A calorimeter has been constructed for measuring heats of solution of salts in various solvents near room temperature and at large solvent/salt ratio. The instrument consists of a sealed tantalum vessel housing an externally driven stirrer and suspended in an evacuated submarine immersed in a constant temperature bath. The heat of stirring is compensated by a Peltier cooling device. Up to four samples of salt can be dissolved in an experiment without opening the calorimeter. A germanium resistance thermometer is used to compare the temperature change produced by the dissolving salt with that produced by electrical heating. © 1965 The American Institute of Physics.