Abstract: In the automatic liquid sample diluter disclosed herein, an excess of the sample liquid is drawn into the apparatus through a path which includes a conduit section of precisely predetermined volume. Valving means then switch this conduit section into the diluent discharge path so that accurate dilution ratios are obtained merely by controlling the discharged diluent volume.

Abstract: The diluter disclosed herein consists of a control and drive unit and a diluent module which is connectable to the control and drive unit to form a diluter apparatus. In the diluent module, which can be removed and replaced for the rapid and non-contaminating substitution of diluents, a diluent piston engages the walls of a cylindrical diluent reservoir which has an outlet at one end. A bore through the diluent piston receives and supports a second, smaller piston which can be moved independently of the diluent piston. With appropriate connections to the drive unit, the small piston may be moved in a direction away from the diluent outlet, thereby aspirating a small sample of liquid placed in contact with a spout which communicates with the diluent outlet. Subsequent movement of the diluent piston toward the outlet enables the dispensing from the spout of the relatively small sample of liquid along with a relatively large quantity of diluent.