Another general test for carbohydrates is anthrone reaction. Its
principle is the same as that of Molisch's, except that furfurals and hydroxyl-methyl furfurals offer bluish green condensation products with anthrone.
Anthrone reagent: in conc.H2SO4, 0.2% (w/v) solution.
In a test tube, add about 2 mL of Anthrone reagent to approximately 0.5-1mL of the test solution and mix thoroughly.
Watch if the colour changes to bluish green. If not, after keeping them in a boiling water bath for ten minutes, re-examine the tubes.
A positive test indicates a blue-green color.