A calorimeter is a device used for measuring the amount of heat involved in a chemical reaction or other process. In the natural gas industry, a calorimeter can be used to determine the heating value of a quantity of natural gas. 

Different methods are used by different types of gas calorimeters. Many calorimeters work on the Junker principle, which burns a known volume of gas and imparts the heat to a known volume of water to find out the rise in temperature in the water. These are called bomb calorimeters or combustion calorimeters. More recently, calorimeters that measure the thermal conductivity of a natural gas mixture at different temperatures to calculate the calorific value have come into use. Today, the use of calorimeters to determine heating value has often been displaced by use of chromatographs, which calculate the heating value by determining the chemical makeup of gas. 

A gas calorimeter