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INDUSTRIAL AND ENGINEERING CHEMISTRY
From the trend of the data on salt effect by Myers and Baker ( 5 ) , it may be assumed that a t p H values below 3.35 the addition of a slight amount of salt will bring about a decrease in strength of jellies. The lower the p H the more rapid will be this decrease for a like amount of salt. I n the comparison of the strength of jellies made u p a t the same p H from the first and second extractions from the cranberries, it may be said that the total cation Concentration is higher in the first extraction, and that coagulation and precipitation or pregelation tendencies are greater. Therefore, the strength of the jelly would be lower. According to Spencer (11) a sodium salt decreases the jelly field on the acid side. It may be assumed that the jelly strength would be similarly affected by the potassium salt. It is well known that potassium acid tartrate has this effect on the formation of jelly from juice extracted from overripe grapes. The differences in jelly strength between the jellies from the lemon and the cranberry pectins may be partly due to the differences in actual pectin present. A determination showed 75.76 and 69.28 per cent pectic acid present in the 0.5 per cent solutions of the lemon and cranberry pectins, respectively. This difference in pectic acid is not considered as important in jelly formation as the degree of polymerization of the galacturonic acid ( 7 ) . The relative concentrations of basic ions (calcium, magnesium, potassium, sodium) in the pectin from the lemon and
375
the cranberry may account for part of the variations in jelly strength of jellies from the two sources. This phase was not within the scope of the investigation. Consequently, analysis of the pectin ash which would bring out these relationships was not made.
Acknowledgment The p H measurements were made by G. M. Gilligan.
Literature Cited (1) Baker, G . L., Food I n d . , 6 , 305 (1934). (2) Cox, R.E., Ibid., 5, 348 (1933). (3) Fellers, C. R.,Am. J. P u b , Health, 23,13 (1933). (4) Morse, F. W., J . Biol. Chem., 81, 77 (1929). (5) Myers, P.B., and Baker, G. L., Del. Agr. Expt. Sta., Bull. 144 (1926). (6) Ibid., 149 (1927). (7) Ibid., 187 (1934). ( 8 ) Nelson, E. K., J . Am. Chem. SOC.,49, 1300 (1927). ENG.CHEM.,Snal. Ed., 6, 143 (1934). (9) Olsen, A. G.,IND. (10) Olsen, A. G., S. Phys. Chem., 38,919 (1934). (11) Spencer, Gene, Ibid., 33,2012 (1929). (12) Tarr, L. Wr., Del. Agr. Expt. Sta., Bull. 142 (1926). R B C ~ ~ I VSeptember BD 23, 1935. Presented before the Division of Agricultural Chemistry at the 90th Meeting of the American Chemioal Society, 6an Francisco, Calif., August I9 to 23, 1936. Publication approved by the Director, Delaware Agricultural Experiment Station.
Specific Heats of Sodium
Hydroxide Solutions
H
EAT balance calculations of processes in-
volving the mixing, diluting, or concentrating of solutions must be based on the specific heats and heats of dilution of the solutions. It has been shown (4) that such thermal data are conveniently assembled in the form of an enthalpy-concentration diagram, or Merkel chart (6),from which items for heat balances are readily taken. When, however, the construction of enthalpy-concentration charts for common commercial chemicals is attempted, it is soon found that the necessary thermal data are usually lacking. As a start towards remedying this lack of data, this paper presents new experimental results on the specific heats of sodium hydroxide solutions over a concentration range of 4.08 to 51.15 per cent of sodium hydroxide by weight, and a temperature range of 3.1" to 88.6" C . (37.5O to 191.3' F.). When combined with data on heats of dilution, which have been presented in another paper ( I ) , the new data allow the construction of an enthalpy-concentration chart over the same ranges of concentration and temperature. The work was done entirely from a practical point of view. No attempt is made to develop or test theories of solutions or to present the data on any but a n empirical basis. Extreme accuracy was not expected, but the results are believed to be of adequate precision for all engineering applications.
Previous Work Specific heats of sodium hydroxide solutions were reported by Thomsen ( I S ) over a concentration range of 1.1 to 23 per 1
Present address, Standard Oil Company of Indiana, Whiting, Ind.
