Abstract: A preheater in the form of a vertical column for treating a vitrifiable composition introduced into the column at the top and which moves through the column by the force of gravity. The vitrifiable composition, which ultimately moves from the column to feed a glass-smelting furnace is treated through heat exchange with hot gases from a regenerator or recuperator of the smelting furnace which move upwardly through the column, against the flow of the vitrifiable composition. An element is located within the column to form a mixing chamber for hot gases within the region of the element and an upper sloping alignment of the vitrifiable composition which takes shape below the element, as well as to provide means for decelerating movement of the vitrifiable composition within the region of the axis of the column so that movement of the vitrifiable composition throughout the cross section of the column is substantially uniform.