SEPTEMBER 15,1936
32 1
ANALYTICAL EDITION
carbon simultaneously, in all kinds of steels, by combustion of the steel in oxygen at a high temperature. The results for sulfur are slightly lower than the values commonly accepted as correct, but are consistent and reproducible and satisfactorily accurate for most practical purposes, particularly in high-alloy steels containing little sulfur.
Acknowledgment The authors wish to acknowledge the hela advice. and encouragement of John Johnston a n i to recordtheir appreciation of the cooperation accorded by various members of the United States Steel Corporation Chemists Committee.
Literature Cited (1) Guedras, Aciers spdciaux, 6,76-80(1931). (2) Holthaus, Arch. Eisenhiittenw., 5 9 5 (1931-32).
(3) H o l t h a ~ sStaM , u. Eisen, 44,1514 (1924). (4) Isham and Aumer, J *Am* Chem. SOC., 30,1236-9 (1908). (5) Kar, IND.ENG.CHEM., Anal. Ed., 7,244 (1935). (6) ~ ~Chem.-Ztg,, ~ s7,573-4 ~ (1933). l ~ ~ , (7) Lundell, Hoffman, and Bright, “Chemical Analysis of Iron and Steel,” New York, John Wiley & Sons, 1931. (8) Misson, Chimie & Induatrie, Special No. 27, 326-8 (March, 1932). (9) Rooney, Analyst, 59,278-80 (1934). (10) Schmitz, Stahl u. Eisen, 39,406-12 (1919). (11) Seuthe, Ibid.. 52.445 (1932). (12) Swobodal Chem.9 77,269 (1924). (13) Thanheiser and Dickens, Mitt. Kaiser-Wilhelm Inst. Eisenforsch. DQsseldorf, 15, 255 (1933); Arch. Eisenhattenw., 7, 557-82 (1934). (14) Vita, Stah2 u. Eisen, 40,933 (1920). (15) Zenker, Arch. Eisenhiitfenw., 5,101 (1931-32).
z.
RECEIVED July 23. 1936.
The Dextrose-Levulose Ratio and the Polarizing Constants of Raw Cane Sugars F. W. ZERBAN, New York Sugar Trade Laboratory, Inc., 80 South St., New York, N. Y.
U
NTIL recently the only practical method for the determination of dextrose and levulose in raw sugars was that of Browne ( I ) , based on the difference between sucrose, S, and direct polarization, P, and the total reducing sugars, R. The ratio between S - P and R has been termed the “polarizing constant.” The numerical value of the constant is about 0.3 when the reducing sugars consist of dextrose and levulose in equal proportions, varies inversely with the dextrose-levulose ratio, and becomes negative when this ratio rises above 64 to 36. To calculate the percentages of dextrose and levulose in a raw sugar from S - P and R, Browne makes use of Equations 1 and 2: x + k y = R qy s =P
cz
+
(1)
+
(2)
where x and y are the percentages of dextrose and levulose, respectively, k is the reducing ratio of levulose to dextrose, c the polarizing ratio of dextrose to sucrose at 20” C., c1 that of levulose to sucrose, R the percentage of total reducing sugars, expressed as dextrose, P the direct polarization of the normal weight solution at 20” C., and S the percentage of sucrose found by inversion with invertase. Solving the equations for x and y, CR + S - P y = percentage of levulose =
x
= percentage of dextrose =
- CI - ky
kc
R
The numerical value of c is 52.74 : 66.5 = 0.793, that of el is -92.88 : 66.5 = - 1.397. The latter varies somewhat with concentration and temperature, but in practice only the temperature correction needs to be considered, and it is best to make all polarizations at exactly 20” C. For k an average value of 0.915 may be used if Allihn’s method of reducing sugar determination is employed. Applying this method to the analysis of mixtures of pure sugars, Browne found that it gives very good results when the ratio between sucrose and reducing sugars is low. But when the ratio is high, as in raw sugars, the difference between the sucrose and the direct polarization becomes very small, and any error in the polarimetric readings has a large effect on the percentages of dextrose and levulose found, especially if the errors in the two readings happen to be in the opposite direc-