JOHN W. BERTETTII AND WARREN L. McCABE University of Michigan, Ann Arbor, Michigan
cent and a t an average temperature of about 17.5" C. (63.5' F.);by Tucker (14) over a concentration range of 16.5 to 47.4 per cent and a temperature range of 18.9"to 24.0" C. (66.0" to 75.2" I?.); by Pratt (6)over a concentration range of 0.6 to 16 per cent and a temperature range of 0" to 33.3" C. (32" t o 92" F.); by Richards and associates New d a t a , o b (7-11) over a concentrat a i n e d primarily t i o n r a n g e of 0.139 to for industrial use, 27.8 per cent and a temperature range of 15" to are reported on the 20" c). (59" to 68" F.); specific h e a t s of and by Gucker and s o l u t i o n s of soSchminke (3) over a condium hydroxide in centration range of 0.158 water. The measto 8.157 per cent a t a temperatureof 25°C. (77°F.). urements were ob-
Experimental Pro cedure
-
The adiabatic method developed by R i c h a r d s (11) was used. The calor i m e t e r p r o p e r , surrounded b y a ('submarine" was totally imm e r s e d in a bath; the temperature of the bath
tained by the adiabatic method and cover a concentration range of 4 to 51 weight per cent sodium hydroxide and a temperature r a n g e of 37" t o 191" F.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
V/d/,l
FIGURE 1. WORKING CALORIMETER
1 I
1I
VOL. 28, NO. 3
IIIIIIIIIII
IIIIII
r
11
FIGURE 2. COLDCALORIMETER
completely immersed in a bath, K, which is contained in the inner can, S. Can S is lagged by 1 inch of felt, T, which, in turn, is inside outer can V . Reciprocating stirrers, C and D, were operated a t a rate of sixty double strokes per minute. Each stirrer had a short Formica section, g, to reduce heat conduction. Chimneys are shown at M . The quantitative heating element, E, was similar in design to that used by Gucker and Schminke ( 3 ) . An auxiliary heating element, F , was used to bring the calorimeter ra idly to temperaturewhen operating at elevated temperatures,and KeatApparatus ing coil 0 could be used to heat the bath rapidly to the working temperature. Adiabatic control to within *0.02O F. was made The calorimeter was so designed that with a slight modificapossible through use of a differential thermoelement of twentytion it was possible to measure either specific heats or heats four pairs of wires, &, directly connected to a sensitive galvanomeof dilution. All parts which came in contact with the soluter, and the use of electrolytic heating (Id,2). The thermoelement junctions were insulated by a mixture of ultramarine and tions were of pure nickel. All thermoelements were of No. collodion, and were im40 copper and No. 30 mersed in mercury to rec o n s t a n t a n wires and r duce lag. In connection were c o n s t r u c t e d and with electrolytic heating it --A was found that when the used according to the 1 1 submarine itself was used r e c o m m e n d a t i o n s of as an electrode, true adiaWhite (16). batic conditions did not Figure 1 is a diagram prevail when the adiabatic bath thermoelement indiof the calorimeter: cated zero temperature difference. The subVessel A has a capacity marine was a c t u a l l y of about 650 cc. (22 fluid slightly warmer than bath ounces) a n d contains K. This difficulty was the solution undergoing overcome by surrounding investigation. The cover the s v b m a r i n e with a is fastened to the flange, coarse metal grid, N , sepaa,by means of the follower rated from the wall by a ring, b. It is suspended distance of 1.5 cm. (0.59 from the cover of a “subinch) and using this grid marine” v e s s e l , B, by and inner can S as elecFormica hangers, c, . protrodes. The current viding a 4-om. (1.6-mch) COLD CALORIMETER WORKING CALORIMETER through coil E was deterair space between the submined by measuring the marine and the calorimevoltage across a standard F I G U R E 3. THERMOELEMENT SYSTEM ter. The submarine is was maintained, as nearly as possible, equal to that of the calorimeter. The heat input was determined by measuring the voltage and current of an electric heater and the time of heating. Corrections for heat of stirring were found by measuring the temperature drifts before and after the heating period.
MARCH, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
one-ohm resistance. A Leeds and Northrup type K-2 potentiometer was used in all voltage measurements. A period of 600 seconds was used for heating, and the time was measured with a precision of better than 0.01 per cent by means of a pendulum clock and automatic switch. The temperature change of the solution was measured by means of a twenty-four-junction thermoelement, W24. This thermoelement and one of four junctions, to be referred to later, were calibrated by comparison with a platinum resistance thermometer which had been calibrated to =+0.02' F. in this laboratorv at the ice point, steam point, sulfur point, and the transition goint of Na2S04.10Hz0.
