Bial's test is a chemical test for the presence of pentoses. The components include orcinol, hydrochloric acid, and ferric chloride. In the presence of a pentose, the pentose will be dehydrated to form furfural. The solution will turn bluish and a precipitate may form. The solution shows two absorption bands, one in the red between B and C and the other near the D line [1].
Bial's reagent consists of 0.4gm orcin, 200 ml of concentrated hydrochloric acid and 0.5 ml of a 10% solution of ferric chloride [2].