tion. In one experiment, with a mixture of 98 per cent of sucrose and 1 per cent each of dextrose and levulose, Browne found 0.75 per cent of dextrose and 1.17 per cent of levulosethat is, a percentage ratio of 39.1 between dextrose and total reducing sugars, instead of 50. In 1934 Zerban and Wiley (6)published a new method for the determination of dextrose and levulose in the presence of large amounts of sucrose, extending previous work by Jackson and Mathews (3) to the analysis of raw sugars. The total reducing sugars are determined by the method of Lane and Eynon, and the levulose is determined by selective reduction of a modified Ost’s solution at 55” C. A table of Lane and Eynon factors for 10 ml. of Soxhlet solution and for mixtures of dextrose and levulose in all possible proportions, in the presence of 10 or 25 grams of sucrose, has been given by Zerban and Wiley (4, as well as a method for calculating the percentages of dextrose and of levulose, by successive approximations. The calculation may be shortened materially by the use of Equations 3 and 4: a x + y = R 0.0806 x y = RI
+
(3) (4)
where x and y are the milligrams of dextrose and levulose, respectively, in 100 ml. of solution analyzed. R represents milligrams of total reducing sugars, expressed as levulose, in 100 ml. of solution. It is calculated, as usual, by multiplying the Lane and Eynon factor in Table I by 100, and dividing by the titer found. a is the varying reducing ratio between dextrose and levulose, and is also given in Table I. R1 is the milligrams of apparent levulose in 100 ml. of solution, found by the method of Jackson and Mathews, and corrected for the reducing effect of the sucrose. The factor 0.0806 is the constant reducing ratio of dextrose to levulose in the method of Jackson and Mathews, 12.4 mg. of dextrose having the same reducing effect as 1mg. of levulose. Solution of Equations 3 and 4 gives R -Ri u - 0.0806 y = mg. of levulose in 100 ml. of solution = R - ax z = mg. of dextrose in 100 mi. of solution =
The values of the denominator, cluded in Table I.
Q
- 0.0806, are also in-
INDUSTRIAL AND ENGINEERING CHEMISTRY
322
TABLE I. LANEAND EYNONFACTORS AND REDUCINQRATIOS DETERMINATIOX OF DEXTROSE AND LEVULOSE IN RAW SUQARS
FOR
Grams of SucroseGrams of Sucres- -25 Lane Lane ReReand and ducing ducing Eynon Eynon ratio, a aratio, Titer factor a a 0.0806 0.0806 Titer factor
7-10
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
48.1 48.0 47.9 47.9 47.8 47.7 47.6 47.5 47.5 47.4 47.3 47.2 47.1 47.1 47.0 46.9 46.8 46.8 46.7 46.7 46.6 46.6 46.5 46.5 46.4 46.4 46.4 46.3 46.3 46.2 46.2 46.2 46.2 46.1 46.1 46.1
1.0434 1.0430 1.0426 1.0422 1,0418 1,0414 1.0410 1.0406 1.0402 1.0398 1.0394 1.0390 1.0386 1.0382 1.0378 1.0374 1.0370 1.0366 1.0362 1.0358 1.0354 1.0350 1.0346 1.0342 1.0338 1.0334 1.0330 1.0326 1.0322 1.0318 1.0314 1.0313 1.0312 1.0312 1.0311 1.0311
0.9628 0.9624 0.9620 0.9616 0.9612 0.9608 0.9604 0.9600 0.9596 0.9692 0.9588 0.9584 0,9580 0.9576 0,9572 0.9568 0.9564 0.9560 0,9556 0,9552 0.9548 0.9644 0.9540 0.9536 0,9532 0.9628 0.9524 0,9520 0.9516 0,9512 0.9508 0.9507 0.9506 0.9506 0,9505 0,9505
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
37
38 39 40 41 42 43 44 45 46 47 48 49 50
44.7 44.6 44.4 44.3 44.1 44.0 43.9 43.8 43.7 43.6 43.5 43.4 43.3 43.2 43.1 43.0 42.9 42.9 42.8 42.7 42.6 42.6 42.5 42.5 42.4 42.3 42.2 42.1 42.1 42.0 41.9 41.8 41.7 41.7 41.6 41.5
1.0419 1.0396 1.0375 1.0356 1.0339 1.0324 1.0311 1.0300 1,0290 1.0281 1.0273 1.0266 1.0260 1,0255 1.0261 1.0248 1.0247 1.0247 1.0246 1.0246 1.0246 1.0245 1.0245 1.0245 1.0245 1.0245 1.0244 1.0244 1.0244 1,0244 1.0244 1.0243 1.0243 1,0243 1.0243 1.0243
0.9613 0.9590 0.9569 0.9550 0.9633 0.9518 0.9505 0.9494 0.9484 0.9475 0.9467 0.9460 0.9454 0.9449 0.9445 0.9442 0.9441 0.9441 0.9440 0,9440 0.9440 0.9439 0.9439 0.9439 0.9439 0.9439 0.9438 0.9438 0.9438 0.9438 0.9438 0.9437 0 * 9437 0.9437 0.9437 0.9437
