Changes were performed on the apparatus of the differential reaction calorimeter (DRC) in order to get higher sensitivity. The performance of this simple instrument was tested by measuring the enthalpy of dissolution of the trihydroxymethyl aminomethane, (HOCH2)(3)CNH2, or "THAM" in 240g of 0.1 mol L-1 hydrochloric acid at 298 K. We used the joule effect to calibrate the DRC and a statistical treatment to adjust the coefficients of calibration curves. DRC was also used to achieve the dissolution of the synthesized calcium fluorapatite, Ca-10(PO4)(6)F-2, in hydrochloric acid for different concentrations at 298 K. Two solution mechanisms were suggested for different pH ranges and therefore the enthalpy of dissolution of Ca-10(PO4)(6)F-2 in pure water was deduced. (C) 2014 Elsevier B.V. All rights reserved.