Part 50

The 106.3 milligrams of invert sugar equivalent to c, correspond to 101 milligrams of sucrose. The quantity of dextrose equivalent to 275 milligrams of copper is 142.8. Of this amount 53.15 milligrams are due to the inverted sucrose, leaving 89.65 milligrams arising from the invert sugar and dextrose originally present. This quantity is equivalent to 175 milligrams of copper.

Of the 300 milligrams of copper obtained in the first instance, 125 are due to levulose in the original sample, corresponding to 69.73 milligrams which number, multiplied by two, gives the invert sugar present.

The sample examined, therefore, had the following composition:

Sucrose 101.00 milligrams. Invert sugar 139.46 ” Dextrose 19.92 ” ------ Sum 260.38 ”

On the other hand, if the invert sugar be calculated from the quantity corresponding to the 225 milligrams of copper corresponding to e, the data will be very different from those given above. In this instance of the levulose found corresponding to 225 milligrams of copper, viz., 133.89, 53.15 milligrams are due to the inverted sucrose. Then the quantity due to the invert sugar at first present is 133.89 - 53.15 = 80.74 milligrams. Since half the weight of invert sugar is levulose, the total weight of the invert sugar at first present is 161.48, leaving only 8.91 milligrams due to added dextrose. The difficulties in these calculations doubtless arise from the imperfect destruction of the levulose, and from variations in the reducing action of sugars on copper salts in the presence of such large quantities of sodium chlorid.

=250. Calculation from Data obtained with Copper Carbonate.=—The wide variations observed in different methods of calculations in the preceding paragraph, are due in part to the different degrees of oxidation exerted on alkaline copper tartrate by the dextrose and levulose. Better results are obtained by conducting the analytical work with Ost’s modification of Soldaini’s solution (=128=).

The relative quantities of levulose and dextrose oxidized by this solution are almost identical, and the calculations, therefore, result in nearly the same data, whether made from the numbers obtained with the residual dextrose or from the levulose destroyed. The method of applying this method is illustrated in the following calculation.

Example.—In a mixture of sucrose, invert sugar, and dextrose, the quantities of copper obtained by using the copper carbonate solution were as follows:

Copper obtained before inversion = a = 150 milligrams. ” ” after ” = b = 250 ” ” ” ” destroying lev’e = d = 137.5 ” ” equivalent to inverted sucrose = b - a = c = 100 ” ” ” ” levulose = b - d = e = 112.5 ”

{44.0 milligrams invert sugar. a = 150 milligrams Cu = {45.3 ” dextrose. {42.5 ” levulose. d = 137.5 ” ” = 41.55 ” dextrose. c = 100 ” ” = 29.5 ” invert sugar = 28.025 sucrose. e = 112.5 ” ” = 31.9 ” levulose.

14.75 milligrams of dextrose = 48.5 milligrams Cu. 14.75 ” ” levulose = 51.5 ” ”

137.5 - 48.5 = 89.0 milligrams Cu due to dextrose present before inversion. 89.0 milligrams Cu = 27 milligrams dextrose before inversion. 150.0 - 89.0 ” ” = 61.0 ” Cu due to levulose present before inversion. 61.0 ” ” = 17.8 ” levulose before inversion. 17.8 × 2 = 35.6 milligrams invert sugar present before inversion. 27.0 - 17.8 = 9.2 ” dextrose ” ” ”

Again:

112.5 - 51.5 = 61.0 milligrams Cu due to levulose present before inversion. 61.0 milligrams Cu = 17.8 milligrams levulose. 17.8 ” levulose indicate 35.6 milligrams invert sugar. Dextrose in invert sugar before inversion = 17.8 milligrams. Total dextrose before inversion = 27.0 milligrams. Dextrose above amount required for invert sugar = 27.0 - 17.8 = 9.2 milligrams.

The respective quantities of the three sugars in the solution are, therefore:

Sucrose = 28.025 milligrams. Invert sugar = 35.6 ” Dextrose = 9.2 ”

The calculations made from the later data (=234=) give almost the same results.

=251. Winter’s Process.=—Winter has proposed a method of separating dextrose and levulose in the presence of sucrose based on the selective precipitation produced on treating mixtures of these sugars in solution with ammoniacal lead acetate.

