I N D U S T R I A L A N D ENGINEERING CHEMISTRY
282
the same percentage of burbot-liver oil gave good signs of healing. With as low as 0.015 per cent burbot-liver oil addition to the ration there were still considerable signs of healing. The two rats on the 0.007 per cent burbot-liver oil were probably comparable to the 0.06 per cent cod-liver oil addition. There seems t o be no doubt that the samples of cod- and burbot-liver oil studied showed a marked difference in antirachitic potency. A quantitative estimation of the comparison revealed that the burbot-liver oil is eight times as potent as the cod-liver oil. For instance, the 0.06 per cent burbot-liver oil and the 0.5 per cent pod-liver oil rations give healing (see table) and the latter has practically eight times the amount of oil addition; 0.03 per cent burbot-liver oil and 0.25 cod-liver oil give healing, etc. Whether or not this difference in antirachitic potency is ++++
VOl. 21, N o . 3
due to the inherent property of the oils or to a variation from one sample t o another is not known. Hess, Bills, Weinstock, Honeywell, and Riokin4 have reported a wide variation in the potency of cod-liver oil. They report that the antirachitic potency of the liver of the cod is in inverse ratio to its content of oil. Tests of the ether extract of livers, very small and poor in fat, showed them to be exceptionally potent-"far exceeding in potency any oil which has been heretofore reported." In the light of this work by Hess and his co-workers, perhaps too much emphasis may be placed on the relative potency of burbot- and cod-liver oils. At least, we probably can assume that burbot-liver oil may be classed with cod-liver oil as an excellent source of the antirachitic vitamin.
+ + +
4
Hess e t al., Proc. SOC.Ezptl. Biol. Med., 26, 653 (May, 1928)
Inversion of Sucrose in Beet-House Sirups' R. J. Brown and H. W. Dahlberg GREATWESTERN
S C C A R COMPANY,
DENVBB, COLO.
A satisfactory method for the determination of the quantity of copper reinvert sugar in beet-factory sirups has been given. duced by a given quantity of adoption of p H conIt has been shown that the invert-sugar content of invert sugar by this method trol in beet-sugar low-purity beet products cannot be taken as a measure varies with the temperature factory operations, replacing of previous inversion of sucrose, owing to the destruca t the boiling point, which the former control by alkation of invert sugar in such products. In the range a t high altitudes is lowered linity, the problem of inverof 6 to 9 pH the rate of destruction of invert sugar was sufficiently to cause a decided sion of sugar has become imfound to depend on the concentration of impurities, decrease in reduced copper. portant. the H- or OH-ion concentration showing no measurable After studying various proSince the published data on effect. cedures, many of which had rates of inversion of sucrose The effect of various factors on the rate of loss of been proposed by p r e v i o u s i n s i r u p s conflict in some sucrose in beet sirups was roughly determined. Deinvestigators, the f o 11owing cases, a brief investigation of creasing the pH of the sirup from 8 to 6 increased the method was adopted as one the inversion p r o b l e m w a s rate of loss of sucrose about ten times. Decreasing which would give concordant made for the purpose of dethe purity from 100 to 60 per cent decreased the rate of results: t e r m i n i n g the approximate loss of sucrose about 40 per cent. A 10"C. temperature rate of destruction of sucrose Transfer a quantity of sirup rise increased the rate from two to three times. Variaunder conditions met in pracrepresenting 11.0 grams of dry tions in concentration of solutions, in the range of tice. The field covered insubstance t o a 200-ml. flask, 10 to 80 per cent dry substance, produced no marked cluded the development of a clarify with the minimum quaneffect on the rate. The rate of loss of sucrose in beet tity of neutral lead acetate, and satisfactory method for defilter. Delead 100 ml. of the sirups from different sources was found to be constant, termination of invert sugar in filtrate with 10 ml. of a solution under constant conditions. The rate of loss of subeet-sugar products, the ascontaining 5 grams each of socrose in sirups of 90 per cent purity at 6 pH and 80 certaining of the suitability dium oxalate and d i s o d i u m per cent dry substance heated at 80" C. was almost p h o s p h a t e per 100 ml., and of the invert sugar determinafilter. Transfer 50 ml. of this double that calculated by Spengler a'nd Todt on the tion as a measure of sucrose filtrate to a 250-1111, Erlenmeyer basis of the inversion constant of sucrose in hydrod e s t r o y e d , and the deterflask, add 50 ml. of mixed Fehlchloric acid found by Jackson and Gillis. m i n a t i o n of t h e r a t e a t ing's solution (Quisumbing and Thomas modification2), cover which sucrose was destroyed. These three phases of the problem will be considered sepa- with a watch glass, and heat in a water bath a t 80' C. for 30 minutes. Filter the reduced copper through asbestos in a rately. Gooch crucible and determine copper by the iodine m e t h ~ d . ~
