sugars than dextrose. Among these, maltose and levulose are sugars with which the student will frequently be brought into contact in the course of his experiments. A freshly prepared solution of maltose containing the α modification has a lower specific rotation than that of the stable "B" modification. On the other hand, the "a" modification of levulose, like that of dextrose, has a higher specific rotation than the “ẞ” or stable modification. It will be evident from these remarks that freshly prepared solutions of both maltose and levulose must be treated in a similar manner to those of dextrose previous to examination in the polarimeter.1 66 The Cupric Oxide Reducing Power of Dextrose, Introducing the Cupric Oxide Reducing Method of Estimating Sugars. Preparation of Fehling's solution. Two solutions are required : (1) Copper Sulphate Solution, prepared by dissolving 69.2 grms. of the pure salt in distilled water and making up the volume of the solution to 1,000 c.c. (2) Alkaline Tartrate Solution, prepared by dissolving 346 grms. of Rochelle salt (sodium potassium tartrate) and 130 grms. of anhydrous sodium hydrate in distilled water and making up the volume of the solution to 1,000 c.c. The solutions must be stored in separate bottles, and when required for use must be mixed in equal volumes. 1 For recent views concerning the mutarotation of dextrose, see H. E. Armstrong, "Studies on Enzyme Action," Journ. Chem. Soc., 1903, lxxxiii., p. 1310. Determination of the Reducing Power of Dextrose.'-Weigh out about 5 grms. of dextrose, dissolve it in 100 c.c. of water, and determine the concentration of the solution from its specific gravity. (See Table I. for divisor.) Prepare the Fehling's solution required by mixing 25 c.c. of the copper sulphate solution with 25 c.c. of the alkaline tartrate solution in a No. 5 spout beaker, and dilute the mixed solution with such a quantity of water that, with the dextrose solution, to be added subsequently, the total volume is 100 c.c. In other words, the Fehling's solution used is diluted with its own volume of liquid. Cover the beaker containing the diluted Fehling's solution with a clock-glass, and heat in a boiling water-bath. After a few minutes, add to the Fehling's solution an accurately measured or weighed volume of the dextrose solution, and continue the heating of the solution for exactly twelve minutes. Filter off the red precipitate of cuprous oxide which is formed through a Soxhlet tube connected with a water pump, and wash it with at least 200 c.c. of boiling water, and afterwards with about 10 c.c. of strong alcohol. Place the Soxhlet tube in a water or hot-air oven and dry at 100° (212° F.). When dry, reduce the cuprous oxide in the tube to metallic copper by gently heating the tube with 1 The standard method proposed by H. Brown, Morris and Millar is adopted. (See Journ. Chem. Soc., 1897, lxxi., p. 278.) a gas flame in a current of dry hydrogen. Allow the tube to cool in a desiccator and weigh. Refer to Table III. to ascertain the amount of dextrose corresponding to the weight of copper found, and compare the weight found with the known weight of dextrose used in the experiment. Calculate the weight of dextrose found as a percentage on the weight of dextrose taken. When judging the proper amount of dextrose to be taken for the reduction experiment just described, some points must be borne in mind: (1) The amount of copper weighed should be not less than 0.15 grm., and not more than 0.35 grm. As dextrose reduces approximately twice its weight of copper, the weight of dextrose taken should be from 0.07 to 0.17 grm. Two c.c. of a 5 per cent. solution would therefore be about the right amount to take. (2) When it is necessary to use less than 2 c.c. of a sugar solution, the experimental error of measurement from a pipette has an appreciable influence on the accuracy of the result. In such case it is advisable to weigh the desired amount of solution accurately, and calculate the volume of the solution used from its weight and specific gravity. (3) As Fehling's solution almost always gives a slight precipitate on heating due to spontaneous reduction, it is necessary to make a blank determination upon every fresh quantity of Fehling's solution prepared, and correct for this in all experi ments in which the solution is used. The amount usually varies from 1 to 3 milligrams of copper. Preparation and Properties of Phenyl-Glucosazone.-Dissolve 1 grm. of dextrose in 50 c.c. of water, and add to the solution 2 grms. of phenylhydrazine dissolved in 2 grms. of 50 per cent. acetic acid. Heat the mixture in a boiling water bath, and observe that the glucosazone slowly separates from the hot solution as a dense yellow precipitate. The action is complete in one hour. Examine the precipitate under the microscope with a 1-inch lens, and note that it is composed of needle-shaped crystals, some of which may occur in fan-shaped aggregates. Make a drawing of the crystals. Filter off the precipitated osazone, wash with hot water, and dry at 100° (212° F.). Note that glucosazone is very insoluble in boiling water; this characteristic assists in its identification. The reaction of phenyl-hydrazine with the hexoses is as follows: If one molecule of phenyl-hydrazine is allowed to act on one molecule of a hexose, a normal hydrazone is formed : Dextrose. Hydrazone. Phenyl-hydrazine. CH2.OH(CH.OH)4.CHO+CH2NHNH2=CH2.OH(CH.OH),.CH+H2O : N-NH.CH, But if two molecules of phenyl-hydrazine are used, an osazone is obtained : CH2.OH(CH.OH)3.C – CH=N N NH.CH. Glucosazone. Cane-Sugar or Saccharose. An experiment has been made (p. 73) on the optical activity of cane-sugar. Solution Density of Cane-Sugar. The solution factors for cane-sugar in solutions of varying concentration are given in Table I. Cane-Sugar does not possess Cupric Oxide Reducing Power.-Dissolve about 1 grm. of pure cane-sugar in a little water, and mix the solution with Fehling's solution under the standard conditions already described (p. 79). Heat the solution for twelve minutes. No reduction takes place. Cane Sugar does not Combine with PhenylHydrazine to Form an Osazone.-Dissolve 1 grm. of cane-sugar in 50 c.c. of water and treat the solution with phenyl- hydrazine as described for dextrose (p. 81). Note that no osazone is formed until after prolonged heating, when a little glucosazone may be formed owing to slight inversion of the cane-sugar by the acetic acid in the solution. Inversion of Cane-Sugar. Cane-sugar is a disaccharide, and when hydrolysed (inverted) by the action of dilute acids or that of the enzyme invertase, is resolved into a mixture of equal parts of dextrose and levulose (invert-sugar), according to the equation: -2 C12H22O11 + OH2 = С ̧H12O6 + С ̧H12O6. Dextrose. Levulose. The change may be demonstrated quantitatively |