The heats evolved in the complete combustion of many compounds in oxygen have been carefully determined. The method ordinarily used is to burn the substance in a combustion bomb and to measure the heat evolved. The heat of combustion described in this method is expressed in calories per gram of sample or British Thermal Units (Btu) per pound of sample. In the incineration process, the operating efficiency of an incinerator can be measured by energy balance techniques, and analyzing heat contents of the solid wastes before and after incineration is essential. Also the heat value is an important characteristic of solid waste needed for incinerator design. To determine directly the heat change involved in a reaction calorimeters are employed. This method describes the capabilities and limitations of a Parr Adiabatic Calorimeter, and furnishes the instructions needed to obtain best results with this apparatus.