January, 1925
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
51
_.
Inversion Losses in Cane Sugar Manufacture’ By C . F. Walton, Jr., M. A. McCalip, a n d W. F. Hornberger CARBOHYDRATE
LABORATORY, BUREAUOF
CHEMISTRY, WASHINGTON,
D. C.
8-When water is evapoR E V I E W of the Loss of sucrose d u e to inversion has been carefully inrated, as in ordinary factory literature on the hyvestigated in a n u m b e r of i n d u s t r i a l procedures f o r c a n e practice, the actual amount drolysis of the polys u g a r m a n u f a c t u r e . Analytical m e t h o d s of a s u i t a b l e of acid in unit volume (concentration of titrated acid) is saccharides reveals a very degree of precision have been selected, a n d t h e typical not only increased, if the acid large number of papers on operations of heating a n d defecating t h e juice, concenis nonvolatile, but the activthis i m p o r t a n t s u b j e c t . t r a t i n g t h e juice in multiple-effect evaporators a n d v a c u u m ity of the hydrogen ion is For an excellent review of pan, a n d finally crystallizing, have been reproduced on a also increased as a result of work done from 1818 to small scale, in so far as t h e controlling factors of t i m e , the removal of water and c o r r e s p o n d i n g increase in t e m p e r a t u r e , pH, a n d sucrose concentrations are con1906, the reader is referred sucrose concentration. to a report by Caldwell,2 cerned. T h e variation in pH of juice d u r i n g t h e sequence which contains a bibliogof t r e a t m e n t from defecation t o crystallization has been Purpose of t h i s Investiraphy of about one hunstudied. T h e d a t a indicate that in befecating c a n e juice gation d r e d a n d f o r t y papers. for r a w s u g a r m a n u f a c t u r e t h e initial pH at which it is T h e r e s e a r c h e s upon From 1906 to date, many safe to carry t h e juice lies between 7.0 a n d 8.0-i. e., at s u c h which the most recent oonimportant c o n t r i b u t i o n s a p o i n t that t h e r e s u l t i n g s i r u p has a p H value between ception of inversion is based h a v e b e e n made to the 6.7 a n d 7.0. In t h e sulfitation process, by which direct have been made on pure suknowledge of t,he subject, c o n s u m p t i o n s u g a r is produced, a lower p H a n d correcrose solutions under carea short b i b l i o g r a p h y of spondingly higher t i t r a t e d acidity m a y be safely carried. fully controlled conditions. which has been prepared by T h e sulfites present in t h e s e sugarhouse liquors apparently The problems become more the authors. r e t a r d t h e progressive increase in acidity by t h e decompocomplicated when an atT o summarize briefly the sition of dextrose a n d fructose, a n d m a y - a l s o possess a tempt is made to apply the results of researches on the specific i n h i b i t i n g property as regards inversion of sucrose. findings of pure chemistry hydrolysis (commonly to the varying conditiorts of termed inversion) of sucrose. it suffices to point out that by far the greater number of the in- actual factory practice. For several reasons itlhas been cliffivestigations so far reported have been concerned with a purely cult to investigate inversion carefully in the factory. One theoretical study of the mechanism and kinetics of the reac- is the well-recognized difficulty of taking corresponding samtion. It may be of interest to state briefly what the present- ples throughout the sugarhouse. Moreover, most sugarhouses day theory includes. The experimental data appear to do not have laboratories sufficiently well equipped for the substantiate the following conception of inversion as of direct careful work which is necessary in studying such a problem. application to sugar manufacture : As a result of these difficulties, little reliance has been placed 1-Jf the weight of sucrose and the volume of the solution are in the past on such analytical data as have been reported on kept constant, the more acid there is present the more rapidly the sugarhouse chemical control sheets which might or might not inversion proceeds. be considered indicative of inversion. It has rather been the 2-All other conditions being constant, a strongly dissociated custom to compare the results of actual practice with those acid, such as hydrochloric or sulfuric, inverts sucrose more rapidly than does a weak acid, such as acetic. For this reason recorded over a number of years from various factories oontitrated acidities, although useful in controlling factory operations, sidered representative of the best performance. I n other are not the real measure of the tendency of juice or sirup to un- words, the tendency has been to accept figures for the actual dergo inversion. recovery of sucrose and the quantity of molasses produced per 3-The velocity of inversion increases with rise in temperature. 4-The rate of inversion, when the time, temperature, and ton of cane, or from juice of stated purity, as the best index of volume concentration of acid are constant, increases with increas- factory performance that has been available under all ciring sucrose concentration. This acceleration in rate does not cumstances. Admittedly, these criteria for estimating instrictly follow the law of mass action as sometimes applied todilute version in actual practice are of great value, and they will solutions, without regard to the mass of water, but is also dedoubtless always be given proper weight. pendent on the amount of water (both free and combined) present I n reviewing that portion of the literature which pertains in the system and the “activity of the hydrogen ion” or “thermodynamic concentration of hydrogen ion.” directly to experimental study of the inversion of sucrose in Note-Recent investigations have established the fact that pH values, juice, sirup, and other sugarhouse products, it has been as customarily determined, involve the “activity of the hydrogen ion” found that, for the most part, procedures have been used in (also termed “thermodynamic concentration of hydrogen ion”) and are not the laboratory which are subject to criticism because tbey solely correlative with the hydrogen-ion concentration (commonly interhave not accurately reproduced factory operating conditions. preted by the dissociation theory as number of hydrogen ions in unit volume). 