Instruments used to measure the amount of energy in a sample by measuring the amount of heat released or absorbed during combustion; available in portable and benchtop configurations. When two bodies of different temperatures (preferably a solid and a liquid) are placed in physical contact with each other, the heat is transferred from the body with a higher temperature to the body with a lower temperature until thermal equilibrium is attained between them. The body at higher temperature releases heat while the body at lower temperature absorbs heat. The principle of calorimetry indicates the law of conservation energy, i.e. the total heat lost by the hot body is equal to the total heat gained by the cold body. Heat Lost = Heat Gained