Abstract: A mixing machine for tumbling a rack which carries a plurality of volumetric glassware tubes containing chemical solutions. The machine includes a stand which rotatively supports a tumbler box adapted to closely receive the rack. The tumbler box includes a floor and a lid which engage the ends of the volumetric tubes to prevent them from shifting in the tumbler box and to hold rubber stoppers in place in the tubes. The tumbler box is rotated by an electric motor having a timing switch and a cam switch that stops the box in an upright position.