5-Por a given volume concentration of acid in sucrose solu- I n other words, the conditions of changing acidity and sucrose tions of varying density the activity of the hydrogen ion increases concer$ration, both of which occur in the manufacturing with increasing sucrose concentration. operations, h a t e not been carefully duplicated in the experi6-When acid is added to impure sucrose solutions the various mental procedures, nor have the time and temperature salts and nonsugar compounds present function in varying degree factors been given proper consideration. as buffers, thereby governing the resulting activity of the hydrogen ion by altering the hydrogen-ion concentration which would In the work herein reported, laboratory procedures and otherwfse be obtained in pure solution. 7-The hydrolysis of salts in impure sucrose solutions, depend- improved analytical methods have been developed for studying upon the products of hydrolysis, may or may not increase ing inversion of sucrose during defecation of the juice, during evaporation of juice to sirup, during the operation of boiling the hydrogen-ion concentration. sirup to first massecuite, and during the boiling blank of sec1 Received October 6, 1924. 2 Brit. Assoc. Advancement Sci. Refits., 1906, p. 267. ond massecuite with subsequent use of a crystallizer. Since
A
INDUSTRIAL A N D ENGINEERING CHEMISTRY
52
the temperature and time of defecation vary in different factories, in accordance with the type of equipment and procedure in use, as likewise does the temperature for boiling massecuites, it has been impossible to make a complete study of all possible variations of these conditions within the time allotted to the present investigation. Certain definitely specified conditions known to exist commonly in practice have therefore been arbitrarily selected for the first experiments, and, as opportunity permits, other customary procedures will be similarly investigated. The material used for the experiments was sent to Washington from Louisiana. It was originally packed hot in 5-gallon cans, and after receipt was immediately placed in cold storage. Under these conditions it kept perfectly. Sulfur-lime juice and sirup, and also juice and sirup from a sugarhouse manufacturing raws, were obtained for the experiments. Procedure
DEFECATION OF JuIcE-hthough the juice obtained had already been clarified by the regular factory process, it was assumed that its composition resembled that of raw juice sufficiently for the purpose of the experiments. The pH value was adjusted as desired by the addition of sulfurous or phosphoric acid or milk of lime. Sulfurous acid was used in the experiments with SOZ-lime juice and sirup, while phosphoric acid was employed to increase the acidity of the limed juice and sirup (products defecated for raw sugar manufacture). In most of the defecation experiments the factory temperature duplicated was 100.5" to 93" C. (213" to 199.4"F.) over a period of 4 hours. The samples were first rapidly heated to boiling over a flame to duplicate the effect of passing the juice through a juice heater, and then placed a t once in an electric oven provided with a small motor-driven fan to equalize the temperature in different parts of the oven. The temperature of the juice was noted at intervals by means of a long-stem thermometer. Corresponding samples (510 cc.) of juice were weighed to an accuracy of 0.01 gram on a kilogram pulp balance. The 10 cc. which was pipetted into all 500-cc. portions, measured in a graduated flask, consisted of water plus the volume of acid or lime solution which was found necessary to give the desired p H value. Several samples were simultaneously placed in the electric oven; a t the end of the 4-hour period they were individually restored to their original weights by adding distilled water. In this way it was possible to compensate for evaporation of water and after the analyses to strike a sucrose, reducing sugar, and total sugar balance. Portions (10 cc.) of correqponding samples were titrated with 0.1 N sodium hydroxide solution using phenolphthalein as indicator and the pH was determined both before and after the heating period. Corresponding unheated samples were analyzed for the purpose of securing data which could be directly compared with the analyses of the defecated samples. COMBINED DEFECATION OF JUICE A N D EVAPORATION TO SIRUP-In these experiments an attempt was made to duplicate the factory operation of defecation as closely as possible and, without interruption for analysis, to evaporate juice to sirup, making the time and temperature of evaporation correspond to that which would obtain in a triple-effect evaporator. Since the period (4 hours) for the defecatian experiments described above was purposely somewhat exaggerated, it was decided in these combined defecation and evaporation experiments to limit the period in the oven (temperature 96" to 94" C.) to 2 hours, and then evaporate the same juice to sirup. A laboratory triple-effect evaporator not being available, use was made of a single-effe~t,~ which was emDesigned by F. W. Reynolds of this laboratory, Chem. Met. Ens., 80, 585 (1924). 8
Vol. 17, No. 1
