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I N D U S T R I A L A N D E N G I N E E R I N G C II E hl I S T R Y
zero-oxygen water, it, is necessary to treat the softened water with an oxygen-absorbing chemical. Because of the deaeration of the water by the temperature rise, much smaller amounts of chemical are needed to remove the remaining oxygen. Applebaum (a) has described a hot-process plant of 2,500,000 gallons per day capacity in which ferrous sulfate is used to remove the remainder of the dissolved oxygen. The equations show that this chemical is less efficient than sodium sulfite for the purpose:
++ +
2Na2SOs O2+2NazS04 4FeSOa O2 8NaOH 2Hz0 + 4Fe(OH)3
+
BOILER PRESSURES Lb./aq. in.
NazS206 HzO+2NaHS03 (3) 2NaHSOa 2NaHCOa --it 2NazSOs 2H20 2cOz ( 4 4 2NaHS03 Na2C03-+ 2?u’azSO8 HzO cO2 (4B) 2Na2S03 Oz +2NazS04 (1)
++ + +
It must be stressed that very close chemical control is necessary when the bisulfite is used, for an excess of the bisulfite will rapidly change the water to an acid condition as shown by Equation 3. The use of bisulfite would also be limited to a preheater, as the release of carbon dioxide (Equal ions 4 8 and 4B) in the boiler would be undesirable. Sodium sulfite does not possess these disadvantages, since the simple reaction (Equation 1) with oxygen occurs without changing the alkalinity of the water. The objection to the increase of soluble salts in the feed
PARTSNazSO4 PER PARTTOTAL ALKALINITY EXPRESSED ~8 NalCOs 1
Up t o 150 150-250
2 3
Greater than 250
A certain amount of alkalinity is carried in the boiler to prevent calcium sulfate scale and retard corrosion. Thus there is always a certain soluble salt content in the feed water, and the
(2)
Thus, the use of ferrous sulfate removes alkali from the m-ater, necessitating the addition of caustic soda or more lime in the water treatment. Careful control is necessary to prevent the water from becoming acid. However, if the water is too alkaline, or too high in bicarbonate, as in the plant Applebaum describes, then the use of ferrous sulfate will be equivalent to the addition of acid t o remove the excess alkali or bicarbonate. The presence of the precipitate of the ferric hydroxide may or may not be desirable, depending upon other factors. I n cases where very alkaline water or water high in bicarbonates must be treated with acid, or an acid salt, crystalline sodium metabisulfite (Xa2SzO5) may be used. This would undergo the following series of reactions when added to the feed water:
++ + +
water is valid only under certain conditions. I n order to prevent caustic embrittlement, the A. s. M. E. Boiler Code Committee (1)recommends that there be maintained in the boiler a certain ratio of sodium sulfate to total alkalinity. This ratio increases with the boiler pressure as follows:
(1)
+ 4Na~S04
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addition of sodium sulfate is usually beneficial. ACKNOWLEDGMENT The miters wish to thank W. L. Beuschlein for his practical suggestions during the course of this work.
LITERATURE CITED
.
(1) Am. SOC.hlech. Engr. Boiler Code Comm., Boiler Construction Codes, Combined Ed., pp. 402-3 (1931). (2) Applebaum, S. B., Mech. Eng., 56, 273, 341 (1934). (3) Backstrom, H. L. J., Trans. Faraday Soc., 24, 601 (1938). (4) Backstrom, H . L. J., 2.phys. Chem., B25, 122 (1934). (5) Crist, R H., J . Chem. Education, 8, 504 (1931). (6) Fager, E. P., and Reynolds, A. H., IND.ENG.CHEM.,21, 357 (1929). (7) Griffin, R. C., “Methods of Technical Analysis,” p. 703, New York, McGraw-Hill Book Co., 1927. (8) Moberg, A. R., Combustion, 3 (a), 36 (1931). (9) Powell, S. T., “Boiler Feed Water Purification,” Chap. VIII, N e w York, McGraw-Hill Book Co., 1927. (10) Reinders, TV., and Vles, S. I., Rec. trav. chim., 44, 249 (1925). (11) Semenoff, N., Chem. Rev., 6, 347 (1929). i (12) Solberg, T. W., Holmes, J. A., Summers, R. E., and Baker, L. R., i Power, 75, 70 (1932). (13) Speller, F. N.,J . Franklin Inst., 193, 515 (1922). (14) Titoff, .4.,2. phys. Chem., 45, 641 (1903). (15) Volkovich, S. I., and Belopolskii, A. P., J. Applied Chem. (E. S. S. R.), 5, 509 (1932). RECEIVED October 16, 1934. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14, 1934.
