Heat Capacity of Silver Sulfide

The heat capacity of silver sulfide has been measured over the range 50°–400°C using an adiabatic calorimeter. The heat capacity of the $\alpha$ form, stable between 177° and about 600°C, is anomalous and has a form typical of an order–disorder transition with critical temperature at 350°C. If the sample deviates from stoichiometry by as little as one mole percent in either direction, its heat capacity is near normal at about 20 cal/mole·°C throughout the range of measurement. An interpretation of these results in terms of lattice disorder is suggested.