Annatto
Evaporate a portion of the extract to dryness and add sulfuric acid to the residue. If annatto is present a greenish-blue color forms. Should a pink tint result the presence of a coal-tar color is to be suspected.
Coal-Tar Colors
These colors will dye wool or silk if pieces of the fiber are boiled in the diluted alcoholic extract, which has first been acidified with hydrochloric acid. The normal butter coloring matter will not dissolve when thus treated.
Geisler’s Method.—To a few drops of the clarified fat on a porcelain surface, add a very little fullers’ earth. If a pink to violet-red coloration is produced in a short time the presence of an azo-color is indicated.
Saffron
When saffron is present, nitric acid colors the alcoholic extract green, and hydrochloric acid colors it red.
Turmeric
Add ammonia to the alcoholic extract, and if it turns brown it indicates the presence of turmeric.