The heat capacities of Pd4S and Pd4Se were determined by adiabatic calorimetry from 5°to 350°K. and found to be of usual sigmate shape, without transitions or anomalies. Values of the heat capacity (Cp), entropy (S°), and Gibbs energy function [ -(G°-H°)/T] at 298.15°K. (expressed in units of cal. mole"1 °K._1) are 27.48, 43.18, and 23.16 for Pd4S and 32.75, 47.83, and 24.84 for Pd4Se, respectively. The heat capacity of Pd4Se exceeds the classical limit near 200°K ., probably because of 4d-electron excitations in palladium.PALLADIUM is apparently the only metal which forms a sulfide and a selenide in the atomic ratio of 4 to 1 (4, 5). Therefore, it seemed of interest to study the thermodynamic properties of these rather unusual compounds. The structures of Pd4S and Pd4Se are tetragonal (4, 5) and characterized by coordination of each palladium atom with two sulfur (selenium) atoms and ten palladium atoms, while each sulfur (selenium) atom is coordinated to eight palladium atoms. Above 150°C. the compounds are almost nonmagnetic (xe<0.2 x 10"6), but upon lowering the temperature, field-strength-dependent magnetic susceptibilities develop. This phenomenon apparently needed further consideration; hence, heat capacity measurements were undertaken. EXPERIMENTAL Cryogenic Apparatus. Measurements were made in the Mark III vacuum cryostat by heating the sample intermittently under quasi-adiabatic conditions. The goldplated copper calorimeter (laboratory designation W-29), with a capacity of 41 cc., was surrounded by adiabatic shields provided with three separate channels of recording electronic circuitry with proportional, rate, and reset actions. These kept the temperature differences between calorimeter and shields less than a millidegree. Consequently, the error due to heat exchange was negligible compared with other sources of error. The heat capacity of the calorimeter-heater-thermometer assembly was determined in a separate series of experiments. Small corrections were applied for differences in the amounts of indiumtin solder for sealing the calorimeter, Apiezon-T grease for thermal contact between calorimeter and heaterthermometer assembly, and about 10-torr helium pressure at 300°K. for improving thermal equilibration between calorimeter and sample. Temperatures determined with the strain-free capsule-type platinum resistor (laboratory designation A-3) are considered to be in accord with the thermodynamic temperature scale to within 0.03°K. All measurements of mass, temperature, resistance, voltage, and time are based upon calibrations or standardizations of the National Bureau of Standards.