<P> A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity . Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters and accelerated rate calorimeters are among the most common types . A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber . It is one of the measurement devices used in the study of thermodynamics, chemistry, and biochemistry . </P> <P> To find the enthalpy change per mole of a substance A in a reaction between two substances A and B, the substances are added to a calorimeter and the initial and final temperatures (before the reaction started and after it has finished) are noted . Multiplying the temperature change by the mass and specific heat capacities of the substances gives a value for the energy given off or absorbed during the reaction . Dividing the energy change by how many moles of A were present gives its enthalpy change of reaction . </P> <P> The name calorimeter was made up by Antoine Lavoisier . In 1780, he used a guinea pig in his experiments with this device to measure heat production . The heat from the guinea pig's respiration melted snow surrounding the calorimeter, showing that respiratory gas exchange is combustion, similar to a candle burning . </P> <P> An adiabatic calorimeter is a calorimeter used to examine a runaway reaction . Since the calorimeter runs in an adiabatic environment, any heat generated by the material sample under test causes the sample to increase in temperature, thus fuelling the reaction . </P>

When was the system of measuring calories invented