ployed subsequently for boiling the sirup to massecuite. The total time allowed for evaporation in the single-effect evaporator was 1 hour and 45 minutes. During the first 35 minutes the temperature was 82" C. a t 368 mm. (14.5 inches) of vacuum, for the second 35 minutes 71" C. a t 521 mm. (20.5 inches) vacuum, and for the third 35 minutes 60" C. a t 622 mm. (24.5 inches) vacuum. Although this is only an approximation of the operation of a triple-effect evaporator, it represented a control of time and temperature which yielded a 50" Brix sirup when starting with juice a t 15" Brixfor the defecation. The volume of juice placed in the electric oven for each sample was 4 liters, which yielded about 1000 cc. of sirup a t approximately 50" Brix, or enough to cover the hottest portion of the steam coil a t the end of the evaporation. In these experiments acidities a t the beginning and end of the operation were determined and analyses were made, as will be described. BOILINGSIRUP TO FIRSTMAssEcurTE-For the experiments duplicating this stage of the factory process, the time taken for a strike was 4.5 hours. The maximum temperature was 73" C. for graining, the minimum temperature 67" C., and the average temperature 69" C. Although a lower range of boiling temperature is commonly employed, many sugar boilers prefer to operate the vacuum pan at this temperature, and it seemed advisable in the initial experiments to determine maximum inversion effects. Use was made of the vacuum pan mentioned above. Approximately 14 liters of 50" Brix sirup are required for boiling a full strike of sugar in this pan. Samples of sirup with varying pH values were boiled to massecuite and corresponding analyses were made of both sirups and massecuites to determine the extent of inversion. The sugar resulting from these boiling experiments was washed with a little water in a laboratory sugarhouse type Centrifuge to ascertain by way of interest the approximate quality of sugar which might be expected under factory conditions. SECOND MASSECUITE AND CRYSTALLIZER EXPERIMENTSI n another experiment use was made of a synthetic product prepared by adding sugar to molasses, adjusting the pH value to correspond to the maximum resulting from the sirup boiling experiments, then boiling this product blank in the vacuum pan and subsequently transferring it to the laboratory ~rystallizer.~The apparent purity of this molasses was 60, the average temperature in the pan was 60" C., and a 2-hour period was required to concentrate from 54.4" to 91.2O Brix The period in the crystallizer was 4 days, the temperature being reduced during this time a t a definite gradient from 60" to 35" C. The analytical results are given in the tabulated data which follow. Analytical Methods
In studying inversion under varying conditions, apparent purity is obviously not a reliable index; even the true purity determination must be carefully inspected with regard to error involved. Preliminary analysek of approximately 15" Brix juice showed that in determining total solids by drying in a vacuum oven a t 70" C. the maximum absolute difference for many values for the percentage of total solids was 0.03 per cent. Determination o€ "true sucrose" by means of the precise invertase method, under carefully controlled conditions, gave percentages with an absolute maximum variation of 0.025 per cent. N o t e " T r u e sucrose" is the percentage of sucrose in the sample as determined by the method of double polarization. "True purity" is the percentage of sucrose in the total solid material (determined by drying). These 4 This crystallizer, equipped for crystallization in motion with close control of temperature gradient, was designed by F. W. Reynolds of this laboratory, loc. c i t .
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1925
terms are customarily employed in sugarhouse control in contradistinction to “apparent sucrose” and “apparent purity.” “Apparent sucrose” is the direct polarization of a normal weight of sample, while “apparent purity” is the ratio of apparent sucrose to apparent total solids as determined by the Brix hydrometer.
Similar analysis of high-density products, such as sirups and massecuites, has shown an absolute maximum variation of 0.1 per cent in the values for true sucrose and 0.07 per cent in the values for total solids. If the value found for true sucrose is too high and that for total solids is too low, or vice versa, by the maximum variation stated, the resulting true purity value may be in error by as much as 0.8 and 0.5 for juice and sirup samples, respectively. However, as indicated by the data reported, the experimental error has usually been considerably less. Values for “glucose” for a given sample of cane juice, it was found, should show an absolute variation of not more than 0.01 per cent. From this it may be calculated that values for the glucose ratio for a given sample of juice containing 12 to 13 per cent sucrose should not show an absolute variation greater than 0.20 to 0.26; for a given sirup sample the determined values for percentage of glucose should not differ by more than 0.05 (absolute) and the absolute maximum variation in glucose ratio should not be greater than 0.20. Nole--In cane sugar manufacturing practice the total reducing substances in the factory products consisting principally of dextrose and levulose are usuallv termed “rrlucose.” The word “alucose” is therefore used in this ,,-per cent “glucose” X 100, sense in the present paper. “Glucose ratio per cent sucrose
-
The Meissl and Hiller method for determining reducing sugar gravimetrically was considered most suitable for the purpose. To samples taken both before and after the heat treatment a little anhydrous potassium oxalate was added to precipitate the calcium of the lime salts, a little pre-washed kieselguhr was added, and the solution was filtered. A sample that would yield from 0.25 to 0.35 gram of cupric oxide was taken. I n order to secure the maximum possible sucrose concentration in the analysis of juice samples, Horne’s method of clarification was followed. Weighed quantities of dry lead subacetate were added to measured portions of the samples, and
Expt.
1 2
...
...
