Abstract: A metal treatment vessel having an inlet for the successive introduction of reactive additive and molten metal to be treated, a reaction chamber downstream of the flow of molten metal for successive receipt of the additive and the molten metal and an outlet downstream of the flow of metal in the reaction chamber; the inlet being provided with means for directing the additive and molten metal into the reaction chamber, the dimensions of the inlet to the reaction chamber and the outlet therefrom being such that in operation the molten metal rises in an overhead space provided in the reaction chamber to cover the additive and to seal off the inlet.Retaining means may be provided within the reaction chamber to retain the additive against the flow of molten metal. The inlet at the point of entry into the chamber is preferably at an angle to the vertical whereby the additive and molten metal are deflected into the reaction chamber.