ITH t h e g e n e r a l
Determination of Invert Sugar in Beet Sirups
The difficulty in making the invert sugar determination in low-grade beet products arises from their low invert-sugar content, usually less than 1 per cent on dry substance. I n the ordinary method, where 50 ml. of clarified solution, representing 10 grams of sirup dry substance, are boiled with 50 ml. of Fehling's solution for 2 minutes, the cuprous oxide precipitate is frequently very unsatisfactory, and duplicate analyses often fail to give concordant results. Furthermore, 1 Presented before the Division of Sugar Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
Calculate invert sugar from the Quisumbing and Thomas tables, making corrections for effect of sucrose.
The Quisumbing and Thomas method of copper reduction was adopted because their temperature of heating could be reproduced, and because rather extensive tables were available. The covered Erlenmeyer flask was used since it was found that the exclusion of air during the heating period was the determining factor in preventing the formation of a highly dispersed copper precipitate. Since the concentration of sirup impurities is also a factor in determining the degree of 2
8
Quisumbing and Thomas, J. Am. Chcm. Soc., 48,1503 (1921). Assocn. O5cial Agr. Chem., Methods, p. 191 (1925).
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1929
dispersion and purity of the copper oxide precipitate, the size of sample taken may be increased as the purity of the sirup to be analyzed is increased. The use of the oxalatephosphate mixture as a deleading agent4 instead of sodium carbonate also improved the purity of the copper precipitate and increased the accuracy of the iodine titration. Unfortunately no method is available for determining the invert-sugar content of a complex product, such as beet molasses, with certainty; and the copper-reducing power is considered synonymous with invert-sugar content. Therefore, a satisfactory method a t present is one which will yield concordant results in duplicate analyses and one which contains no obvious faults. I n this investigation a variation in invert-sugar content of low-purity sirups was found when various methods of preparing the sample were used. A reduction in the quantity of sample taken lowered the observed invert-sugar content of the sirup. The use of clarifying agents also decreased the observed value. The effect of various methods of preparation of the sample on the true invert-sugar content was determined in the following manner: The invert-sugar content of a sirup was determined, using various methods of preparation of the sample. Known quantities of invert sugar were then added to the sirup. and the invert-sugar content of the mixture was determined by the various procedures used on the original sirup. With certain methods the quantity of invert sugar found in the mixture checked the calculated quantity. I n other cases the determined value was lower than the calculated, owing to a removal of invert sugar during preparation of the sample. Clarification of the sample with basic lead acetate or with decolorizing carbons, both of which improve the quality of the copper precipitate, lowered the invert-sugar content of the sample. Neutral lead acetate with either sodium carbonate or the oxalate-phosphate mixture had no effect on the invert-sugar content. The method adopted was the one which gave the minimum invert-sugar content in the original sirup and a t the same time did not change the actual invertsugar content-in other words, the one in which the influence of copper-reducing non-sugars was a t a minimum. Table I gives the results obtained on one sample of molasses, adding various known quantities of invert sugar, before clarification, and using various methods of clarification. Table I-Analysis of Molasses P l u s Invert Sugar (Various methods used in preparation of sample) MOLASSES
DRYSUB-
INVERT-
STANCE SUGAR HEATED WITH C O N T E N T O F
FEHLING'S MOLASSES SOLN.