TIME IN MIWTES
ia R
:I
3
In order to maintain all potentiometer readings in the lowest range where the sensitivity is 0.1 microvolt, the "cold" junctions of thermoelement Wz4were maintained at a constant temperature above 32" F. by means of a cascade cold calorimeter suggested by White (16). This calorimeter is shown in Figure 2, and Figure 3 shows diagrammatically the thermoelement system: Copper block A (Figure 2 ) is contained in a small vacuum flask, B. Flask B is placed inside a hollow copper block, G, which in turn is placed inside a wide-mouthed 1-liter vacuum flask, D. This vacuum flask is incased in a sheet iron vessel, E , which is, in turn, immersed in a thermostatically controlled bath, F . Each copper block is provided with a resistance heater, and current can be passed through these resistances individually or in series. A sixteen-junction thermoelement, 4 6 , similar t o the twenty-fourjunction element of the adiabatic control, measures the temperature difference between the outer block and the bath. A fourjunction thermoelement, C1, with one set of junctions in an ice bath measures the'temperature of the outer block. A twentyfour-junction thermoelement, D24, measures the temperature difference between the inner and outer copper blocks. Wheqmeasuring the temperature of the solution, thermoelement 0 2 4 is connected in series with the main working thermoelement, Wzr, so that the outer block temperature cancels and the temperature of the inner block becomes the reference for measuring the solution temperature. In Figures 2 and 3 the thermoelements are shown as single junctions to avoid confusion. The junctions are grouped and inserted in holes in the blocks. In operation, the temperatures of the two blocks were e ualized by means of their resistance heaters. The temperature o? bath P was adjusted to the same temperature and maintained at this temperature by means of thermoregulator I and heater K. The bath was stirred vigorously by stirrer L. The temperature of the thermostat was automatically maintained constant within *O.OIOo F. H is an auxiliary cooling coil. At 131" F. and with the thermostat adjusted so that the difference between the two blocks remained zero as indicated by thermoelement Dz( over a 3-hour period, the actual temperature of the blocks as indicated by thermoelement C4 was observed at frequent intervals and found to increase linearly with time at a rate of 0,0003"F. per minute. The rate of increase was greater at higher temperatures. It is possible that chemical action caused the drift since the copper blocks were covered with a light film of oil. No error was introduced in the measurements of temperature changes of the solutions by this linear drift, since it is eliminated in the same manner as the drift due to stirring.
TIME IN MIWTES
FIQURE 4. TEMPERATURE DRIFTS IN RUN
A
TYPICAL
agreed within 0.7 per cent with that found by direct measurement.
Method of Operation From the foregoing much of the experimental procedure may be inferred. With a solution of given concentration, several specific heat determinations were made at different temperatures. The cold calorimeter was first brought to equilibrium a t a temperature about midway in the range to be covered. I n order to correct for the heat of stirring and for the small temperature drift of the cold calorimeter, each experiment consisted of three periods: a fore period, a heating period, and an afterdrift period. Readings of time and e. m. f. of thermoelement W24 0 2 4 were made a t intervals for at least 15 minutes before starting the heating current and for at
+
OF HEATCAPACITY RUNS TABLE I. SUMMARY
NaOH Teight
70
4.081
6.920
21.38
Solutions
29.71
Thermoprene-lined ( I d ) glass, nickel, or monel metal vessels were used in preparing the solutions. Stock solutions were made by first preparing crystalline NaOH.H1O from c. P. stick sodium hydroxide and redissolving the solid to produce a saturated solution a t room temperature. The insoluble sodium carbonate was removed by settling. The solutions were analyzed gravimetrically with an accuracy of *0.005 per cent by the method suggested by Richards and Hall (9).
37,53 50.88
6.80 7.39 8.91 17.70 20.98
Heat Capacity of Calorimeter The heat capacity of the calorimeter was determined electrically, using water, in a manner identical to that used in measuring the heat capacities of the solutions. Measurements were made in a range from 40' to 140" F. At 68" F. the heat capacity was also calculated from the heat capacities and weights of the constituent parts, and the value obtained
377
31.52 37.10 40.44
Temp
' F.
