Verification of aluminium with alizarin
acetic acid 25% C R 10-35 S (1/2)-23-26-45
ethanolic alizarin solution F R 11 S (2)-7-16
- One adds a spatula-tipful of aluminium sulphate into a test tube and dissolves this with approx. 1 ml of acetic acid 25%.
- One adds 4-5 drops of alizarin solution.
- After a while the reaction mixture clarifies and takes on a reddish color.
- The diluted solution can be disposed of in the drainage.
Alizarin forms with aluminium(III) a colored complex. Alizarin (derived from madder root) + alum (potassium aluminum sulfate) was in the past very important for the dyeing of fabrics.
Structural formula of alizarin
Alizarin aluminium complex (left), alizarin solution (right)
Inspired by VII.3, "Aluminiumnachweis als Alizarin-S-Farblack", p. 76, 
see under: Al-Nachweis mit Alizarinsulfonsäure, Natriumsalz