=169. Levulose.=—The levulose group of sugars, wherever it occurs, when oxidized with nitric acid, gives rise to tartaric, racemic, glycolic and oxalic acids, which are not characteristic, being produced also by the oxidation of other carbohydrates. A more distinguishing test is afforded by the color reactions produced with resorcin.[135] The reagent is prepared by dissolving half a gram of resorcin in thirty cubic centimeters each of water and strong hydrochloric acid. To the sugar solution under examination an equal volume of strong hydrochloric acid is added, and then a few drops of the reagent. The mixture is gently warmed, and in the presence of levulose develops a fire-red color. Dextrose, lactose, mannose and the pentoses do not give the coloration, but it is produced by sorbose in a striking degree, and also by sucrose and raffinose since these sugars contain the levulose group. =170. Galactose.=—The galactose which arises from the hydrolysis of milk sugar is readily recognized by the mucic acid which it gives on oxidation with nitric acid.[136] The analytical work is conducted as follows: The body containing galactose or galactan is placed in a beaker with about sixty cubic centimeters of nitric acid of 1.15 specific gravity for each five grams of the sample used. The beaker is placed on a steam-bath and heated, with frequent stirring, until two-thirds of the nitric acid have been evaporated. The residual mixture is allowed to stand over night and the following morning is treated with ten cubic centimeters of water, allowed to stand for twenty-four hours, filtered through a gooch, and the collected matter washed with twenty-five cubic centimeters of water, dried at 100° and weighed. The mucic acid collected in this way will amount to about thirty-seven per cent of the milk sugar or seventy-five per cent of the galactose oxidized. Raffinose yields under similar treatment, about twenty-three per cent of mucic acid, which proves that the galactose group is contained in that sugar. Raffinose, therefore, is composed of one molecule each of dextrose, levulose, and galactose.