The flow sheet for performing residence time distribution measurements is shown in figure . The reactor cartridge R1 is charged within one minute from the top of the replenishing unit Mg with magnesium turnings (23 g for coarse magnesium turnings, 27g for fine magnesium turnings) while the jogging motor M at the bottom of the reactor cartridge is already started. After the reactor cartridge has been filled, the magnesium bed is allowed to settle and be compacted by the vibrations generated by the jogging motor for another 30 minutes. Residence time measurements are performed at room temperature with the jogging motor running at 6 V electrical voltage. The determination of the residence time distribution in the magnesium-filled reactor cartridge is performed using infrared spectroscopy. The IR probe is placed within a PTFE-Tpiece directly at the reactor inlet for measuring the inlet concentrations and directly at the reactor outlet for measuring the outlet concentrations.