634. Determination of Reducing Sugars.—The reducing sugars are estimated as dextrose, and may be determined by any of the methods given for the estimation thereof ([113-140]).

635. Polarization.—All results are to be stated as the polarization of the undiluted sample. The triple field shadow saccharimeter is recommended, and the results are expressed in the terms of the sugar scale of this instrument. If any other instrument be used, or if it be desirable to convert to angular rotation, the following factors may be employed:

1° Schmidt and Haensch= 0°.3468angular rotation D.
1° angular rotation D= 2°.8835Schmidt and Haensch.
1° Schmidt and Haensch= 2°.6048Wild (sugar scale).
1° Wild (sugar scale)= 0°.3840Schmidt and Haensch.
1° Wild (sugar scale)= 0°.1331angular rotation D.
1° angular rotation D= 0°.7511Wild (sugar scale).
1° Laurent (sugar scale)= 0°.2167angular rotation D.
1° angular rotation D= 4°.6154Laurent (sugar scale).

In the above table D represents the angular rotation produced with yellow monochromatic light.

(a) In White Wines or Beers.—Sixty cubic centimeters of wine are decolorized with three cubic centimeters of lead subacetate solution and filtered. Thirty cubic centimeters of the filtrate are treated with one and five-tenths cubic centimeters of a saturated solution of sodium carbonate, filtered and polarized. This gives a solution of nearly ten to eleven, which must be considered in the calculation, and the polariscope reading must accordingly be increased one-tenth.

(b) In Red Wines.—Sixty cubic centimeters of wine are decolorized with six cubic centimeters of lead subacetate solution and filtered. To thirty cubic centimeters of the filtrate, three cubic centimeters of a saturated solution of sodium carbonate are added, filtered and the filtrate polarized. The dilution in this case is nearly five to six, and the polariscope reading must accordingly be increased one-fifth.

(c) In Sweet Wines. (1) Before Inversion.—One hundred cubic centimeters are decolorized with two cubic centimeters of lead subacetate solution and filtered after the addition of eight cubic centimeters of water. One-half cubic centimeter of a saturated solution of sodium carbonate and four and five-tenths cubic centimeters of water are added to fifty-five cubic centimeters of the filtrate, the liquids mixed, filtered and polarized. The polariscope reading is multiplied by 1.2.

(2) After Inversion.—Thirty-three cubic centimeters of the filtrate from the lead subacetate in (1) are placed in a flask with three cubic centimeters of strong hydrochloric acid. After mixing well, the flask is placed in water and heated until a thermometer, placed in the flask with the bulb as near the center of the liquid as possible, marks 68°, consuming about fifteen minutes in the heating. It is then removed, cooled quickly to room temperature, filtered and polarized, the temperature being noted. The polariscope reading is multiplied by 1.2. Because of the action of lead subacetate on invert sugar ([87]) it is advisable to decolorize the samples with other reagents ([87-89]).

(3) After Fermentation.—Fifty cubic centimeters of wine, which have been dealcoholized by evaporation and made up to the original volume with water, are mixed, in a small flask, with well washed beer yeast and kept at 30° until fermentation has ceased, which requires from two to three days. The liquid is washed into a 100 cubic centimeter flask, a few drops of a solution of acid mercuric nitrate and then lead subacetate solution, followed by sodium carbonate, added. The flask is filled to the mark with water, shaken, the solution filtered and polarized and the reading multiplied by two.

636. Application of Analytical Methods.—(1) There is no rotation.—This may be due to the absence of any rotatory body, to the simultaneous presence of the dextrorotatory nonfermentable constituents of commercial dextrose and levorotatory sugar, or to the simultaneous presence of dextrorotatory cane sugar and levorotatory invert sugar.