Ions are responsible for electric conductivity of aqueous solutions. The name ion it is derived frome the Greek language word for "migration".
Using ions of coloured substances you can visualize the migration of ions: Positive and negative ions migrate in an electric field attracted by the negative and the positive electrode respectively.
Many dyes are salts. The colour of the food dye cochenille red A is generated by its negative ions (anions), the colour of methylene blue by its positive ions (cations).

4.6 Ions on the hike
Material
Photo 1: tray, 6 batteries (9 Volt), 2 wires with crocodile clips, 1 clean miscroscope slide, 1 pencil lead (d 2 mm), 2 paper clips covered with plastic, thread, filter paper, sticky tape, tweezers, scissors, dropper bottles (10 ml) with solutions of sodium sulfate and methylen blue, food dye cochenille read A (E 124).
Experiment (Photo 2)
1. Cut a stripe of filter paper as broad as of the slide and 2 cm longer.
2. Fold the stripe around the slide. Fix it on the lower side.
3. Prepare two pencil leads that are 1 cm longer than the slide´s breadth.
4. Fix them at the sides with paper clips - like seen in photo 2.
. . These electrodes must have a free end to fix the corocodile clips. .........................Material................................Setup for ion migration 1. . . . . . . 5. Completely wet the paper and the electrodes with sodium sulfate solution.

6. Connect the 6 batteries in series - like seen in Photo 2 -. Press 10 of the 12 terminals together like popers.
7. Connect the black wire with the negative terminal and the red one with the positive terminal.
8. Soak cochenille read into the thread. Place it on the middle of the wetted paper parallel to the electrodes.
9. Repeat 1 - 9 with methylene blue.
Observations and Explanations