Hygroscopicity of Sugars and Sugar Mixtures JOHNH. DITTMAR, Arbuckle Brothers, Brooklyn, N.Y A definite relatiomhip between the sucrose, to increase the t e n d e n c y to invertsugar, and water content of various sugars absorb moisture, and probably desirable to know a t just to be due to the fructose in the what r e l a t i v e humidity and the relative humidity of the surrounding atinvert sugar. H o w e v e r , no a sugar or sugar mixture must b e m a i n t a i n e d so t h a t i t s mowhere has been found, and the equilibrium definite relationship was estabwater content will remain conpoints have been graphed. T h e equilibrium lished between the amount of relative hum,idity or vapor pressure of pure SUinvert s u g a r i n t h e s u c r o s e stant, or below what point the erose, dextrose, fructose, invertSugar, or sucroseproduct, the amount of water alrelative humidity must be held ready present, and the relative in order to overcome the hygroinvert sugar mixtures with rarying percentages of humidity. Browne in 1922 scopic tendencies of the sugar. This is especially truefor invert water can be determined directly f r o m the graph. measured the moisture absorption of various sugars a t 60 and sugar and f r u c t o s e (levulose) which begin to absorb water a t comparatively low relative 100 per cent relative humidity during various periods of time. humidities. The importance of maintaining a controlled No relationship was established for any other relative humidity, amount of moisture in sugars is especially to be stressed in nor were mixtures considered. I n 1930 Whittier and Gould relation to bacterial growth, inversion, fermentation, and (8) measured the vapor pressure of sucrose, glucose, and gahardening or softening of sugars and sugar mixtures in stor- lactose a t 25” C. in saturated solution and used these figures age, and in the general troubles experienced with hygroscopic as a measure of their tendencies to absorb moisture; they argued that the hygroscopic tendencies of solids are, for pracsugars. The presence of invert sugar in a sucrose product was known tical purposes, those of their saturated solutions. These
F
OR many purposes it is
’
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I N D U STR I A L A N D E N G I N E E R I N G CH E MI S T R Y
Vol. 21, No. 3
would begin was much lower than the actual point for invert free sucrose. Since commercially pure granulated sugars usually contain amounts of invert sugar from 0.05 to 0.2 per cent, i t is well to bear this point in mind in using the graphs. OBSERV.4TIONS
One of the interesting points observed in making the experiments was the sharp point a t which liquefaction of all the crystalline sugars took place. There was no exception found in the fact that the crystals seemed to be able to hold water in surface solution until 15 per cent water had I been absorbed, at which point some crystals in I themass passed abruptly into solution. If the a percentage relative humidity was lowered before this point had been reached, the sugars would return to dryness without any change except for hardening due to the cementing together of the crystals. PERCENT WATER IN EQUILIBRIUM AT Z S ' C , Another point observed was the difference in absorption between crystalline invert sugar and FIGURE 1. PERCENTAGE WATERIN SUGARS IN EQUILIBRIUM AT VARIOUS RELATIVE HUMIDITIES f r u c t o s e , and plastic or noncrystalline invert s u g a r a n d fructose. The plastic form was were the only data available in the literature on the hygro- . obtained by gently melting dry pure fructose and a 50-50 scopicity mixture of dextrose and fructose. The resulting plastic form . of sugars. did not recrystallize throughout the experiment and showed MEASUREMENT OF EQUILIBRIUM POINTS the recorded difference in absorption from the crvstalline I n making hygroscopic measurements of this type, the sugar. Figure 1 shows how the lines for the crystaiine and simplest arid most convenient apparatus is the familiar sul- plastic forms of fructose met at 20 per cent water absorption. furic acid chamber, containing known concentration of acid An attempt was made to plot a line for plastic dextrose, but in a large desiccator or other sealed enclosure, which gives an the dextrose partly recrystallized during the progress of the atmosphere of definite relative