Microscale chemistry with a coin and a can
Mahmoud K. El-Marsafy, Peter Schwarz

6. Galvanic Cells with a Pfennig, a tin and the closure of a Cola can

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Photos 6.1 - 6.3
Potentials between Cola can closure, Cola can tin and Pfennig on the skin
1: Closure (Al) // surface of skin // tin (Fe)  2:   tin (Fe)   // surface of skin // Pfennig (Cu)
3: closure (Al) // surface of skin // Pfennig (Cu)

The skin acts as electrolyte in three Galvanic Cells. The multimeter shows the potentials between the three combinations: In the Al/Cu cell the potential is about the sum of the potentials in the two other cells.
As soon as the multimeter is switched to current  direct currents between 0.5 and 5 microamperes are flowing from the more noble to the less noble metal.
Electron transfer from the negative electrodes (anode) to the positive electrodes (interface metal // electrolyte)
takes place while a current is observed.

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