Abstract: Apparatus for generating and storing under pressure vaporized reactants consisting of a heat exchanger in fluid communication with an expansion chamber comprising a lower header and an upper header. At least one duct extends between the lower and upper headers for communication therebetween. A collection vessel communicates with the upper header by means of at least one riser.Heat exchange fluid is heated to operating temperature and circulated through the lower header to the upper header and returned to the heat exchanger. A reactant is introduced into the heat exchange medium and is vaporized thereby. The vapors are confined in heat exchange medium and circulated to the expansion chamber where the vapors escape from the heat exchange medium. The vapors are led by the riser to the collection vessel where they are stored under pressure at sufficient temperature to prevent condensation.