In such an apparatus the fuel is completely burned and the heat generated by such combustion is absorbed by water, the amount of heat being calculated from the elevation in the temperature of the water. A calorimeter which has been accepted as the best for such work is one in which the fuel is burned in a steel bomb filled with compressed oxygen. The function of the oxygen, which is ordinarily under a pressure of about 25 atmospheres, is to cause the rapid and complete combustion of the fuel sample. The fuel is ignited by means of an electric current, allowance being made for the heat produced by such current, and by the burning of the fuse wire. A calorimeter of this type which will be found to give satisfactory results is that of M. Pierre Mahler, illustrated in Fig. 24 and consisting of the following parts: A water jacket A, which maintains constant conditions outside of the calorimeter proper, and thus makes possible a more accurate computation of radiation losses. The porcelain lined steel bomb B, in which the combustion of the fuel takes place in compressed oxygen. [Illustration: Fig. 24. Mahler Bomb Calorimeter] The platinum pan C, for holding the fuel. The calorimeter proper D, surrounding the bomb and containing a definite weighed amount of water. An electrode E, connecting with the fuse wire F, for igniting the fuel placed in the pan C. A support G, for a water agitator. A thermometer I, for temperature determination of the water in the calorimeter. The thermometer is best supported by a stand independent of the calorimeter, so that it may not be moved by tremors in the parts of the calorimeter, which would render the making of readings difficult. To obtain accuracy of readings, they should be made through a telescope or eyeglass. A spring and screw device for revolving the agitator. A lever L, by the movement of which the agitator is revolved. A pressure gauge M, for noting the amount of oxygen admitted to the bomb. Between 20 and 25 atmospheres are ordinarily employed. An oxygen tank O. A battery or batteries P, the current from which heats the fuse wire used to ignite the fuel. This or a similar calorimeter is used in the determination of the heat of combustion of solid or liquid fuels. Whatever the fuel to be tested, too much importance cannot be given to the securing of an average sample. Where coal is to be tested, tests should be made from a portion of the dried and pulverized laboratory sample, the methods of obtaining which have been described. In considering the methods of calorimeter determination, the remarks applied to coal are equally applicable to any solid fuel, and such changes in methods as are necessary for liquid fuels will be self-evident from the same description.