There is a small error in the final result for dextrose and levulose, because the reducing ratio between the two sugars varies not only with the concentration of either present alone, but slightly also with the proportion between the two, but this error does not exceed 0.23 per cent of the final results. In the analysis of mixtures containing 0.5 to 1.5 per cent of total dextrose and levulose, the remainder being sucrose, the maximum experimental error was found to cause a change of only 2 units in the percentage ratio between dextrose and total reducing sugars, considerably Iess than in the older method based on combined polarimetric and reduction measurements. The mean error was only * L O unit. However, when mixtures with a high proportion of reducing sugars and only small quantities of sucrose are to be analyzed, the older method wilI give more reliable results because the error in the reducing sugar determinations becomes greatly multiplied. When either of the two methods described is applied to the analysis of raw sugars, other sources of error arise, due to the presence of nonsugars which may be optically active or have copper-reducing power, and possibly of other reducing sugars besides dextrose and levulose. Optically active impurities will alter the direct polarization, although they do not affect the sucrose value, provided that invertase is used for hydrolysis. The impurities are a t least partially removed by proper clarification. The polarization after deleading must be used for P, and not the direct polarization in the presence of excess lead. It is necessary, therefore, to delead the entire filtrate from the lead precipitate, and to determine P and S in the r e sulting solution. Under these circumstances the volume of the lead precipitate does not affect the difference between S and P.
not been able to find such nonsugars in cane products, and even advise against the use of lead acetate because it may precipitate reducing sugars. There is general agreement, however, that it is necessary to remove calcium salts and also any excess of lead if used. The safest way probably is to clarify with a minimum of neutral lead acetate, and to remove the excess lead. This procedure has been used in the present investigation, dry potassium oxalate being added to the filtrate from the lead precipitate to remove both lead and calcium. Because of our meager knowledge of the errors caused by the impurities still remaining after clarification, it is impossible to tell definitely which of the two methods may be expected to give more reliable results in the analysis of actual sugar products. This will depend in a large measure on the purity of the material to be analyzed. The results obtained with mixtures of pure sugars would indicate that the method combining polarization and reducing power is preferable for low-purity products that are high in reducing sugars. I n the case of high-purity products with low content of reducing sugars, the amount of reducing nonsugars is probably small in comparison to the total reducing sugars. Furthermore, if two copper-reduction methods are combined, the effect of the presence of other reducing substances besides dextrose and levulose may be expected to be similar in both.
Application of Methods The errors in polarimetric measurements may be greatly reduced by the use of modern high-precision equipment, and in individual cases the choice between methods will be determined by the apparatus available. The limitations of all combined methods must always be kept in mind in the interpretation of results. Both methods described above have been applied to the analysis of 100 typical raw sugars received by the New York Sugar Trade Laboratory during the past 2 years. These included 33 samples from Cuba, 21 from Puerto Rico, 15 from the Philippines, 10 from Hawaii, 9 from Santo Domingo, and 12 from miscellaneous sources. It is usually not known how much time has elapsed between the manufacture of a given sugar and its discharge a t mainland ports. For this reason the results obtained reflect merely the composition of the sugar after arrival at its destination, and not in its original state. There were two samples, however, which were known to have been stored for a t least one year, and the results obtained with these are discussed separately (Table VI). I n order to save space, the results are not given in full, but some typical examples are shown in Table 11. The method combining polarization and reducing power is designated as I, and that based on two different copper-reduction methods as 11. The polariscopic work was done by C. A. Gamble; the reducing sugar determinations in the first half of the samples were made by M. H. Wiley, in the second half by Carl Erb.
