The bath (4) is arranged the supply reservoir (5) for the liquid (3), in which the reaction flask to be heated or cooled can be immersed. The heating or cooling device (8) is arranged on the bottom of the supply reservoir (5). The liquid (3) is delivered with an immersion pump (19) through a feed pipe (6) and an opening (18) in the bottom of the bath (4). The level of the liquid in the bath (4) can be adjusted with the aid of a slider (11). The liquid flows back into the supply reservoir (5) over an overflow (7). When the pump (19) is switched off, the liquid (3) in the bath (4) flows independently back into the supply reservoir (5).