A relatively simple adiabatic calorimeter has been developed for measuring the thermal properties of 0.5‐g samples of stable liquids or fusible solids over the temperature range of −130° to +200°C. Adiabatic conditions are automatically maintained during a run by means of a control system based on the use of resistance thermometers and a modified commercial electronic thermoregulator. Fifteen determinations on four pure compounds show that the heat of fusion can be determined to an accuracy of about 1%. Because of the simple semi‐automatic operation, the apparatus is particularly suited to the determination of the purity of organic compounds by the calorimetric method.