7.10 7.10 6.50
6.65 6.30
0.15 0.25 0.40
0.35 0.50
7.10 6.70 6.10
7.00 6.50 6.10
0.25 0.45 1.05
0.35 0.50 1.05
Blank 8.25 Blank defecated 8 . 2 5 Sample +Hap04 6 . 6 5
6.50 6.50
Neutral 0 . 3 5 0.35 0.40
+ +
3
preparation were added, and the solution was diluted to the mark and polarized in a 4-dm. jacketed tube a t 20” C. on the following morning. In the analysis of high-density products (sirups and massecuites) the normal weight method was used for direct polarization and true sucrose determination. The solutions were clarified with Horne’s dry lead subacetate, after diluting to volume. This procedure eliminated the error due t o volume of lead precipitate, making the results comparable with those obtained by using the dry lead subacetate method for the juice analysis. The procedure after the filtration of the lead precipitate was the same as that described for the juice. I n determining total solids, 10 cc. of solution, containing approximately 1 gram of solids, were mixed with about 35 grams of 30- to 40-mesh sand, evaporated on a steam bath with stirring and heated for 20 hours a t 70” C. a t 660 to 711 mm. (26 to 28 inches) vacuum, a slow current of dry air being drawn through the oven. I n the defecation experiments a comparison of the percentage of sucrose before and after heating in the oven was a valuable criterion of inversion. Also, by diluting all samples to initial weight with water after defecation, it was possible to determine a suorose and total sugar balance, which was useful not only in checking the glucose ratio, but also in showing when destruction of invert sugar occurred. Although useful in indicating the extent of inversion, the glucose ratio is not an absolute criterion, owing to the fact that slight sucrose inversion may occur simultaneously with destruction of invert sugar, or change in its reducing power, in which case inversion might not be detected. I n the sirup-boiling experiments it was not feasible to determine a sucrose balance, but analyses of the sirup and corresponding massecuit,e,making use of both true purity and glucose ratio determinations, furnished decisive data. For example, in order to conclude definitely that inversion had occurred in boiling sirup to massecuite, it would be necessary to find both an increase in glucose ratio and a decrease in true purity by an amount greater than the experimental error. Early in the investigation it became apparent that it is difficult to make a precise determination of pH in sugarhouse
TABLE ‘I-DEFECATION OF JUICE ACIDITY (Cc. 0.1 N NAOH PER 10 Sucrose COLORIMETRIC PH Cc. OF SAMPLE) Direct by inAfter Before After ‘Brixby polari- vertase Glu- GluBefore defeca- defeca- defeca- defeca- hydrom- zation method cose cose MATERIAL tion tion tion tion eter V. % % ratio Blank Blank defecated Sample+HtPOa Blank h o t analyzed) Blankdefecated Sample HsPOa Sample HsPOa
53
Weight Calcd. of glu- to sucose and crose -WBIQHTsuequiva- Lossof Juice Sucrose Glucose crose lent sucrose Grams Grams Grams Grams Grams %
Limed Juice 1 5 . 0 0 , 11.83 12.21 0 . 9 8 3 8.059 534.39 65.249 15.00 11.83 12.20 0.987 8 . 0 9 0 534.59 65.220 15.00 11.81 12.19 1.020 8.367 534.42 65.148
15.00 15.00 15.00 15.50 15.50 15.50
11.83 11.79 11.75 11.96 11.97 11.91
12.18 12.15 12.13 12.28 12.25 12.25
534.27 634.73 534.92 534.50 534.53 534.80
5.253 5.276 5.451
65.074 5.343 64.970 5.486 64.886 5.627 65.637 5.131 65.480 5.105 65.513 5.321
1.000 1.026 1.052 0.960 0.955 0.995
8.213 8.444 8.673 7.817 7.796 8.122
0.734 0.736 0.745 basis of
6.076 479.00 57.863 3.516 6.093 478.92 57.854 3.525 6 . 1 7 2 479.10 57.827 3.569 the “blank defecated.”
70.502 70.339 70.496 70.232 d.‘d4 70.599 70.336 0 . 1 5 70.417 70.456 70.513 70.768 70.585 70.830
70.150 70.182 d.i‘6. 70.232 0.29O 70.511 70.330 O.*i4 70.568 0.19
Sulfur-Lime Juice 4
Blank 6.90 0.60 14.53 11.80 1 2 . 0 8 Sample Hap04 6 . 8 0 0.60 14.53 11.79 12.08 Sample HsPO4 6 . 7 0 0.65 14.53 11.79 12.07 a The blank was not analyzed and the sucrose losses have been calculated on the
++
.. . ...
.. .
...
after filtration weighed quantities of the deleading agent, ammonium dihydrogen phosphate, were added, and the solutions were refiltered before determining the direct polarization (in jacketed 2-dm. tube a t 20” C.). The invertase method, employing the inversion constant corresponding to existing sucrose concentration, was used for precise determination of sucrose. A 50-cc. portion of the deleaded solution used for the direct polarization was placed in a 100-cc. graduated flask, 5 cc. of a concentrated, standardized invertase I
61.379 61.203 61.379 61.203 O’.bi 61.369 61.218 0.06
samples. The presence of salts and various organic compounds other than sugar in cane juice and sirup has a disturbing effect on both the electrometric and colorimetric methods. Experiments with the hydrogen electrodes indicated that especially in sulfur-lime samples reliable data were not being secured. The long period required t o saturate the sample with hydrogen also constituted a serious objection to the hy-
*
The authors gratefully acknowledge the assistance of I,. E. Dawson of this laboratory in connection with electrometric p H determinatidns.