humidity calculated from the experiment, which required a few days for each equilibrium vapor pressure of the sulfuric acid. This method appears to point observed. However, during the attempt i t was noticed be superior to other methods-e. g., the isothenoscopic meas- that the plastic dextrose started to absorb at about 32 per urements of the vapor pressurebecause the atmospheric conditions produced artificially in the humidity chamber closely simulate the conditions which the sugars and sugar products encounter in actual commercial use in warehouses, etc. BP One gram of the sirup or sugar crystals 3 (bone-dry) whose absorption curve was to be s measured, was spread over a tared watch glass 3P and placed in a humidity chamber whose relative humidity was below the point at which 4 the sugar or sirup would begin to absorb water. E4 5o Then in increments of 2 to 3 per cent relative 5 humidity it was placed in successive chamI bers and allowed to remain in each until sucP TI 0 cessive weighings showed that equilibrium had 8 been reached. The temperature was kept as rn close to 25"C. as possible, and weighings were n o t m a d e u n t i l the temperature had not varied more than +2.0° C. for 5 to 6 hours previously. The increase in weight measured the amount Of absorption and, therefore, the FIGURE 2. EQUILIBRIUM C W R T FOR SUCROSE-INVERT SUGAR MIXTURES amount of water in equilibrium at this relative AT 25' c. humidity; from this figure the vapor pressure of the mixture could be calculated. The results were checked cent relative humidity, the absorption being not over 1 per by taking sugars of known sucrose, invert sugar, and water cent until 60 per cent relative humidity had been reached, content (soft or brown sugars) and placing a weighed amount when absorption became very rapid. The line is not included in a humidity chamber whose percentage relative humidity in Figure 1 because of the partial crystallization observed. Extrapolation of the curves (Figure 2) for the sucrosewas shown by the graph to be in equilibrium with a sugar of that analysis, and the sugar was found neither to gain nor invert sugar mixtures indicates that, when the invert sugar in lose moisture. I n the case of dextrose and levulose the c. P. sucrose reaches about 20 per cent, the mixture will absorb product sold under U. S. P. regulations was used. I n the like pure invert sugar or fructose. It also proves that the case of sucrose it was found that, if as little as 0.1 to 0.2 per invert sugar in soft (brown) sugars is in a noncrystalline state cent invert sugar was present, the point at which absorption -i. e., in a plastic condition.
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March, 1935
INDTJSTRIAL AND E N G I N E E R I N G CHEMISTRY PRACTICAL VALUE O F THE
GRAPH
From the many articles on the storage of raw sugar in humidity-controlled warehouses to prevent bacterial growth by maintaining the factor of safety, and consequent inversion a n d deterioration, the practical value of this type of graph can readily be seen. I t may also be used for soft (brown) sugars, granulated sugars, and products of high sugar content. T h e graph may be within practical limits for honie3, candies, chocolates of high sugar content, corn sugar (glucose) products, etc. Those attempting to prepare levulose in crystalline form for commercial use mill do well to give particular attention to the rather low percentage relative humidity a t which this Droduct absorbs water. There is n o doubt but that this type of graph is not the
335
last word on the absorptive properties of sugar. There are many factors in this problem that are not yet known or understood; it is hoped that this article will stimulate further work to obtain definite information. (1) (2) (3) (4)
BIBLIOGRAPHY Browne, C. A,, J. IXD. EXG.CHEM.,14, 712 (1922). Edgar and Swan, J . Am. Chem. Soc., 44, 570 (1922). Honig, R., Intern. Sugar J., 31, 214 (1929). King, R. H., and Suerte, D., Ibid., 32, 542 (1930).
(5) Owen, W. L., Ibid.,24, 581 (1922). ( 6 ) Sandra, K., Listy Cukrovar., 51, 314-18 (1933). (7) Smith and Menaies, J. Am. Chern. Soc., 32, 1412 (1910). (8) Whittier, E. O., and Gould, S. P., IND. ENQ.CHEM., 22, 78 (1930).
RECEIVED November 15, 1934.
Peroxidase in the Darkening of Apples A. K. BALLS AND W. S . HALE,Bureau of Chemistry and Soils, Washington, D. C.