Grams
Per cenl
TOTAL
INVERT
CALCD. INVERTSUGAR CONMOLASSES TENT O F MIx TuR E SUGAR ADDEDTO
Per cent
Per cent
INVERT ~~~~~
Per cent
BEFORE CLARIFICATION
5.0 5.0
0.98 0.98
1.00 1.64
1.98 2.62
1.98 2.74
CLARIFIED WITH NEUTRAL LEAD ACETATE AND SODIUM CARBONATE
5.0 5.0 2.5
0.86 0.86 0.78
0.52 1.44
1.38 2.30
1.38 2.30
CLARIFIED WITH NBUTRAL LEAD ACETATE AND PHOSPHATE-OXALATE
5.0 2.5 2.5
0.84 0.68 0.68
1.98 0.93 1.76
2.82 1.61 2.44
2.84 1.62 2.47
The agreement between the found and calculated invertsugar contents is very satisfactory in all cases except one (5.0 grams molasses and no clarification), and since there is no evidence that any method used actually produces a lowering of the true invert-sugar content, the one showing the lowest amount in the original sample has been adopted. Cook and
McAllep,
Facts About Sugar, 23, 298 (1928).
283
Invert-Sugar Content as a Measure of Amount of Previous Inversion
The prime object of the investigation was to determine the rates of inversion of sucrose in beet sirups under conditions approximating those existing in the factory. If the copper reduction method is to be used for determining the amount of inversion, it is necessary to know whether or not invert sugar is being destroyed a t the same time that it is being formed. If such is the case, then the copper reduction method gives only the amount of invert sugar remaining in the solution and is not a measure of the amount of sucrose destroyed. In cases where molasses (60 per cent purity sirup) a t 50 per cent dry substance was heated a t 7 to 9 pH and 72' C., the invert-sugar content, as shown by copper-reducing power, decreased, showing that under these conditions the rate of destruction of invert sugar is greater than the rate of inversion. The results are given in Tables I1 and 111. of Invert Sugar in Mixtures of Molasses a n d Invert Sugar (Heated 1. 2, and 3 days at 72' C.)
Table 11-Loss
1 DAY
pH
Invert
1
Drop in
I
;:: 3i::;. 7 3 ;7:;. 2 0:?.;2 5 7;:;. 0 7.6 ORIGINALSIRUP
PH
Invert
Per cenl 1.56 2.27 1.56 2.27 1.56 2.27 ~~
7.4 7.4 8.0 8.0 9.0 9.0
i
3 DAYS
2 DAYS
Drop in
0.12 0.32 0.49
SIRUPAFTER HEATING Invert pH 7.1
7.4 8.2
Per cenl 1.48 2.14 1.51 2.14 1.47 2.14
1
pH
Drop in
7.0 6.9 6.9
0.16 0.35 0.53
Loss
I N INVERT
SUGAR
Per cent 0.08 0.13 0.05 0.13 0.09 0.13
These results show that the rate of decrease of invert depends on the invert-sugar content of the sirup, and that between the range of 7 and 9 pH the H-ion concentration appears to play a minor part. It was then found that invert sugar disappeared a t 6.0 pH a t about the same rate as a t the higher pH. The most important factors in determining the rate of destruction of invert sugar were found to be the purity and concentration of the sirups. As the concentration increased and as the purity decreased, the rate of destruction of invert sugar increased. Since factory sirups are, for the most part, held in a state of high concentration, the purity of the sirup is the determining factor in the rate of destruction of invert sugar under factory conditions. From this fact, apparently, arises the impression, held more or less generally among practical sugar men, that low-purity products may be held a t lower pH than those of high purity, without fear of loss through inversion. If the invert-sugar content of a sirup is taken as a mdasure of inversion, the inversion of a 90 per cent purity sirup starts well above 7 p H while it starts well below 7 pH in one of 60 per cent purity. In a 90 per cent purity sirup the invert-sugar content measures the inversion of sucrose fairly closely. In a 60 per cent purity sirup the pH must be lowered to some point under 7 before the rate of inversion exceeds the rate of destruction of invert sugar and an increase in invert
INDUSTRIAL A N D ENGINEERING CHEMISTRY
284
sugar appears in the sirup. Table IV shows the relation between, actual loss of sucrose and the increase in invert sugar present in sirups heated a t 80" C., at 80 per cent dry substance and a t various pH's. Table IV-Relation between Loss in Sucrose and Invert- Sugar Content of Sirups Heated a t 80 Per Cent Dry Substance at 80' C. (Loss in terms of per cent of original sucrose present lost per 24 hours)
I PURITY OF
1
I--
SIRUP
.I Per cent 90 75 60
~ P H
7 PH
I
8 PH
SUCROSE DESTROYED invertsugar content
Per cent Pep. cent 1.77 1.57 1.84 1.44 1.20 0.80
Actual
1
invertsugar By content
Per cent Per cent 0.50 0.60 0.46 0.32 0.37 Minus
1
BY
Actual
invertsugar content
Per cent 0.15 0.00 0.13
Per cent 0.14 Minus Minus
I
The sirups were prepared from a sample of molasses that contained invert sugar. Therefore inversion by invert-sugar content was measured by increase in invert-sugar content, and in the cases where destruction of invert sugar was more rapid than its formation the table shows negative results. The conclusion to be drawn from these results, and from numerous similar ones, is that, while the invert-sugar content of a high-purity sirup may be taken as a measure of inversion of sucrose, the invert-sugar content of low-purity products is of little or no value in calculating loss of sucrose.