INDUSTRIAL AND ENGINEERING CHEMISTRY
54
drogen electrode. A device for atomizing the gas greatly reduced the saturation time, but even this procedure was relatively unsatisfactory. It is also possible that the pH value of the samples may have been altered as a result of absorption of the large quantities of hydrogen and of resulting change in acid-base equilibrium. The hydrogen electrode was therefore abandoned and use was made of the colorimetric
Vol. 17, No. 1
frequently to check the color standards for the various indicators by means of standard buffer solutions, and to substitute fresh standards promptly when required. For work of the greatest precision, the effect of various salts on the indicators used for colorimetric hydrogen-ion measurements should be taken into consideration.9 For the purpose of these experiments on inversion, however, using the
TABLE 11-DEFECATION O F LIMED JUICE^ ACIDITY(Cc. 0.1 N NAOH PER 10 COLORINMETRIC PH Cc. OF SAMPLE)O Brix Before After Before After by hydefeca- defeca- defeca- defeca- dramExrJt. MATERIAL tion tion tion tion eter 1 Blank 7.10 0.26 . . . 17.90 Blank defecated 7.10 6.30 0.25 0.60 17.90 Sample 6.10 5.90 1.05 L25 17.90 Sample HsPOi 5.70 5.70 1.65 1.70 17.90 2 Blank 8.25 ... Neutral 15.50 Blankdefecated 8.25 6.35 Neutral 0.60 15.50 Sample+HsPOa 7.15 6.15 0.25 0.80 15.50 Sarnde+HsPOa 6.65 6.15 0.35 0.83 15.50 3 Blank 8.25 Neutral 15.00 Neutral 1.80 15.00 Blankdefecated 8.25 0.40 1.65 15.00 ... Sample HsP04 6.65 .,, ‘0.20 1.70 15.00 Sample H3P01 7.15 a Unusual conditions. See Discussion.
...
+
~~
1
...
...
.
...
+ +
...
WEIGHT
Sucrose Direct by inpolari- vertase Gluzation method cose V. % %
13.97 13.91 13.68 13.48 11.96 11.73 11.14 11.37 11.81 5.73 7.71 7.14
method. Dawson6 found that results obtained by use of the quinhydrone electrode agreed well with those obtained by the colorimetric method in the case of cane products which did not contain free sulfurous acid and which were diluted to 15” Brix. I n all the experiments reported in the tables the p H value given was determined by the colorimetric method. All samples were diluted to the same density (15” Brix) with fteshly boiled distilled water, testing pH = 7.0. Under these conditions the colorimetric method was rapid and was considered to give reliable data. The procedure employed was essentially Gillespie’s “block comparator” method,’ which is more accurate than the spot plate method commonly used for colorimetric determinations. The color intensity in the “block comparator’’ method is less than that in the spot plate procedure; it is an advantage, also, to make allowance for the natural color of the sample plus added indicator, as is done in Gillespie’s method. Hatfield’P modification of Gillespie’s method represents an improvement, in that standards prepared with buffer solutions are much more permanent, retaining their original color for about a month if the precau-
14.46 14.42 14.22 14.08 12.26 12.01 11.55 11.76 12.19 7.02 8.71 8.20
Glucose ratio
1.172 1.225 1.446 1.545 0.965 1.133 1.632 1.485 0.990 5.925 4.358 4.819
8.105 8.495 10.169 10.973 7.871 9.434 14.130 12.628 8.121 84.402 50.034 58.768
Y
Glu-
Calcd. to sucrose equiva- Lossof lent sucrose Grams %
Juice Grams
case and Sucrose Glucose sucrose Grams Grams Grams
540.70 540.71 540.72 540.77 534.50 534.61 534.50 534.10 534.60 534.73 534.50 534.52
78.185 6.337 84.552 84.205 77.430 6.624 84.045 83.723 0.97 76.890 7.819 84.707 83.318 1.6ti 76.140 8.355 84.495 84.077 65.530 5.158 70.688 70.430 2.62 64.207 6.057 70.264 69.961 2.02 61.735 8.723 70.458 70.022 5.79 62.810 7.931 70.741 70.344 4.15 65.168 5.293 70.461 70.196 37.538 31.683 69.221 67.637 42140 46.565 23.294 69.849 68.684 28.56 43.831 25.759 69.590 68.302 32.74
...
...
series of indicators recommended by Clark and Lubs,Qit was considered that less error resulted from the effect of salts on the indicators than was found to occur from a similar cause or by “poisoning” of the electrode in the electrometric method. I n nearly all cases it was possible to determine the p H value of samples by means of two overlapping indicators, the values usually agreeing within 0.1 pH. Experimental Data Tables I to VI record the experimental data so far obtained. The data reported are averages of duplicates which agreed within the limits of observed experimental error. Discussion
Referring to Table I, and allowing for maximum experimental error, as already discussed, inversion during the defecation of limed juice is not definitely apparent until the initial p H of the juice is reduced to 6.1. I n Experiment 2, Table I, the per cent sucrose decreased from 12.18 to 12.13, a difference sufficiently greater than experimental error to justify the conclusion that inversion had occurred; confirmation is
TO SIRUP TABLE 111-COMBINEDDEFECATION i3~ JUICE AND EVAPORATION
MATERIAL
Colorimetric PH
Juice Sirup Juice Sirup Juice Sirup
6.90 6.50 6.90 6.50 7.07
Juice Sirup Juice Sirup Juice Sirup Juice Sirup
5.90 5.90 6.45 6.20 6.20 6.20 6.70 6.50
6.60
Acidity (cc. 0.1 A’ NaOH per 10 cc. of samples at 15O Brix)
O Brix by hydrometer
0.28 0.40 0.30 0.38 0.20 0.33
14.95 53.45 14.75 37.50 14.45 46.70
1.25 1.05 0.85 0.90
15.00 56.08 15.00 52.20 15.20 55.41 15.28 57.94
... ...
