1422
INDUSTRIAL AND ENGINEERING CHEMISTRY
D A = diffusivity for N204-carriergas system, sq. cm./sec. D, = diffusivity for NOQ-carrier gas system, sq. cm./sec. M , = molecular weight of liquid NOz N Q = absorption rate, gram moles NOa/(sec.)(sq. cm.), as indicated by gas analyses N L = absorption rate, gram moles NOz/(sec.)(sq. cm.) as indicated by liquor analyses PA = partial pressure Nz04 in main body of gas, atm. p~ = mean partial pressure of nondiffusing or carrier gas in gas film, atm. = partial pressure of NOz in main body of gas, atm. = total pressure, atm. R = gas constant, cc.-atm./(gram moles) (" K.) Re = Reynolds number = dcp/p T = absolute temperature, K. z = effective film thickness, om. X H Z O = effective film thickness for evaporation of water, em. XNZO = effective film thickness for absorption of NOn, em. y = thickness of stagnant gas layer in diffusivity experiments, cm. p = gas viscosity, gram/(sec.)(cm.) p = gas density, gram/(cc.) p~ = liquid density, grams/(cc.) 8 = time, sec.
B
Literature Cited (1) Abel, E., Sohmid, H., and Stein, M., 2. Elektrochem., 36, 692 (1930). (2) Bodenstein, M., Ibid., 24, 183 (1918).
VOL. 29, NO. 12
(3) Bodenstein, M., Ibzd., 22, 327 (1916); 2. physilc. Chem., 100, 68 (1922). (4) Bolshakoff, P. E., 5. M. thesis, Mass. Inst. Tech., 1934. (5) Briner, E., S.chim. phys., 23,848 (1926). (6) Burdiok, C. L., S. Am. Chem. SOC.,44, 244 (1922). (7) Burdick, C. L.,and Freed, E. S., Ibid., 43, 518 (1921). (8) Chambers, F. S., and Sherwood, T. K., Ibid., 59, 316 (1937). (9) Chilton, T. H., Duffey, H. R., and Vernon, H. C., IND. ENO. C H E M .29, , 298 (1937). (10) Foerster, F., and Koch, M., 2. angew. Chem., 21,2161 (1908). (11) Frantz, M., 2.physilc. Chem., 47,513 (1904). (12) Gilliland, E. R., IND.ENQ.C H ~ M 26, . , 681 (1934). (13) Gilliland, E. R., and Sherwood, T. K., Ibid,, 26, 516 (1934). (14) Hasohe, R. L., S. Am. Chem. SOC.,48, 2253 (1926). (15) Koehler, A., and Marquerol, M., Bull. SOC. chim., 13, 69 (1913). (16) Natanson, E. L., Wied. Ann., 27, 606 (1886). (17) Partington, J. R., and Parker, L. Y., S. SOC.Chem. Ind., 38, 75 (1919); 43,52T (1924). (18) Roberts, J. B., S. M. thesis, Mass. Inst. Tech., 1936. (19) Russ, F., 2. physik. Chem., 82, 217 (1913). (20) Sohreber, Ibid., 24, 651 (1897). (21) Sherwood, T. K., "Absorption and Extraction," New York, MoGraw-Hill Book Co., 1937. (22) Taylor, G. B., Chilton, T. H., and Handforth, 8. L.. IXD. ENQ. CHEM.,23, 860 (1931). (23) Verhoek, F. H., and Daniels, F., J. Am. Chem. SOC.,53, 1250 (1931). (24) Wourtzel, E., Compt. rend., 169, 1397 (1919). RECBIVED September 27, 1937. Presented before the meeting of the American Institute of Chemmal Engineers, St. Louis, Mo., November 17 t o 19, 1937.
Effect of Humidity on ygroscopic Properties of Sugars A. SOKOLOVSKY
Confectionery Scientific-Research Industry, Institute Moscow, U. of the S. S. R.
T
HE hygroscopicity has been investigated of saccharose, maltose, lactose, dextrose, levulose, galactose, and caramel made from saccharose and treacle with the addition of various sugars a t relative humidities of 43, 62.7, 81.8, and 88.8 per cent. The experiments were made a t 25" C. and lasted for 60-75 days. The temperature mas held constant in the thermostat a t 25" C. ( *O.lo). The sugar specimens were dried in vacuo until constant weight was obtained. Approximately I-gram specimens of these anhydrous substances were placed in a weighed vessel and transferred to a desiccator over a saturated salt solution which created a constant relative humidity in the vacuum of the desiccator. The moisture-absorbing capacity of the specimens was obtained by weighing the vessels containing them a t certain intervals, the difference in weight giving the amount of moisture absorbed. Specimens of caramel contained from 0.4 to 0.8 per cent moisture. The amount of moisture absorbed by the caramel under various conditions of relative humidity was found by the above method. The data relating to the equilibrium conditions of supersaturated salt solutions with air are taken from the work of Adams and MereV2 1 Browne [J. IND.ENQ.CHEW., 14, 712-14 (1922)l carried out experiments on various pure augars and commercial sugar products. Dittmar [raid., 27, 333 (1936) ] experimented with the hygroscopicity of certain sugars. 2 IND.ENQ.CHEM., 21, 305 (1929).
