A calorimeter is an instrument for measuring calorimetry, the science of measuring the heat of chemical reactions or physical changes. Calorimeters can be defined as the following types; reaction calorimeters, heat flow calorimeters, heat balance calorimeters, bomb calorimeters, constant-pressure calorimeters, differential scanning calorimeters, isothermal titration calorimeters, X-ray microcalorimeters, heat-loss calorimeters and high-energy particle calorimeters..