An isothermally jacketed liquid calorimeter permitting thermochemical studies on spontaneous combustion in fluorine has been built and tested. The fluorine storage tank was located outside the calorimeter vessel, thus lowering the heat capacity of the system and its thermal inertia. Particular attention was paid to the method and rate of liquid circulation since it largely determines the experimental accuracy. The system can be calibrated electrically. The possible experimental errors are discussed, and their analysis shows that calibration is feasible with an accuracy of ≳99.98%. A series of measurements involving a temperature rise of about 0.9 K showed a standard deviation of 0.02%.