The mixture is filtered with suction through an asbestos mat supported on a filter paper in a
25-cm. Büchner funnel, and the
barium sulfate is washed with two 100-ml. portions of water. The filtrate and washings are combined, and the clear colorless solution of the sugar is concentrated to about 300 ml. under reduced pressure (
water pump) on a
water bath whose temperature does not exceed 60°. The mixture is filtered, and the solid is washed on the filter with a little water. The combined filtrate and washings are then concentrated to a volume of 100 ml. under the conditions described above. The warm, slightly tan-colored syrup is poured into a
500-ml. Erlenmeyer flask. The transfer is completed by rinsing the distilling flask five times with
40-ml. portions of glacial acetic acid, each portion of the
acetic acid being warmed to 50° in the bath before it is transferred. The
acetic acid solution of the sugar is seeded with crystalline
D-mannose (Note
2), and, after standing overnight at room temperature, the solution is placed in a refrigerator for a day or two.