A calorimeter is a scientific instrument used to measure the heat generated or absorbed in a chemical reaction or physical process. We owe the invention of this device to an observation made just before the turn of the nineteenth century by the preeminent scientist Benjamin Thompson ( Count Rumford). While supervising the construction of cannons, Rumford noticed that as the fire chamber was bored out, the metal cannons would heat up. He observed that the more work the drill exerted in the boring process, the greater the temperature increase. To measure the amount of heat generated by this process, Count Rumford placed the warm cannon into a tub of water and measured the increase in the water's temperature. In doing so, he simultaneously invented the science of calorimetry and the first primitive calorimeter. In simplest terms, a modern calorimeter is a water-filled insulated chamber. When a hot object is set within the water, the system's temperature increases. By measuring the increase in the calorimeter's temperature, a scientist can calculate such factors as the specific heat (the amount of heat lost per gram) of a substance.
Another application of calorimetry is the determination of the calorific value of certain fuels--that is, the amount of energy obtained when fuel is burned. Engineers burn the fuel completely within a calorimeter system and then measure the temperature increase within the device. The amount of heat generated by this burning is indicative of the fuel's calorific value.
Later scientists continued Count Rumford's work with calorimeters. During the 1860s, the French chemist Pierre Berthelot constructed a calorimeter specifically designed to measure the heat exchanged during chemical reactions, providing a wealth of insight into the nature of exothermic and endothermic reactions. At about this same time, the German physiologist Karl von Voit (1831-1908) constructed a calorimeter large enough to contain a human being. By creating a closed, measured system, Voit was able to observe the consumption of oxygen, the release of carbon dioxide, and the overall heat given off by a human body. Voit's research became the foundation for the modern understanding of human metabolism.
Calorimeters continue to be useful in modern science and in 1995 two major advances were made in calorimetery.. A Swedish company developed an ultra-sensitive microcalorimeter, also known as a Thermal Activity, which is capable measuring changes in chemical reactions down to the millionths of a watt. The device is being used by the paints and coating system to detect corrosion of metallic surfaces. The same year, the American Association for the Advancement of Science reported that a newly designed single-crystal surface calorimeter has been used to measure the energy difference between two solid surface structures. This technology could lead to exciting new discoveries in surface chemistry.
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