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Materials
Fig. 1 - 2: Tray, re-usable tablet container with 8 blisters, battery water (1), fresh water (2), soda water (3), water with table salt (4), water with Dead Sea salt (5), water with Kaiser Natron (6), water with washing soda (7), lime water (8), 9-Volt battery, two insulated copper wires with crocodile clips, light emitting diode (LED), pencil lead, spatula (cut from a drinking straw) , plastic pipette, stirring rod (piece of insulated copper wire), tissue paper.

Experiment
1. Add spatula tips of table salt, Dead Sea Salt, Kaiser Natron and washing soda to blisters 4, 5, 6 and 7.
2. Starting with battery water add 10 drops to blister 1, 4, 5, 6 and 7.
3. Put 10 drops of fresh water into blister 2, 10 drops of soda water into blister 3 and 10 drops of lime water into blister 8.
4. Stir in blisters 4 - 7 to dissolve the salts. Clean the stirring wire after each use.
5. Connect the positive terminal of the battery with the pencil lead and the negative terminal with the short wire of the LED.
6. Starting with blister 1, close the circuit by dipping the free ends (wire and lead) into the liquid.
7. Go on with blisters 2, 3, 8, 4, 5, 6, 7. 
Observations
1. The LED show light of different brightness in blisters 2 - 8. See Fig. 3 showing blister 4.
2.  In blister 1 no light at all can be seen.
Explanation
1. Die Leitung des Stroms durch Flüssigkeit besorgen positiv und negativ geladenene Teilchen (Ionen).
    Je mehr davon gelöst sind, desto mehr Strom fließt, und desto heller leuchtet die LED
2. Auch in Blister 1 sind Ionen vorhanden. Der von ihnen ermöglichte Stromfluss lässt sich nicht durch die LED testen, wohl aber durch ein hochohmiges Messgerät registrieren.
Addition  See experiment 3.3
To prevent chemical reactions during measuring electric conductivity alternative current is needed.