The construction of an adiabatic calorimeter for the 15-300 K range is described. It is fully automated and set up in a helium refrigerator system. The operation of the calorimeter was tested by measuring the specific heat capacity of a pure copper sample. The results show good agreement with the standard literature values. The specific heat capacity of a magnesium hydride sample was also determined. For MgH2, the standard molar entropy of S-o(298.15)=30.64 J mol(-1)K(-1) was calculated from the obtained data.