Vol. 21, No. 3
by the same sirups after dilution to a point where the reading can be made. Purity and temperature are probably important factors in affecting the relation between the observed pH of a sirup and its actual pH as it exists in the pan, storage tanks, etc. Therefore, it is not surprising that the present investigation failed to show the inversion rate proportional to the H-ion concentration of the sirup. A glance a t Table IV shows that the actual rate of loss of sucrose increases between three to four times with a drop of one point in pH. In this connection it should be stated that the pH of the sirups did not always remain constant throughout the heating period. Samples a t 6 pH remained constant, samples a t 7 pH would drop as low as 6.2, and those a t 8 pH dropped as low as 7.5. At intervals throughout the heating period the samples were analyzed for pH and the pH was adjusted to 0.1 above the recorded point. Attempts to make the pH constant through addition of buffers only made the drops more rapid. Table V shows variations in pH observed and gives some idea of the average pH a t which the sirups were heated. Table V-pH
I
PURITY OF
SIRUP
Variations in Sirups Heated a t SOo C.
1
I
MAX. MIX. FINAL MAX. MIN. FINAL MAX. MIN. FINAL
Per cent
90 75 60
1 66.0 .0 6.0
6.0 6 .0 6.0
66..00 1 ; :7.1 ;
6.0
6.2 6.6 6.6
6.6 1 88.1 6.4 .1 6.6 8.1
7.5 7.8 7.8
7.5 8.1 8.1
Effect of Various Factors on Inversion Rates
At the outset it should be stated that the absolute accuracy of the results to be given is questionable, since numerous difficulties were encountered and the limited time available did not permit the working out of refinements required for accuracy. Chief among the difficulties encountered was that in measuring and controlling the pH of sirups. This is especially unfortunate, since pH is the factor of highest importance in the investigation. The pH of the solutions was adjusted by means of acetic acid or sodium hydroxide, and was measured colorimetrically on the cold dilute solution. Inversion was determined by loss in sucrose, sucrose being determined by enzyme hydrolysis. Obviously, pH should be determined on the sirup a t the concentration and temperature a t which inversion is measured. This is not feasible by any method known to the authors. Electrometric measurements of H-ion concentration by means of the hydrogen electrode or the quinhydrone electrode proved unsatisfactory. The hydrogen electrode was poisoned with extreme rapidity. At pH's above 6 the quinhydrone electrode gave results which were known to be too high. Below pH 6 the quinhydrone electrode gave results showing good agreement with the colorimetric method, but since this is out of the range normally encountered in factory practice, little use was made of the quinhydrone method. The colorimetric method was therefore adopted, in spite of its lack of sensitivity and the further objection of the necessity to dilute highly colored solutions. Regarding the effect of dilution on the pH measurement nothing conclusive was obtained. Concentrated solutions made from pure sucrose and phosphate buffer showed decided change in pH on dilution, though the pure buffer solution showed no appreciable change over the same range in concentration of buffer salt. A factory sirup of about 75 per cent purity, carbon-filtered to decolorize sufficiently to enable making colorimetric reading a t 70 per cent dry substance, showed practically no change in pH when read over the range of 10 to 70 per cent dry substance. It appears certain that in highly concentrated sirups the pH must be different, by an unknown amount, from that shown
