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Me11 Combine two Cola cells to make one Cola battery

In a previous experiment you have learned the voltage of a Galvanic Cell can be doubled by connecting it in series with a second one. Now you will compare the voltages between aluminium and iron in one cell and in batteries of two and three cells.
What you need
3 closures (Al) and  3 metal strips from a Cola can (recycling button Fe), 2 insulated wires with 4 crocodile clips, digital Multimeter, empty container of a mucic cassette as a stand for 6 vials (3 ml), 2 more crocodile clips to connect two of the Al electrodes with Fe electrodes, 3 read wool threads (30 mm) as salt bridges, salt water.
Experiment
* Place 2, 4, 6 vials (3-ml) with salt water into the stand. * Connect vial 1-2, 3-4, 5-6 by three salt bridges.
* Cut Fe electrodes fitting into the vials, clean their upper and lower ends by sand paper. * Cut three closures.
* Left: Connect one Al electrode and one Fe electrode with the multimeter. * Dip them into vials 1 and 2.
* Middle: Remove the Fe-electrode from vial 2, dip it into vial 4.
* Dip the first Fe- and Al electrodes (connected by a crocodile clip) into vials 3 and 4.
* Right: Remove the Fe-electrode from vial 4, dip it into vial 6.
* Dip the remaining Fe- and Al electrodes (connected by a crocodile clip) into vials 4 and 5.
Observation: The meter with one cell reads a negative voltage because the electrodes were connected to the wrong wires.
* The voltage of the single cell is doubled by connecting it with a second one and trippled by connecting it with a third one.
Explanation: In batteries (= Galvanic Cells in series) the voltages of the cells add up.