and Caramel' Bor the experiments the following saturated solutions were prepared: K2C03.2Hz0corresponding a t 25" C. to 43 per cent relative humidity, T\T&N03 corresponding to 62.7 per cent, (NH4)&04 corresponding to 81.8 per cent, and KzS04 corresponding to 98.8 per cent. The saturated solutions of these salts were placed a t the bottom of the desiccator and over them were placed the vessels containing the sugar samples to be investigated. The desiccator was covered with a close-fitting lid at all times, and a vacuum was thus created in which a constant relative humidity was maintained. When the sugar specimens were kept in the desiccator at a relative humidity of 62.7 per cent, the greatest absorbing capacity (9.93 per cent) was exhibited by maltose during the first 17 days. In the same period levulose absorbed 7.09 per cent of the moisture. The smallest quantity of moisture under the same conditions was absorbed by galactose, 0.03 per cent. After 76 days under the same conditions, the greatest quantity of moisture was absorbed by levulose, 21.4 per cent. After 17 days the amount of moisture absorbed by maltose showed little variation. The smallest quantity of moisture was absorbed by galactosk, 0.03 per cent. Levulose absorbed 15 per cent moisture, and then changed from the crystal to the liquid form. When the different specimens of sugar were kept in the desiccator at a relative humidity of 81.8 per cent, during the
DECEMBER, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
1423
TABLE I. MOISTURE ABSORPTIONAT VARIOUSRELATIVE HUMIDITIES (25" C.) l>ay
Sugar
0.06 4.61 0.03 0.04 0.65 0.05
Saccharose Maltose(anhydrous:b Lactose Dextrose LevuloseC Galactose
0.05 8.52 0.07 0.62 4.18 0.06
1 day Saccharosed Lactosea Dextrose{ Levulose0 Galactose
1.31 0.05 4.68 11.09 1.16
Per Cent Moisture Absorbed in: 3 days 7 days 17 days 30 days 50 days 60 days 62.7 Per Cent Relative Humidity 0.05 0.05 0.05 0.05 0.06 0.05 8.14 9.77 9.93 9.85 9.9 10.01 0.03 0.03 0.05 0.05 0.05 0.05 0.04 0.04 0.38 0.43 0.79 1.07 1.41 2.61 7.09 13.01 18.35 21.85 0.03 0.03 0.03 0.03 0.03 0.03 81.8 Per Cent Relative Huiniditv 0.05 0.05 0.05 2.28 4.54 3.86 9.2 9.8 9.96 10.77 , 0 . 0 7 0.07 0.07 0.11 0.11 0.11 2.04 5.15 9.7 9.62 9.77 9.6 10.22 18.58 29.16 35.05 36.32 35.3 0.06 0.06 0.07 0.13 0.16 0.06 98.8 Per Cent, Relative Humidity 3 days 7 davs 11 davs 20 days 26 days 40 days 4.85 13.63 20.81 33.01 38.53 45.62 0.09 0.12 0.13 0.26 0.05 0.33 8 . 6 1 15.02 20.78 28.43 33.95 42.82 18.43 30.74 37.61 45.95 49.41 54.99 1 . 5 4 3 33 6.18 8.34 10.47 16.42
..
...
first 24 hours the greatest quantity of moisture was absorbed by maltose, 8.52 per cent; within the same period levulose absorbed 4.18 per cent moisture. The smallest amount under the same conditions was absorbed by lactose, 0.07 per cent. After 76 days under the same conditions levulose absorbed the greatest percentage of moisture, 35.5; maltose absorbed the next largest amount, 10.77 per cent in 30 days, after which it became moldy and the experiment was stopped. Dextrose was third with 26 per cent moisture absorbed in 76 days and the smallest quantity was absorbed by lactose (0.07) and galactose (0.11 per cent). When the sugar samples were kept in the desiccator with a relative humidity of 98.8 per cent, they absorbed large quantities of moisture, with the exception of lactose. In 40 days levulose absorbed the greatest quantity, 54.99 per cent; saccharose absorbed 45.62, dextrose 42.82, galactose 16.42, and lactose only 0.38 per cent. On the first day maltose became moldy and was not weighed. After having absorbed 15-18 per cent moisture, levulose, saccharose, and dextrose began to liquefy. These experiments showed that, when the specimens were kept a certain length of time, the greatest hygroscopicity was exhibited by levulose and the least by lactose. After crystalline sugars absorbed 16-18 per cent moisture, they became liquids. Maltose absorbed a large quantity of moisture within the first few days, and became moldy at the same time.