It is seen that the control a t 6.0 pH on all sirups, and a t 8 pH on 75 and 60 per cent purity sirups, was perfectly satisfactory, and at 90 per cent purity and 8 pH no serious error entered. The interpretation of results a t 7.0 pH is uncertain. Owing to the variations in pH which occurred while the sirups were being heated, the statement that a drop of one point in pH increased the inversion rate three to four times is not strictly correct. Spengler and Todt6have calculated the rate of inversion of sucrose a t various H-ion concentrations and temperatures, basing their calculations on the inversion constant for sucrose in hydrochloric acid given by Jackson and Gillis, and assuming the inversion rate to be proportional to the measured H-ion concentration. These investigators note that their calculated rate is higher than that observed by Saillard6 in low-grade products, and offer as an explanation the possibility that the differencein H-ion concentration in the cold solutions, in which the pH was measured, and in sirups heated to the temperature a t which the inversion was allowed to proceed, may account for the discrepancy. Saillard's article is not available to the authors, but if he has measured inversion rate in the usual manner-that is, by invert-sugar content of the treated sirup-the observed rate of inversion would be lower than the Spengler and Todt calculated rate, owing to destruction of invert sugar in the lowpurity products. It is noteworthy that in the case of raw sugar (high-purity product) the calculated and observed rates checked much more closely. The actual rate of loss of sucrose observed in the present investigation, in the range of 6 to 8 pH, is somewhat higher than that calculated by Spengler and Todt. By extrapolation Spengler and Todt's curves show about 0.8 to 0.9 per cent of the sugar present inverted a t 80" C. and 6 pH in 24 hours. I n the present investigation the rate, calculated from loss in sucrose, was found to be between 1.4 and 2.0 per cent, under corresponding conditions, on products of 75 to 100 per cent purity. At 7 and 8 pH the observed rate is about six Spengler and Tddt, Z . Ver. d e r f . Zucker-Ind., 78, 393 (1928). Circ. 1996, 1888, 2000 (1927),Suppl. rose. 8
e Saillard, Hebdom Cornit6 Centr. Fabr. Sucre France,
I N D U S T R I A L A N D ENGINEERIXG CHEMISTRY
March, 1929
PH
OF
SOLUTION
PURITY O F SIRUP
Start
Finish
Per cent 100 100 90 90 75 75 60 60
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 5.95 6.0 6.0 6.05 6.0 6.1 6.0
SUCROSEPRESENTINVERTEDPER 24 HOURS
Per cent 2.05 1.85 1.45 1.8 1.4 1.8 1.1 1.2
The decrease in rate of inversion with decreasing purity is marked. At 7 and 8 pH the same trend was indicated, though difficulties in controlling pH made the results uncertain. Observations as to the effect of temperature on the inversion rate agreed with those of previous investigators, the rate increasing from two to three times with a rise of 10' C. in temperature. Sugar solutions of 90 per cent purity heated 80" C. and 6 pH showed about 1.6 per cent sugar present inverted per 24 hours; a t 105" C. and 6 pH the rate was from 10 to 12 per cent. This is equivalent to an increase of about 2.2 times per 10" C. increase in temperature. The effect of concentration of solution on the inversion rate was found to be negligible over a wide range, as shown in Table VII. Table VII-Effect
OF SoLUT1oN
Per cent 100 90 90 90
of C o n c e n t r a t i o n on R a t e of Inversion of Sucrose (Solutions heated a t 80' C. and 6 . 0 pH)
SUBSTANCE IN SOLUTION DRY
-I
p e r cent
1
PH OF SOLUTION Start
Finish
I 6.0
10
I
I 6.0
6.1 5.9
SUCROSE LOSTPER 24 HOURS
Per cent 1 . 9 5 (av.) 1 . 6 (av.) 1.7 1.5
I n view of the wide range in ratios of sugar, water, and impurities existing in the various solutions handled, such relative constancy in inversion rates is somewhat surprising, and i t appears that results obtained when examining sugar solutions of comparatively low concentration may be applied, with fair accuracy, t o the concentrated sirups actually handled in factory practice.
