Aldehydes are characterized by the reddish-violet colour which they give with a solution of fuchsine that has been decolorized by sulphurous acid (H.
The portion distilling at about 200° C. is then methylated by means of methyl alcohol and methyl iodide at loo-i io C., the excess of methyl alcohol removed and the product obtained decolorized by sulphuric acid.
An aqueous solu tion of fuchsine is decolorized on the addition of sulphurous acid, the easily soluble fuchsine sulphurous acid being formed.
The residue is then dissolved in water, decolorized by animal charcoal and saturated at 50 C. with oxalic acid.
The urea oxalate is recrystallized and decolorized and finally decomposed by calcium carbonate (J.