Abstract: A pulsed-flow apparatus for spectrometers and the like has a mixing chamber and two syringes each adapted to contain a different liquid and both connected to the mixing chamber. The plunger of each syringe has an outwardly extending rod provided with a toothed rack. A pair of electric armatures are provided, each reciprocable lengthwise of one of the rods and carrying a pressure spring which moves with the armature and, during each move of the armature towards the syringe, advances the plunger deeper into the syringe by the length of one tooth of the rack, but does not extract it when the armature subsequently moves in the opposite direction.