Thermal properties of RS(1-x)-ARS(x) studied by an ac calorimetric tec
hnique are reported. In order to obtain better values of the transitio
n entropies for the mixed crystals, two problems have remained: evalua
tion of absolute value of the specific heat and precise determination
of background of the very small anomaly. A method to evaluate the abso
lute value using the ac-calorimeter has been developed and determinati
on of the background has been improved. Finally refinement of the valu
e of the transition entropy are given for these mixed crystals.