The invention relates to a container, which is filled with a liquid medium, comprising a device for feeding gaseous substances. At least two reciprocating units are associated with the container. The reciprocating units are connected to each other by means of an energy transfer device. According to the invention it is essential that the reciprocating units each have at least one aerating device for receiving the gaseous substance from the environment of the lower region of the container and at least one height-displaceable cover element and that the bottom of the container has openings for transferring the gaseous substance into the container.