0.75 0.85
Solids by drying
%
Direct polarization
v.
Sucrose by invertase method
%
Limed Juice to Sirup 14.16 11.51 11.86 51.96 42.45 43.31 11.45 11.81 14.11 29,85 30.58. 36.47 11.52 13.75 11.19 45.43 37.05 38.07 Sulfur-Lime Juice to Sirup 14.49 10.70 11.19 41.54 54.25 39.69 11.37 14.49 10.93 38.25 39.95 51.11 11.25 14.49 10.67 41.60 53.69 39.60 11.33 14.54 10.72 43.69 56.13 41.73
tion is taken to add a few drops of toluene to the tubes and to paraffin the corks. It was considered advisable, however, e I ,. E. Dawson expects to publish his results with the quinhydrone electrode soon. 7 J . Am. Chem. Soc., 42, 742 (1920): Soil Science, 9, 115 (1920). e J . Am. Chem. Soc., 46, 940 (1923).
Apparent purity
True purity
Glucose
%
Glucose ratio
%
%
0.973 3.630 0.973 2.531 0.944 3.105
8.221 8,381 8,239 8.277 8.191 8.164
76.99 79.42 77.66 79.60 77.44 79.34
83.76 84.51 83.68 83.84 83.81 83.80
2.175 8.425 1.960 7.068 1.953 7.361 1.961 7.615
19 437 20.282 17.236 17.692 17.360 17.695 17.308 17.430
71.35 70.77 72.86 72.72 70.20 71.47 70.16 72.02
77.23 76.57 78.47 78.16 77.63 77.48 77.92 77.84
found in the increase of the glucose ratio from 8.213 to 8.673. I n Experiment 1, Table I, the per cent sucrose decreased from 12.21 for the blank to 12.19 for the sample of which the pH was 6.5. Although this difference is not in excess of experi-
* Clark, “The Determination of Hydrogen Ions.”
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
January, 1925
mental error, the glucose ratio increased from 8.059 to 8.367. Moreover, in Experiment 3 the sample of initial pH 6.65 and in Experiment 2 the sample of initial pH 6.7 showed the maximum decrease in sucrose attributable to experimental error, and likewise the maximum increase in glucose ratio. Although a single experiment might not furnish conclusive evidence, since the variation in per cents sucrose and glucose during
MATERIAL Sirup Massecuite Sirup Massecuite Sirup Massecuite
Colorimetric pH
6.50 6.50 6.70 6.60 7.00 6.80
Acidity (cc. 0.1 A’ NaOH per 10 cc. bf of sample a t 15’ Brix)
... ... 0.32 0.32 0.20
...
55
even greater degree of inversion because juice samples were kept in the oven lor 40 hours and the concentration was increased by evaporation to approximately that of a thin sirup. I n all the defecation experiments the increase in p H determined colorimetrically was readily detectable, the greatest change being apparent in those samples in which the initial
TABLE IV-RESULTS OF SUGAR BOILINGEXPERIMENTS O Brix by Solids by hydromdrying eter %
47.20 46.86 57.35 47.06 54.14 45.56
Direct polarization
v.
Sucrose by invertase method
70
Glucose
%
Raw Sugar Sirup to Massecuite 45.85 . 37.65 38.74 3.157 45.61 55.82 45.93 52.48 44.07
37.25 45.74 37.62 43.25 36.22
35.19 46.95 38.47 44.21 37.11
3.118 3.804 3.146 3.494 2.983
Glucose ratio
Apparent purity
Yo
True purity
%
8.149 8.164 8.102 8.178 7.901 8.038
79.77 79.49 79.76 79.94 79.88 79.50
84.49 83.73 84.11 83.76 84.24 84.21
17.086 17.002 17.289 17.234 17.235 17.149 17.371 17,203 4.683 4.680
72.52 72.61 72.46 73.13 72.86 73.09 72.55 72.78 84.95 86.13
78.46 78.57 78.47 78.61 78.47 78.56 78.26 78.39 87.12 87.20
REMARKS Double diluted Double diluted Double diluted
Sulfuv-Lime Sivup 20 Massecuite Sirup Massecuite Sirup Massecuite Sirup Massecuite Sirup Massecuite Sirup Massecuite
6.00 6.25 6.05 6.30 6.45 6.50 6.80 6.85 6.90 6 90
1.32 0.90 1.30 0.90 0.85 0.75 0.55 0.55
... ...