INDIVIDUAL SAMPLES TABLE 11. ANALYSESOF SOME -I
-Method
No. 66 67 83 91 16 24 32 43 6 37 54 47
Clarscation There is considerable difference of opinion with regard to clarification prior to reducing-sugar determinations. Some writers maintain that treatment with neutral lead acetate is necessary in order to remove reducing nonsugars; others have
VOL. 8, NO. 5
R' 1.55 1.40 0.73 0.73 0.88 1.06 1.23 1.16 0.61 1.03 1.12 0.94
D % ' Rb'' 55.5 41.9 47.5 45.1 51.5 48.8 51.5 49.6 45.0 66.2 46.2 65.7
-Method RcP)'
0.181 0.480 0.358 0.412 0.273 0.330 0.268 0.311 0.413 0.166 0.386 -0.043
11-
Ra
0 % Rb
1.55 1.39 0.73 0.73 0.88 1.06 1.23 1.15 0.60 1.03 1.10 0.94
55.7 47.1 44.6 41.8 51.0 52.3 47.0 44.9 49.8 54.8 56.4 '59.1
(8 & P ) /
0.175 0.386 0.425 0.478 0.273 0.265 0.366 0.348 0.315 0.195 0.155 0.106
Per cent of total reducing sugars found.
b Percentage ratio of dextrose to total reducing sugars.
Polarizing constant: in method I1 calculated from dextrose and levulose found. C
SEPTEMBER 15, 1936
ANALYTICAL EDITION
323
what narrower range than method I. For both Santo Dominican and Philippine sugars method I gives a higher average polarizing constant than method 11. It is interesting to note in this connection that many years ago Browne (2), using the IN PERCENTAGE RATIOS OF DEXTROSE Herzf‘eld method of sucrose determination, also found low TABLE111. DIFFERENCES AND TOTAL REDUCING SUQARS, FOUND BY THE Two METHODS polarizing constants, around 0.2, for the Philippine mat sugars Difference in Ratio Cases of that time, while Cuban sugars gave constants of about 0.35.
The differences between the results obtained by the two methods, in terms of the ratio of dextrose to total reducing sugars, are summarized in Table 111,for all 98 cases.
Within Within Within Within Within Within Within Within Within Within Within Within Within Within Within Within
1 unit 2 unjts 3 units 4 units 5 units 6 units 7 units 8 units 9 units 10 units 11 units 12 units 14 units 16 units 18 units 19 units
11 25 32 38 48 64 69 76 81 86 92 94 95 96 97 98
In many cases the ratio of dextrose to total reducing sugars found by method I agrees closely with that obtained by method 11, but in others there are considerable divergences, amounting in four cases to more than 12 units, with a maximum of 18.4. Corresponding differences are found in the polarizing constants. The total range of the percentage ratio of dextrose to total reducing sugars was found to be from 32.6 to 67.4 for method I, and from 35.3 to 65.6 for method 11. The range of the polarizing constant was from -0.079 to 0.683, and from -0.040 to 0.628, respectively. However, the average ratios were practically the same (50.4 by method I, 50.7 by method 11), and likewise the polarizing constants (0.293 by method I, 0.285 by method 11), indicating that the errors in the two methods are merely due to experimental difficulties, and not of a systematic nature. The discrepancies between the two methods in individual cases may be caused partly by the fact that in method I the determinations are made on separate portions of a sample, one clarified with lead subacetate and the other with neutral lead acetate, while in method I1 only one solution is prepared, clarified with neutral acetate, and both determinations are made on aliquots of the same filtrate. The average dextrose ratio for all the sugars is practically that of invert sugar. The extent of the deviations from the 50:50 ratio between dextrose and levulose is summarized in Table IV for both methods. OF DEVIATIONS TABLEIV. EXTENT
Ratio Between 49 and 51 Between 48 and 52 Between 47 and 53 Between 46 and 54 Between 45 and 55 Between 44 and 56 Between 43 and 57 Between 42 and 58 Between 41 and 59 Between 40 and 60 Between 32 and 68
