the copper is a poor conductor. To avoid heat loss through convection a wood lid is placed on the top. The lid has two holes, one for the thermometer and the other for the stirrer.