53.05 46.96 55.95 47.22 56.00 47.20 55.20 47.87 58.68 88.56
51.44 45.38 53.97 45.73 54.43 45.76 53.43 46.42 58.21 87.48
38.47 34.10 40.55 34.53 40.80 34.50 40.05 34.84 49.85 75.30
defecation in these experiments was always in the same direction, it is apparently safe to conclude that the border line close to which a slight degree of inversion takes place is approximately p H 6.7. Referring to Experiment 4, Table I, the conclusion seems warranted that no inversion occurred in the defecation of sulfur-lime juice. I n the experiments listed in Table I1 unusual conditions obtained. I n Experiment 1 the initial apparent solids content was 17.9’ Brix instead of approximately 15’ Brix, as for the experiments reported in Table I. Although only one experiment a t this density is reported, the data indicate that some inversion occurred even in the sample designated “blank defecated” which possessed an initial p H of 7.1. Although it is not safe to conclude from the results of one experiment that increase in degrees Brix from 15 to 17.9 is solely responsible for the observed inversion a t higher pH, it is true that the inversion velocity increases a t higher sucrose concentrations. I n Experiment 2, Table 11,the conditions differed markedly from those applying to the experimenfs in Table I, in that the period in the oven was purposely increased to 18 hours to approximate roughly the temperature condition which would obtain in the defecation of juice by use of the Dorr clarifier. In operating this clarifier it is estimated that, although most of the juice remains in it for a comparatively short time, possibly 6 per cent of the total volume handled is retained for as long as 18 hours and possibly as much as 2 or 3 per cent remains in the clarifier for an even longer period, this juice being that which remains in the bottom of the clarifier before the muds are drawn off. It has been observed in practice that juice becomes more acid the longer it remains a t a relatively high temperature, and the results of this experiment show that the pH decreased from a value as high as 8.25 to one of 6.35 a t the end of the IS-hour period. The inversion in this experiment was undoubtedly greatly in excess of experimental error. The density of the juice, however, increased somewhat owing to evaporation, and it cannot be concluded that the same degree of inversion would occur in ordinary practice. I n order to determine this question more definitely it is necessary to repeat the experiment, taking care that no appreciable evaporation occurs. Experiment 3, Table 11, shows an
40.36 35.66 42.35 35.95 42.71 35.95 41.81 36.39 50.71 76.28
6.896 6.065 7.322 6.194 7.361 6.165 7.263 6.178 2.375 3.570
Double diluted Doublediluted Doublediluted Double diluted
titrated acidity was smallest and the p H correspondingly highest. This is shownin Experiment 3, Table I, and in Experiment 2, Table 11. As an explanation of this increase in acidity, the theory may be advanced that a greater destruction of glucose and possibly of other substances in the juice takes place with the formation of acid products when the samples are originally close to phenolphthalein neutrality than when they are somewhat more acid in reaction. The data reported in Table I11 indicate that, in the combined defecation of limed juice and evaporation to sirup under conditions comparable to the factory practice described under “Procedure,” no degree of inversion greater than that attributable to experimental error can be inferred. The p H value, however, was practically the same in all these experiments with limed juice, and it is desirable also to secure data for samples having a higher initial acidity. I n the experiments on defecating sulfur-lime juice and evaporating it to sirup, inversion was clearly indicated when the initial pH was 5.9 and the titrated acidity 1.25, the glucose ratio increasing and the true purity decreasing by amounts greater than the experimental error. Some inversion is also indicated in those experiments in boiling SOz-lime juice to sirup when the initial p H values for the juice were 6.20 and 6.45, respectively. When the p H value of the juice was 6.7 little inversion, if any, occurred. The results of the sugar boiling experiments reported in Table I V indicate that in boiling raw sugar sirup to massecuite inversion takes place when the pH of the sirup (measured a t 15 O Brix) is as high as 6.5, the true purity decreasing from 84.49 to 83.73-that is, by more than the experimental error. Agreement between true purities is exceptionally close in the experiment in which the p H of the sirup is 7.0, and in this case no inversion is indicated. When the p H value of the sirup is 6.7 the decrease in true purity is some what less than the experimental error, being only 0.35, but this decrease is intermediate between the results of the other two experiments. It is possible to explain the close agreement in glucose ratios on the assumption that slight destruction of glucose occurred during the experiment. Comparing the data of these three experiments, the pH value 6.7 for raw sugar sirup appears to represent the boundary line a t which
I N D U S T R I A L A N D ENGINEERING CHEMIXTRY
56
there is only slight inversion, if any, but below.which inversion becomes definitely apparent. In the experiments on boiling sulfur-lime sirup to massecuite, also reported in Table IV, no inversion occurred, even when sirup of pH value as low as 6.0 was used. I n TableV two experiments are recorded in which sulfur-lime sirup a t approximately 50" Brix was boiled a t atmospheric pressure
Vol. 17, No. 1
In boiling sirup to massecuite the acidity is greater than that of the juice from which the sirup is derived, although, of course, the temperature is lower than during defecation. If boiling raw sugar sirup of pH 6.7 measured a t 15" Brix, corresponding to pH 6.35 a t 50" Brix, gives results indicative of inversion, it is obviously not necessary for the purpose of this investigation to study the defecation of juice of
TABLEV-RESULTS OF BRUSHPAN EXPERIMENTS (SULFUR-LIME SIRUP)
MATERIAL Sirup original Sirup: heated Sirup, original Sirup, heated
Colorimetric PH 6.80 6.60
5.95 5.90
Acidity (cc. 0.1 N NaOH per 10 cc. of sample a t 15' Brix)
Brix by hydrometer
0.55 0.62 1.45 1.25
55.20 66.50 56.68 56.92
Direct polarization
Solids by drying
Sucrose by invertase method
v.
