Abstract: The invention provides a novel method for the storage and recovery of thel energy by utilizing a medium substance for the storage of heat. The medium substance is a liquid complex of sodium iodide and ammonia, which absorbs heat as latent heat when brought under a reduced partial pressure of ammonia to effect liberation of ammonia and releases the thermal energy as sensible heat when brought under an increased partial pressure of ammonia to absorb ammonia. Different from conventional solid medium substances for storage of heat, the liquid medium proposed is very convenient in handling so that a chemical heat pump with simple structure can be contrived by use of the inventive method.