I 2
1 2
3
4
6
6 7
3 days
5 days
11 days
0.15 0.29 0.25 0.21 0.33 0.32 0 25
0.28 0.35 0.31 0.32 0.34 0 36 0.32
0.34 0.46 0.41 0.40 0.41 0.45 0.36
0.56 0.65 0.56 0.67 0.56 0.72 0.52
0.83 0.69 0.73
2.29 0.94 1.79 1.73 1.27 1.53 1.43
2.35 2.09 2.03 1.92 1.39 1.6 1.45
2.65 2.52 2.67 2.2 1.73 2.06 1.74
10.87 8.16 7.81 7.24 5.92 7.09 4 64
15.32 11.76 12.12 9.22 8.57 10.11 6.97
0.06
0.66 0.61
o
0.05 9.95 0.08 1.74 21.4 0.03
All the levulose crystals liquefied. After 30 days mold began to form. After 6 days the levulose crystals began to liquefy; after 30 days a mobile liquid was formed, d The saccharose crystals began to decompose and liyuefy after having absorbed a proximately l6-18% of the moisture. when they had absorged, apprqximately 36-38% all t h l crystals turned into a mobile liquid; when up to 45% of the moisture had been absorbed a film of mold was formed a After the lactose had keen kept for 25 days a n d had absorbed an insignifioant amount of moisture, it was covered with mold. f When the dextrose had absorbed 15-18% of the moisture it began todissolve; when it,had absorbed 4 2 % , i t oompletel; liyuefied and was oovered with mold. # When the levulose had absorbed approximately 15% of the moisture, it began to dissolve. After having absorbed approximately 30%, it liquefied. a
C
3.9 0:07 9.6 35.5 0.11
60 days
...
...
59:i4 26.72
Caramel Test Absorption of moisture by caramel, made from saccharose with the addition of different sugars, was carried out a t relative humidities of 43, 62.7, and 81.8 per cent. Various kinds of caramel were prepared as follows: Compn. No. 1 2 3
Saccharose Grams 100 100
100 100 100 100 100
4
5 6 7
Treaole (Dry) Grams 4-40 f35
Other Ingredient Grams
i-30
i-35 i-37.5 i-36 f37.5
....
dextrose dextrose maltose ?. 5 levulose o dextrin 2 5 starch 5
10 5
The caramels were prepared in the laboratory at 135' C. in a 740-mm. vacuum. The initial humidit,y of all the samples was between 0.4 and 0.8 per cent. The air temperature was 25" C. The samples were placed in dried and weighed vessels, which were then reweighed and placed in a desiccator with a close-fitting lid. The quantity of absorbed moisture was determined by weighing the samples at different intervals. As shown in Table 11, caramel is highly hygroscopic and attracts moisture even at a low relative humidity. The hygroscopicity of caramel is higher than that of its different ingredients. The composition of the caramel has little effect upon its hygroscopicity. RBCIOIVED July 16. 1937.
TABLE11. MOISTURE ABSORPTIONBY CARAMEL AT VARIOUSRELATIVE HUMIDITIES (25' C.)
-
Caramel No. 1 day
3 4 5 6 7
76 days'
613
2.36 1.91 1.77 1.83 1.44 2 1 71
7.2 5.56 5.04 4.97 3.83 4.81 3 59
Per Cent Moisture Absorbed in: 20 days 26 days 32 days 40 days Relative Humidity, 43 Per Cent 0.66 0.81 0.87 0.9 0.75 0.93 1.01 0.88 0.76 0.78 0.63 0.74 0.99 0.91 0.84 1.07 0.66 0.73 0.7 0.81 0.84 1.13 1.08 6.64 0.73 0.61 0.69 Relative Humidity, 62.7 Per Cent 3.28 3.58 3.61 4.1 4.04 4 69 4.64 ._. 4.52 5.31 ... ... 2.83 3.17 3.1 3.58 3.28 3 73 3.37 3.67 2.91 3.22 3.28 3.83 2.42 2.73 2.79 3.81 Relative Humidity, 81.8 Per Cent 18.45 19.18 21.64 16.01 16.16 18:46 18.21 15.97 17 04 20.27 19.99 12.29 13.89 14.34 16.65 11.33 12.34 14.6 14.59 13.25 15.3 17.79 17.84 8.85 11 15 12 81 13.52
50 days
60 days
1.06 1.13 0.85 1.37 0.92 1.41 0.82
1.18 1.14 0.86 1.4 0.97 1.41 0.82
3.9 4.85 5.67 3.48 3.78 3.63 3.42
4.15 5 5 .?3 3.61 3.92 3.92 3.47
21.93 20.79 19.89 16.62 15 18.77 15.68
21.81 21.08 18.32 15.05 19.23 15 62
22.61
75 days 1.2 1.18 0.96 1.4
0.9s
1.48 0.88
4.82 5.88 6.39 4.3 4.6 4.46 3.93
.. .. .. .... ..
..
Start of Crystallization Days 20 26 (grew cloudy in 11 days) 3 20 3 3 3 3 3 3 3 3
(started t o liquefy in 5 days) (started to liquefy in 3 days also) (started toliquefy in 7 days) (startedtoliquefyinlldays) 5 (started to grow cloudy in 3 days) 3
All the specimens began to crystallize in 8 to 12 hours: in 40 to 50 hours they began to liquefy. in 40 days they began to be coverkd with mold.