% 53.42 54.80 55.09 54.99
%
40.05 41,22 41.15 40.61
41,81 43,OO 43.05 42.46
Glucose
%
Glucose ratio
7.268 7.427 7.579 8.255
17.371 17.272 17.605 19,442
ADvarent phrity
True purity
72.55 72.96 72.60 71.35
78,26
%
%
7s.47 78.14 77.21
TABLE VI-BOILING 60 PURITYMOLASSES BLANK MATERIAL Molasses Massecuite
Colorimetric PH
5.90
...
Temperature in crystallizer
Acidity (cc. 0.1 N NaOH)
Brix by hydrometer
Solids by drying
%
Direct polarization
Sucrose bv invertasemethod
Glucose
31.55 54.73
33.81 57.55
7.12 12.05
... 54.44 50.79 ... 91.22 85.82 After 24 hours 53.5' C. 2: : ~ $:: ~ ~ After 4 days, 35.0°C.
v.
for 15 minutes, and subsequently kept on the steam bath for 4 hours to duplicate approximately the practice of "cleaning" the sirup in a brush-pan in those factories operating to produce first sugar and a high grade of first molasses. No inversion occurred when the pH value of the sirup was 6.8 and the titrated acidity 0.45, whereas, when the pH of the sirup was 5.95 and the titrated acidity 1.45, the increase in glucose ratio and decrease in true purity clearly indicated appreciable in yersion. Table VI gives the results of an experiment on boiling molasses blank and then plwing it in a crystallizer. The pH value of this material, measured a t 15" Brix, was 5.9, which is as low as in any samples of molasses resulting from the sugar boiling experiments in which no inversion occurred. The close agreement between both the glucose ratio and true purity for molasses and the resulting massecuite indicates that no detectable inversion occurred during this experiment. Whenever the quinhydrone electrode was used to determine the pH value of samples of sirup directly, without diluting below 40"Brix, the pH value found was always lower than that for the same sample after dilution to 15" Brix. A variation from pH 6.36 for sirup a t 46" Brix to pH 6.61 for the same sirup a t 15" Brix represents a typical difference. This variation probably represents the net result of differences in acid concentration and dissociation and likewise of hydrogenion activity, since the volume concentration of both acid and sucrose is greater a t the higher Brix. This relation should be kept in mind in factory procedures during which water is progressively evaporated.
%
%
Glucose ratio
Apparent purity
21,059 20.937
%
57 I95 BO. 00
True purity
%
66.57 67.OR
such initial pH that it will yield sirup of the p H value mentioned. It would seem rather that the initial pH value of the juice should be such that when this same juice is evaporated to sirup, the sirup can be boiled to massecuite without inversion. Reasoning along this line, the data obtained indicate that, in defecating juice for raw sugar manufacture, the inital pH at which it is safe to carry the juice lies between 7.0 and 8.0;'o in other words, a t such a point that this juice, when evaporated to sirup, will possess a pH (measured a t 15" Brix) lying between 6.7 and 7.0. I n the sulfitation process, by which direct consumption sugar is produced, it is indicated that a lower pH and correspondingly higher titrated acidity may be safely carried. The sulfites present in these sugarhouse liquors apparently retard the progressive increase in acidity by the decomposition of glucose, and may also possess a specific inhibiting property in the inversion of sucrose. Investigation of the specific influence of sulfites on p H measurement (both colorimetric and electrometric) is required for fuller explanation of this matter.
.............. A selected bibliography of literature on the inversion of sucrose and the determination of hydrogen ion has been prepared by the authors, who will be glad to furnish copies upon request. Space does not permit publication of this bibliography in connection with this article. 10
This is in substantial agreement with McAllep's conclusions, Louisi-
ana Plantev, 73, 114 (1924).
Work of Bureau of Mines Discussed in Annual Report Accidents in the coal mines of the United States continue a t a f a r too frequent rate, according to the annual report of the Bureau of Mines. Efforts have been made to increase safety in mining by the development of international cooperation with the Mines Department of Great Britain, and an extensive campaign for the adoption of rock dusting as a preventive of disastrous explosions in bituminous coal mines.
A lignite carbonizer designed by the bureau should result in the ultimate solution of the tremendously important problem of economic utilization of the lignites of the Northwest, which comprise nearly one-third of our total solid fuel resources. The use of cooling systems in vapor-tight tanks in which crude oil is stored should check evaporation losses of gasoline, which
amount annually to 3 or 4 per cept of the stocks accumulated during the winter season, and whose value runs into millions of dollars. A laboratory for radium research has been established in Washington. Important fuel economies in the operation of industrial kilns manufacturing brick, tile, and other heavy clay products have been made possible by a study of the burning problems of such kilns. At the request of the Commission of Gold and Silver Inquiry of the United States Senate, a study of new uses for silver has been undertaken. The purpose of the study is to increase the demand for the metal, and thereby aid the western silver mining industry, which has for several years faced unfavorable economic conditions.
