Demonstration of Thenards Blue
aluminum chloride, hexahydrate
cobalt(II)-chloride Xn R 22 S 22-24/25
One can use instead of the chlorides the corresponding oxides/hydroxides. If one uses silicon dioxide instead of aluminum chloride smalt results, boric acid also yields a colorant.
test tube (heat resistant)
burner (preferably gas-)
- One adds in a test tube two spatula-tips of aluminum chloride(hexahydrate) and one spatula-tipful of cobalt(hexahydrate) and mixes them by swaying the tube back and forth.
- Vigorously heat the mixture with the burner. There is soon formed, beginning at seperate points, a strong deep blue coloration, water and hydrochloride acid are vaporized.
- Dispose of the residue as solid heavy metal waste.
One can formulate the formation of Thenards Blue as follows:
2 AlCl3 + CoCl2 + 4 H2O --> CoAl2O4 + 8 HCl
Formation of Thenards Blue
derived from "9. Nachweis als Thenards Blau", p. 425,