An automatic temperature control device for an adiabatic oxygen bomb calorimeter has been developed which keeps the temperature of the outer water jacket equal to that of the inner bath. When the temperature of the inner bath is not changing rapidly, heat losses are negligible; however, the error due to lag when the inner bath temperature is rising rapidly is about two parts per thousand. This degree of precision permits the accurate analysis of samples of low caloric content such as lyophilized urine. Since the technician need not watch the calorimeter once the bomb has been fired, but instead can prepare a second bomb, the number of samples analyzed in a given time can be doubled if two bombs are available for use with the calorimeter.