Abstract: "A measurement of the heat liberated when chlorine trifluoride reacts with water has been made in a simple Dewar calorimeter. The chlorine trifluoride vapor was bubbled into approximately 20 moles of water; the weight of material used, heat equivalent of the calorimeter, and the temperature rise of the water and calorimeter were determined. From these data an average value for the heat of reaction was calculated to be 81.0 +/- 0.4 kcal/mole. Analysis of the reaction solution and evolved gas showed the following to be present: hydrogen fluoride, hydrogen chloride, chlorine, oxygen, and probably oxygen-chlorine compounds."