A type of column used for liquid–liquid extraction that has fitted agitators, horizontal rings with a central opening, and vertical baffles attached (p. 264) to the inside of the column wall. The rings divide the column into a series of mixing zones and the vertical baffles enhance mixing. In the centre of each mixing zone is a flat-bladed Rushton turbine. All the turbines are mounted on a common shaft along the axis of the column. The light phase is fed into the bottom of the column and the heavy phase into the top. These are respectively removed from the top and bottom of the column once extraction is complete.