Selecting a Calorimeter on Amazon.com
A calorimeter is an instrument for measuring the heat absorbed or released by the process of a chemical reaction or physical change. In its most basic form, a calorimeter consists of an insulated vessel that holds a sample, and a heat-measuring device for measuring the temperature before and after the process. The difference in temperature is a measure of the energy of the process. Because this differential may be small, highly sensitive thermometers, ideally those designed for calorimetry, produce the best results. For improved accuracy and consistent readings, some instruments employ a thermocouple, thermopile, or thermistor rather than a thermometer.
Calorimeters are used for testing fuel, monitoring industrial processes, determining the calorie rating of foods, and measuring chemical reactions in lab experiments and research, among other uses. They range from simple devices such as coffee cup calorimeters using two polystyrene foam cups for classroom demonstrations to complex electronic devices for scientific and food industry applications. When repeatability and documentation of results are important considerations, there are calorimeters with electronic controls and touch screen displays as well as communications ports for connecting to a printer, computer, or network.
Calorimeters are categorized as either constant pressure, in which the reaction occurs in a known volume of water, or constant volume, in which the reactants are placed in a sealed container that is then placed in water. A double-wall calorimeter is a constant pressure calorimeter with an outer vessel for insulation, an inner vessel that holds water and the substance being tested, and a lid with holes for a thermometer and a stirrer. The vessels are usually made of aluminum or copper. Some double-wall instruments have a heating coil and are used for determining the specific heat capacity and conversion energy of a material such as wood, concrete, glass, iron, or copper. For improved measurement accuracy and to measure combustion reactions, a constant volume calorimeter may be selected. Also known as bomb calorimeter, it has a reaction chamber for holding the reactants and an outer container that can be filled with water. The chamber, most often made of stainless steel, is placed in water of a known temperature, pressurized with oxygen, and, depending upon the reactants, its contents are ignited via electrical leads or other ignition circuit. Once the reaction is complete, the water temperature is measured to determine the energy generated by the process. This type of calorimeter is often used for determining the caloric content of food.