Number of Cases Method I Method I1 8 24 22 31 28 46 40 58 52 63 60 73 66 84 75 85 83 89 86 92 98 98
Taking method I1 as the basis, the ratio of dextrose to total reducing sugars is within 40 to 60 per cent in all but six cases, and between 45 and 55 per cent in nearly two-thirds of all samples. Even in extreme cases the amount of levulose is only about twice that of the dextrose, or vice versa. According to method I, the deviations from the 50 per cent ratio are somewhat larger. The average dextrose-ratio and polarizing constants for each of the geographical districts represented by nine or more samples are shown in Table V. Table V shows that even for single geographical districts the average ratio between dextrose and levulose does not deviate much from that for invert sugar. The average polarizing constants vary from about 0.02 to 0.4, method I1 giving a some-
TABLEV. AVERAQEDEXTROSE-RATIO AXD POLARIZING CoxSTANTS
-Method
D/R
I--
-Method
- P)/R
(S
D/R
%
% Cuba Piierto Rico Srtnto Doming0 Hawaii Philippines
49.7 53.7 45.8 48.9 49.3
11--
(S - P)/R
0.305 0.221 0.394 0.326 0.317
47.8 51.9 49.7 48.0 53.5
0.348 0.256 0.307 0.349 0,224
The remaining two samples, referred to previously, were known to have been produced in Cuba in the crop year of 1934, on the same plantations from which came two other samples, manufactured in 1935. The analyses made in 1935, of the two pairs of sugars, gave the results shown in Table VI. TABLEVI. ANALYSESOF Two PAIRS OF SUQARS N 3. 70 newcrop 69: old crop 72, new crop 71. old crop
-MethodIR D % R (S P ) / R 0.531 0.471 42.4 1.245 63.1 0.016 0.431 42.7 0.464 0.991 59.6 0.091
-
C-
R 0.531 1.240 0.430 0.985
Method 1D % R (S - P ) / R 45.6 0.395 76.5 -0.274 50.2 0.302 74.5 -0.234
In both cases the amount of total reducing sugars in the old crop samples is more than twice that in those from the new crop, and at the same time the dextrose ratio is very much higher. Although the sugars were produced in different years, there is a strong indication that the old-crop sugars have undergone inversion during storage, and that levulose has been destroyed through the activity of Torulas. Such cases have also been observed by Browne (9). The two methods described will next be applied to the analysis of molasses.
Literature Cited (1) (2) (3) (4)
Browne, J . Am. Chem. SOC.,28, 439 (1906). Browne, Louisiana Planter, 61, 202 (1918). Jrmkson and Mathewvs, Bur. Standards J. Research, 8, 493 (1932). Zerban and Wiley, IND.ENG.CHEM., Anal. Ed., 6, 354 (1934).
RECEIVED April 27, 1936. Presented before the Division of Sugar Chemistry at the 91st Meeting of the American Chemical Society, Kansas City, M o . , April 13 to 17, 1936.
CORRECTION. In the article on “The Determination of Silica in Boiler Water” [IND. ENQ.CHEM.,Anal. Ed., 6, 364-7 (1934)] which has been incorporated in the 8th edition of “Standard Methods for the Examination of Water and Sewage,” the figure 1.54 given for the dilution factor on page 366 is an experimental one and in the 8th edition has been corrected to the calculated figure 1.56. This figure is independent of any other dilution factor which may enter into the standardization of the color standards used. M. C. SCHWARTZ
-
COERECTION.In the article on “Quantitative Determination of thtr Concentration of Vaporized Carbon Tetrachloride,” by Olsen, Smyth, Ferguson, and Scheflan [IND. ENQ.CHEM.,Anal. Ed., a,, 261 (1936)], the first sentence under the heading “Set IV”
in the second column should read: “The tests outlined in set I1 were repeated using the improved method described in set 111.”