285
The h a 1 factor investigated was the effect of the type of impurities present on inversion rate a t a given pH. Three sirups of the same purity, but obtained from different sources, showed the same inversion rate a t 6 pH and 80" C.-that is, about 1.6 per cent of the sucrose inverted per 24 hours. A fourth sirup, abnormal in nature, varied greatly in pH during heating, but the results indicated that had the pH been controlled the inversion rate would have checked that obtained on the other three. The pure sugar sirups (Table VI) inverted a t 6.0 pH and 80" C. cptained 1 per cent phosphate buffer on solution and showed only slightly higher inversion rate than the F O per cent purity factory sirups. Somewhat different results were observed on solutions of sugar, water, and inverting agent alone, a t low pH. Sixty per cent sirups were made from a number of commercial refined sugars; to each of these sirups 0.12 per cent tartaric acid on sucrose was added, and the acid solutions were heated for 30 minutes a t 80" C. The amount of invert sugar formed was then determined. A second series of tests was made, duplicating the first except that 0.7 per cent sodium chloride on sugar was added to the solution. Table VI11 shows the results obtained on three different sugars, selected because the pH of their solutions remained constant before and after heating. pH was determined by the quinhydrone electrode method. Table VIII-Inversion of Sucrose b y Tartaric Acid (60 per cent sucrose solution heated with 0.12 per cent tartaric a d d at 80' C. for 30 minutes)
1 2 3
0.7y0 NaCl O N SKICROSS PRESENT
No NaCl PRESENT
SUGAR SAMPLE
pH
1
2.54 2.57 2.36
Invert sugar formed
Per cent 13.5 17.3 26.1
I
pH
2.50 2.50 2.37
Invert sugar formed
Per ccnl 22.4 26.2 37.5 ~
~~~
In all cases the acldition of sodium chloride greatly increased the inversion rate without markedly changing the measured H-ion concentration. Sixty per cent solutions of these same sugars were inverted in a similar manner, using standard citrate buffer, in place of the tartaric acid, to produce 3.0 pH. All showed about 18 per cent invert sugar formed in 30 minutes' heating a t 80' C. It is obvious that the inversion rate is not necessarily proportional to the H-ion concentration as determined on the cold solutions, and it is easy to conclude that the nature of the inverting agent used is responsible for the observed discrepancy. However, the authors believe that the discrepancies can be explained more logically by assuming that the change in H-ion concentration, resulting from raising the temperature of the solution from that at which the pH is measured to that a t which the inversion rate is determined, may vary decidedly with the nature of the inverting agent employed. It seems probable that in sugar-beet sirups the type of impurities remains nearly enough constant and the solutions are sufficiently well buffered so that relatively constant inversion rates may be expected.
New Books Coal5elds of Scotland. The Carbonisation of "Kinneil Gas" Coal. Physical and Chemical Survey of the National Coal Resources No. 11. Department of Scientific and Industrial Research. 35 pp. H . M. Stationery O 5 c e , London. Price 1 s. 6 d. ner. Fundamentals of Chemical Thermodynamics. Part I-Elementary Theory and Applications. J. A. V. BUTLER. 207 pp. The Macmillan Co., New York. Price, $2.00, Gasfernversorgung Westsachsens, 1928. L. LITINSKY. 31 PP. Kreishauptmannschaft Leipzig, Landesplanung Westsachsen, Germany. Price, 1.50 marks.
Proceedings of the 7th Annual Meeting of the Highway Research Board. Held at Washington, D. C., December 1-2, 1927. ROY W. CRUY, Editor. Part I. Reports of Research Committees and of Special Investigations and Papers. 318 pp. Division of Engineering and Industrial Research, National Research Council, Washington, D . C. Price, $2.00. Reference Book of Inorganic Chemistry. WENDELL M. LATIMER AND JOEL H. HILDEBRAND. 442 pp. The Macmillan Co., New York. Price, $3.75.
