Bial's Test for Pentoses

Bial's reagent uses orcinol, HCl, and FeCl3. Orcinol forms colored condensation products with furfural generated by the dehydration of pentoses and pentosans. It is necessary to use DILUTE sugar solutions with this test (0.02 M).

Method

Add 2 ml of the solution to be tested to 5 ml of Bial's reagent. Gently heat the tube to boiling. Allow the tube to cool. Formation of a green colored solution or precipitate denotes a positive reaction.