The present invention is directed to a novel process and apparatus for charging a liquid reactant with a gas. In the process, the liquid reactant which is as yet uncharged with gas is introduced into the gassing tank at a point just below the substantially constant liquid level of the reactant. When the reactant has been charged with gas, it is removed at a point below the region where gassing takes place. A three-layered arrangement is thereby established and maintained in the gassing tank so that the layer of gas is separated from the layer of gas charged component by the layer of uncharged component. The gas charged component is thus maintained at a density corresponding to the desired gas content, taking into account any significant starting conditions, such as the original density, the temperature and the pressure. If necessary, this density is maintained by suitably varying the stirrer speed.