Abstract: An apparatus for performing batchwise chemical reactions using microwave energy (10-11-12) includes a vessel (15) within a microwave cavity (13). The vessel has a sealed cover (16), located outside cavity (13), which mounts a cold-finger type heat exchanger (24) for immersion in the vessel's contents (23). Cover (16) also mounts a pressure measuring device (17) and a temperature sensing device (20) for monitoring the vessel's contents during a chemical reaction. A pressure operable safety valve (18) and a sampling facility (19) are also mounted on the cover (16). The vessel also contains a magnetically operated stirrer (22). The reactor apparatus is constructed to withstand high pressures and temperatures that may be developed within the vessel (15). Various uses of the cold-finger (24) to facilitate the conduct or completion of a chemical reaction are described.