A new type of calorimeter was designed and was tested on the reaction enthalpy of TRIS in 0.1 mol/cm3 HCl. The DHTRIS obtained is -245.41 J/g ?0.24, which is in good agreement with the value recommended by IUPAC in 1976. Integral heats of solution of RECl3.3H2O (RE + La, Ce, Nd, sm, Eu, Gd, Tb, Dy, Erb, Yb, Y) in water at 298.15 K and final concentration = 0.01541 mol/kg anhydrous salt) were determine The standard enthalpies of formation and of dehydration (RECl3.3H2O甊ECl3) of some of these hydrates were calculated and discussed.

Key words: THERMAL ANALYSIS, LANTHANUM COMPOUNDS, CHLORIDE, HYDRATE, ENTHALPY OF FORMATION, EUROPIUM COMPOUNDS, CERIUM COMPOUNDS, THERMOCHEMISTRY, RARE EARTH COMPOUNDS, ERBIUM COMPOUNDS