An insert for insertion into a pressurized container for liquids has a component chamber for receiving an active substance and a pressure chamber for introducing the active substance into the liquid when opening the container for liquids. The pressure chamber has at least one small outer bore. The insert is freely movable in the container for liquids but has such a stable floating position on a surface of the liquid within the container for the liquids that the outer bore always points upwardly and optimizes a pressure compensation with the environment. After opening the container for liquids, the resulting relative overpressure in the pressure chamber in relation to the released pressure in the container for liquids effects an opening of the component chamber.