The reagent is prepared immediately before use by adding ammonia to a solution of lead acetate until the opalescence which is at first produced just disappears. The separation is based on the fact that the compound of sucrose with the reagent is easily soluble in water, while the salts formed with levulose and dextrose are insoluble. The separation of the sugars is accomplished as follows:

The ammoniacal lead acetate is added to the solution of the mixed sugars until no further precipitate is produced. The precipitated matters are digested with a large excess of water and finally separated by filtration. The sucrose is found in the filtrate in the form of a soluble lead compound, from which it is liberated by treatment with carbon dioxid. The lead carbonate produced is separated by filtration and the sucrose is estimated in an aliquot part of the filtrate by optical or chemical methods. The precipitate containing the lead compounds of dextrose and levulose is washed free of sucrose, suspended in water and saturated with carbon dioxid. By this treatment the lead compound with dextrose is decomposed and, on filtration, the dextrose will be found in the filtrate, while the lead compound of the levulose is retained upon the filter with the lead carbonate. After well washing the precipitate, it is again suspended in water and saturated with hydrogen sulfid. By this treatment the lead levulosate compound is broken up and the levulose obtained, on subsequent filtration, in the filtrate. The dextrose and levulose, after separation as above described, may be determined in aliquot parts of their respective filtrates by the usual gravimetric methods. Before determining the levulose the solution should be heated until all excess of hydrogen sulfid is expelled.

This method was used especially by Winter in separating the various sugars obtained in the juices of sugar cane. It has not been largely adopted as a laboratory method, and on account of the time and trouble required for its conduct, is not likely to assume any very great practical importance.

=252. Separation of Sugars by Lead Oxid.=—In addition to the combination with the earthy bases, sugar forms well defined compounds with lead oxid. One of these compounds is of such a nature as to have considerable analytical and technical value. Its composition and the method of preparing it have been pointed out by Kassner.

Sucrose, under conditions to be described, forms with the lead oxid a diplumbic saccharate, which separates in spheroidal crystals, and has the composition corresponding to the formula C₁₂H₁₈O₁₁Pb₂ + 5H₂O. The precipitation takes place quantitively and should be conducted as follows:

The substance containing the sucrose, which may be molasses, sirups or concentrated juices, is diluted with enough water to make a sirup which is not too viscous. Lead oxid suspended in water is stirred into the mass in such proportion as to give about two parts of oxid to one of the sugar. The stirring is continued for some time until the oxid is thoroughly distributed throughout the mass and until it becomes thick by the commencement of the formation of the saccharate. As soon as the mass is sufficiently thickened to prevent the remaining lead oxid from settling, the stirring may be discontinued and the mixture is left for twenty-four hours, at the end of which time the sucrose has all crystallized in the form of lead saccharate. The crystals of lead saccharate can be separated by a centrifugal machine or by passing through a filter press, and are thoroughly washed with cold water, in which they are almost insoluble. The washed crystals are beaten up with water into a thick paste and the lead separated as basic carbonate by carbon dioxid. The sucrose is found in solution in the residual liquor and is concentrated and crystallized in the usual way.

Reducing sugars have a stronger affinity for the lead oxid than the sucrose, and this fact is made use of to effect a nearly complete separation when they are mixed together. In order to secure this the lead oxid is added in the first place only in sufficient quantity to combine with the reducing sugars present, the process being essentially that described above. The reducing sugars which are precipitated as lead dextrosates, lead levulosates, etc., are separated in the usual way by a centrifugal or a filter press, and the resulting liquor, which contains still nearly all the sucrose, is subjected to a second precipitation by the addition of lead oxid. The second precipitation obtained is almost pure diplumbic saccharate.

In the precipitation of the sugar which is contained in the beet molasses, where only a trace or very little invert sugar is present, the sucrose is almost quantitively separated, and by the concentration of the residual liquor, potash salts are easily obtained. In this case, after the decomposition of the lead saccharate by carbon dioxid, the residual sugar solution is found entirely free of lead. Where invert sugar is present, however, in any considerable proportions, it is found to exercise a slightly soluble influence on the lead saccharate, and in this case a trace of lead may pass into solution. For technical purposes, this is afterwards separated by hydrosulfuric acid or the introduction of lime sulfid.

Lead oxid is regenerated from the basic lead carbonate obtained by heating in retorts to a little above 260°, and the carbon dioxid evolved can also be used again in the technical process.

=253. Commercial Glucose and Grape Sugar.=—The commercial products obtained by the hydrolysis of starch are known in the trade as glucose or grape sugar. The former term is applied to the thick sirup obtained by concentrating the products of a partial hydrolysis, while the latter is applied to the solid semi-crystalline mass, secured by continuing the hydrolyzing action until the intermediate products are almost completely changed to dextrose. In this country the starch employed is obtained almost exclusively from maize, and the hydrolyzing agent used is sulfuric acid. The products of conversion in glucose are chiefly dextrins and dextrose with some maltose, and in grape sugar almost entirely dextrose. When diastase is substituted for an acid, as the hydrolytic agent, maltose is the chief product, the ferment having no power of producing dextrose. In the glucose of Japan, known as midzu ame dextrin and maltose are the chief constituents.