A
that the tissue, nhen f e hlY LTHOUGH other reactions Darkening of the freshly cut surfaces of apples cut, darkened more rapidly and are necessary preliminais a reaction that is catalyzed by peroxidase. c o n s i s t e n t l y than that of the ries to the formation of The formation of hydrogen peroxide by a respiraother common varieties availt h e brown pigment 011 the surtion enzyme which uses molecular oxygen is a able.) face of freshly cut apple tissue, necessary preliminary step. Both the fruit tissue the steps which culminate diDECOMPOSITION OF PEROXIDH rectly in the production of pigand the juice darken in the absence of air, but BY CATALASE m e n t are accelerated by peronly until the peroxide present is complelely Ten grams of peeled apple tiso x i d a s e . A theory of tissue utilized. The reaction continues on further sue were ground in a mortar with oxidation which involves per100 grams of ice, the pul was addition of peroxide or on reexposure to air, oxidase was long ago proposed filtered rapidly, and the &trate when peroxide is again produced enzymically. was kept in an ice bath during the by Bach and his co-workers (2) experiment. From 20 cc. of this a n d was used by Onslow in exPigment formation is accelerated by horse-radish diluted juice, 2-cc. portions were plaining the darkening of fruits peroxidase. I n boiled apple pulp the addition of removed at intervals and mixed (4). It seems to fit the facts with one drop of a 1.5 per cent both peroxide and peroxidase is required. observed on apples very well, alcoholic solution of guaiacum. The inhibition of peroxidase is therefore of A positive reaction, the rapid as long as pigment formation is formation of an intense blue color, importance in delaying the discoloration of cut regarded as subsequent to a procwas observed undiminished in the ess of direct oxidation such as fruit. Peroxidase inhibitors fall into two classes: untreated juice for 15 minutes. t h a t regulated by the respiraAfter 25 minutes the color was substances that affect ihe enzyme directly and subappreciably weaker than a t the tion ferments. It is unnecessary stances that accelerate its inactivation by hydrogen beginning. The apple peroxidase t o discuss here whether or not itself had, therefore, no rapid effect peroxide. The former class, which includes the such a Fystem corresponds to at this temperature on the perthe o x y g e n a s e s of Bach and sulfhydryl compounds, is more important f o r the oxide present. To 20 cc. of the same diluted C h o d a t . In addition t o t h e inhibition of fruit darkening. Treatment of juice, 0.25 cc. of catalase solution evidence to be found in earlier sliced apples with a dilute solution of glutathione was added [l.O gram of Hennich' work, the behavior oi' apple tiscrude liver catalase (3) was susor cysteine salts permils drying or long-continued sue and apple juice observed in pended in 100 cc. of water and the keeping wilhout discoloration. The su[Shydryl insoluble material was then rethe f o l l o w i n g e x p e r i m e n t s moved in the centrifuwj. One strongly supports this view. The dericaiiee occurring in pineapple juice as the minute after the introdurtion of d a t a given are typical of a much natural actitlator of bromelin has the same effect. the catalase (at 0" C.) the blue larger amount which it does not color was weak, and after 10 minutes it was absent. Hydrogen seem necessary to cite. Oxidation by peroxidase requires the presence of a per- peroxide in the proportion of 0.10 cc. of 0.1 N hydrogen peroxide to 10 cc. of juice was addpd 25 minutes after the catalase addioxide; the ferment cannot use molecular oxygen. Both per- tion. This caused a temporary recurrence of the reaction with oxide and peroxidase are known to be present in apple tissue. guaiacum tincture, which was again very strong at first but became negative after another 10 minutes. This reaction indicated The former mag be recognized by the usual potassium iodidestarch method,-and thepresence of both may be detected by that t h e peroxide, not the peroxidase, had varied during the the coloration of tincture. peroxide is also experiment. The addition of peroxidase to the juice had no effect at 0" C. except t o intensify the guaiacum reaction. found in the press juice and in the water extract of fresh The peroxide in apple tissue is therefore hydrogen peroxide, apples, where it may be decomposed by catalase. as shown in the following experiment with a water extract of Paragon or is capable of changing into hydrogen peroxide which is apples. (This variety and the almost identical Arkansas the only peroxide decompoeed by catalase. The presence of Black Twig variety were used in all the experiments reported hydrogen peroxide is to be expected, since Wieland and his here. They were chosen because preliminary tests showed co-workers (6) have shown by quantitative measurements
