A calculation formula for determining the specific heat capacity of solid with an improved RD496-III microcalorimeter was derived. The calorimetric constant and the relative standard deviation determined by use of Joule effect were (63.901±0.030) μV•mW^－1 and 0.08% at 298.15 K, respectively, and the total disequilibrium heat has been measured by Peltier effect. The specific heat capacities of two standard samples (benchmark benzene carboxylic acid and α-Al₂O₃) were obtained with this microcalorimeter, and differences between their calculated values and their literature ones were less than 0.4%. Accordingly, the specific heat capacities of thirteen solid complexes RE(PDC)₃(phen) (RE＝La, Pr, Nd, Sm～Lu; PDC＝ ) were also gained by the same method with their total deviations within 1.0%. These values were plotted against the atomic number of rare earth, which presents tripartite effect. It suggests existence of a certain amount of covalent character in the bond of RE^3＋and ligands, according to Nephelauxetic effect of 4f electrons of rare earth ions.

Key words: microcalorimetry, disequilibrium heat, rare earth chloride, ammonium pyrrolidinyl-N-dithio- carboxylate, o-phenanthroline, solid complex, specific heat capacity