In the manipulation twenty-five cubic centimeters each of the copper and alkali solutions are mixed and boiled and an equal volume of the maltose solution added, which should not contain more than one per cent of the sugar. The boiling is continued for four minutes, an equal volume of cold recently boiled water added, the cuprous oxid separated by filtration and the metallic copper obtained in the manner already described. The weight of maltose oxidized is then ascertained from the table.
- Example. Weight of impure maltose taken, ten grams to a liter:
- Quantity used, twenty-five cubic centimeters:
- Weight of copper obtained 268 milligrams:
- Weight of maltose oxidized 237 milligrams:
- Weight of impure maltose taken 250 milligrams:
- Percentage of maltose in sample 94.8.
Table for Maltose.
- (A) = Milligrams of copper.
- (B) = Milligrams of maltose.
145. Preparation of Levulose.—It is not often that levulose, unmixed with other reducing sugars, is brought to the attention of the analyst. It probably does not exist in the unmixed state in any agricultural product. The easiest method of preparing it is by the hydrolysis of inulin. A nearly pure levulose has also lately been placed on the market under the name of diabetin. It is prepared from invert sugar.
Inulin is prepared from dahlia bulbs by boiling the pulp with water and a trace of calcium carbonate. The extract is concentrated to a sirup and subjected to a freezing temperature to promote the crystallization of the inulin. The separated product is subjected to the above operations several times until it is pure and colorless. It is then washed with alcohol and ether and is reduced to a fine powder. Before the repeated treatment with water it is advisable to clarify the solution with lead subacetate. The lead is afterwards removed by hydrogen sulfid and the resultant acetic acid neutralized with calcium carbonate.
By the action of hot dilute acids inulin is rapidly converted into levulose.
Levulose may also be prepared from invert sugar, but in this case it is difficult to free it from traces of dextrose. The most successful method consists in forming a lime compound with the invert sugar and separating the lime levulosate and dextrosate by their difference in solubility. The levulose salt is much less soluble than the corresponding compound of dextrose. In the manufacture of levulose from beet molasses, the latter is dissolved in six times its weight of water and inverted with a quantity of hydrochloric acid, proportioned to the quantity of ash present in the sample. After inversion the mixture is cooled to zero and the levulose precipitated by adding fine-ground lime. The dextrose and coloring matters in these conditions are not thrown down. The precipitated lime levulosate is separated by filtration and washed with ice-cold water. The lime salt is afterwards beaten to a cream with water and decomposed by carbon dioxid. The levulose, after filtration, is concentrated to the crystallizing point.[110]
146. Estimation of Levulose.—Levulose, when free of any admixture with other reducing sugars, may be determined by the copper method with the use of the subjoined table, prepared by Lehmann.[111] The copper solution is the same as that used for invert sugar, viz., 69.278 grams of pure copper sulfate in one liter. The alkali solution is prepared by dissolving 346 grams of rochelle salt and 250 grams of sodium hydroxid in water and completing the volume to one liter.