Part 51

Commercial glucose is used chiefly by confectioners for manufacturing table sirups and for adulterating honey and molasses.

Commercial grape sugar is chiefly employed by brewers as a substitute for barley and other grains.

In Europe, the starch which is converted into glucose, is derived principally from potatoes. The method employed in conversion, whether an acid or diastatic action, is revealed not only by the nature of the product, but also by the composition of its ash. In the case of diastatic conversion the ash of the sample will contain only a trace of sulfates, no chlorin, and be strongly alkaline, while the product of conversion with sulfuric acid will give an ash rich in sulfates with a little lime and be less strongly alkaline.

The process of manufacture in this country consists in treating the starch, beaten to a cream with water, with sulfuric acid, usually under pressure, until the product shows no blue color with iodin. The excess of acid is removed with marble dust, the sirup separated by filtration, whitened by bleaching with sulfurous acid or by passing it through bone-black and evaporated to the proper consistence in a vacuum. The solid sugar, consisting mostly of dextrose, is made in the same manner, save that the heating with the acid is continued until the dextrin and maltose are changed into maltose. The product is either obtained in its ordinary hydrated form or by a special method of crystallization secured as bright anhydrous crystals. Solutions of dextrose, when first made, show birotation, but attain their normal gyrodynatic state on standing for twenty-four hours in the cold, or immediately on boiling.

=254. Methods Of Separation.=—The accurate determination of the quantities of the several optically active bodies formed in commercial glucose is not possible by any of the methods now known. Approximately accurate data may be secured by a large number of processes, and these are based chiefly on the ascertainment of the rotation and reducing power of the mixed sugars, the subsequent removal of the dextrose and maltose by fermentation or oxidation and the final polarization of the residue. The difficulties which attend these processes are alike in all cases. Fermentation may not entirely remove the reducing sugars or may act slightly on the dextrin. In like manner the oxidation of these sugars by metallic salts may not entirely decompose them, may leave an optically active residue, or may affect the optical activity of the residual dextrin. The quantitive methods of separating these sugars by means of phenylhydrazin, lead salts or earthy bases have not been developed into reliable and applicable laboratory processes. At the present time the analyst must be contented with processes confessedly imperfect, but which, with proper precautions, yield data which are nearly correct. The leading methods depending on fermentation and oxidation combined with polarimetric observations will be described in the subjoined paragraphs.

=255. Fermentation Method.=—This process is based on the assumption that, under certain conditions, dextrose and maltose may be removed from a solution and the dextrin be left unchanged. In practice, approximately accurate results are obtained by this method, although the assumed conditions are not strictly realized. In the prosecution of this method the polarimetric reading of the mixed sugars is made, and the maltose and dextrose removed therefrom by fermentation with compressed yeast. The residual dextrins are determined by the polariscope on the assumption that their average gyrodynat is 193. In the calculation of the quantities of dextrose and maltose their gyrodynats are fixed at 53 and 138 respectively. The total quantity of reducing sugar is determined by the usual processes. The relative reducing powers of dextrose and maltose are represented by 100 and 62 respectively. The calculations are made by the following formulas:

R = reducing sugars as dextrose d = dextrose m = maltose dʹ = dextrin P = total polarization (calculated as apparent gyrodynat) Pʹ = rotation after fermentation (calculated as apparent gyrodynat).

Whence R = d + 0.62m (1) P = 53d + 138m + 163dʹ (2) Pʹ = 193dʹ (3)

From these three equations the values of d, m, and dʹ are readily calculated:

Example: To find d and m:

Subtract (3) from (2) P = 53d + 133m + 193dʹ Pʹ = 193dʹ -------------------------------------- P - Pʹ = 53d + 138m (4)

Multiply (1) by 53 and subtract from (4)

P - Pʹ = 53d + 138m 53R = 53d + 32.86m ------------------------------------------- P - Pʹ - 53R = 105.14m (5)

P - Pʹ - 53R Whence m = ------------------ (6) 105.14

d = R - 0.62m (7)

Pʹ dʹ = ---- (8) 193

Sidersky assigns the values [a]{D} = 138.3 and [a]{D} = 194.8 to maltose and dextrin respectively in the above formulas.

Illustration: In the examination of a sample 26.048 grams of midzu ame in 100 cubic centimeters were polarized in a 200 millimeter tube and the following data were obtained:

Polarization of sample in angular degrees 69°.06, which is equal to an apparent gyrodynat of 132.6:

Total reducing sugar as dextrose 33.33 per cent:

Polarization in angular degrees after fermentation 30°.84 = [a]_{D} = 59.2.

Substituting these values in the several equations gives the following numbers:

(1) 0.3333 = d + 0.62m (2) 132.6 = 53d + 138m + 193dʹ (3) 59.2 = 193dʹ (4) 73.4 = 53d + 138m (5) 55.74 = 105.14m (6) m = 0.5301 = 53.01 per cent. (7) d = 3333 - 3286 = 0.0047 = 00.47 per cent. (8) dʹ = 59.2 ÷ 193 = 0.3067 = 30.67 ” ”

Summary: Sample of midzu ame:

Percentage of dextrin 30.67 per cent. ” ” maltose 53.01 ” ” ” ” dextrose 00.47 ” ” ” ” water 14.61 ” ” ” ” ash 00.31 ” ” ----- Sum 99.07 ” ” Undetermined 0.93 ” ”

For polarization the lamplight shadow polariscope employed for sugar may be used, and the degrees of the sugar (ventzke) scale converted into angular degrees by multiplying by 0.3467.

The process of fermentation is conducted as described in the paragraph given further on, relating to the determination of lactose in the presence of sucrose.

=256. The Oxidation Method.=—The removal of the reducing sugars may be accomplished by oxidation instead of fermentation. The process of analysis is in all respects similar to that described in the foregoing paragraph, substituting oxidation for fermentation. For the oxidizing agent mercuric cyanid is preferred, and it is conveniently prepared by dissolving 120 grams of mercuric cyanid and an equal quantity of sodium hydroxid in water mixing the solutions and completing the volume to one liter. If a precipitate be formed in mixing the solutions it should be removed by filtering through asbestos. For the polarization, ten grams of the sugars in 100 cubic centimeters is a convenient quantity. Ten cubic centimeters of this solution are placed in a flask of water marked at fifty cubic centimeters, a sufficient quantity of the mercuric cyanid added to remain in slight excess after the oxidation is finished (from twenty to twenty-five cubic centimeters) and the mixture heated to the boiling point for three minutes. The alkali, after cooling, is neutralized with strong hydrochloric acid and the passing from alkalinity to acidity will be indicated by a discharge of the brown color which is produced by heating with the alkaline mercuric cyanid. The heating with the mercury salt should be conducted in a well ventilated fume chamber.