37.62 46.89 68.00 86,OO 39.49 44.89 55.89 76.95 42.73 43.12 50.36 51.66 61.77 69,04 77.31 86,36 46.54 58.21 42.21 49,73 58.55 55.98 68.22 77.90 93.02 67,82 67.69 69.48 67.91 68.47 78.87 68.47 77,ll 86,OO 68.32 77.40 86.40 67.95 77.38 68.29 77.02 86.04
Capacity Heat NaOH Temp. Capacity Heat B. t. u./lb.f' F . Weight $' & F. B.t. u./lb./OF. . . 0.9380 41.48 68.11 0,8126 0.9416 77.02 0.8143 0.9476 86.27 0.8148 0.9523 47.71 68.11 0.7857 0.9113 76.75 0.7840 0.9141 86.11 0,7849 0.9184 5.78 106.18 0.9406 0.9254 122,50 0.9428 0.8465 140.09 0.9454 0.8473 154.27 0 9476 0.8506 11.90 103.80 0.9027 0.8520 124.20 0.9040 0.8566 139.23 0.9089 0.8590 154.67 0.9108 0.8623 19.89 107.10 0.8776 0.8666 120,47 0.8802 0.8286 140.49 0.8840 0.8344 158.38 0.8857 0.8150 29.53 103.78 0.8680 0.8172 122,41 0,8633 0.8208 140.11 0.8676 0.7685 155.41 0.8688 0.7670 39.44 103,05 0.8286 0.7661 105.75 0.8294 0.7651 121.96 0.8320 0.9230 140.14 0.8337 0.9179 156.11 0.8348 0.9184 About 44% 81.59 0.8036 0,9070 not ana- 103.48 0.8052 122.18 lyaed 0.8067 0.8695 0.8731 51.15 122.22 0.7606 140,04 0.7596 0.8607 165.77 0.7587 0,8645 0.8683 142.32 45 20 0.7997 0.7981 157.37 0.8372 0.7971 176.27 0.8413 0,8451 0.7744 150.67 48.70 176.32 0.7728 0,8248 0.7723 191.37 0.8280 0.8153 0.8179 0,8198
INDUSTRIAL AND ENGINEERING CHEMISTRY
318
HEATSOF SODIVM HYFROXIDE SOLUTIONS TABLE11. SPECIFIC F. IN B. T. u. PER POUND PER Wei ht Per 8ent ,-NaOH 32 40 50 0 1.034 1.003 1.001 2 0.965 0.967 0.968 4 0.936 0.940 0.943 6 0.914 0.920 0.924 8 0.897 0,902 0.907 10 0.882 0.888 0.893 12 14 16 18 20 22 24 26 28 30 32 34 . . 0.823 36 0.819 38 ... . . . 0.816 40 ... . . . 0.812 42 0.807 44 ... . . . 46 ... ... 48 50 52 ..,
.. .. .. ... ... ... ... ... ...
. .. . ...
... ...
.. .. .. ...
60 0.999 0,969 0.946 0.928 0,911 0.897
0.828 0.824 0.820 0.815 0.809 0.802
0.793
... ... ...
Temperature, 80 100 0.998 0.997 0.972 0.974 0.951 0.954 0.933 0.938 0.918 0.923 0.905 0.911 0.894 0.901 0.886 0.892 0,880 0.886 0.873 0.880 0.868 0.875 0.863 0.870 0.858 0.866 0.854 0.863 0.850 0.859 0.846 0.855 0.842 0 850 0.837 0.845 0.832 0.840 0.827 0.833 0.821 0.826 0.813 0.816 0.804 0.806 0.794 0.795 0.783 0.782 0.771 0,769 0.758 0.756
F.: 120 0.998 0.977 0.957 0.941 0.927 0.916 0.906 0.897 0.891 0.885 O
0.880
0.876 0.873 0.869 0.866 0.862 0.857 0.852 0.845 0.837 0.829 0.819 0.807 0.794 0.781 0.768 0.755
140 0.999 0.978 0.960 0.944 0.930 0.918
0,909 0.901 0.894 0.888 0.884 0.880 0.877 0.874 0.870 0.866 0.862 0.856 0.849 0.841 0.831 0.819 0.807 0.794 0.780 0.767 0.754
least 20 minutes after stopping the current. On plotting these points and extrapolating the nearly parallel lines so obtained to the middle of the heating period, the difference in e. m. f. values a t this point gave the true change in e. m. f. due to the electrical energy input. The trend of the afterdrift immediately after stopping the heating current indicated that the temperature of the metal parts of the calorimeter lagged perhaps 0.04"to 0.05' F. behind that of the solution. Figure 4 shows the e. m. f. us. time curves for a tyDical run in which t 6 e h e a t i n g wa s started a t time 37 minutes and stopped a t time 47 minutes. The decreasing values of e. m. f . with time were due to the fact that the cold junctions of thermoelem e n t W24 4- 0 2 4 I were at a higher 1 1 1 1 I\-, 1 I ,'\i temperature t h a n 091 I t h o s e in the solution. A s m a y be seen from Figure 4, the temperature of the solution in the region of thermoelement Wzd decreased slightly i m m e d iately after stopping the heating current. The d i s t a n c e A B r e p r e s e n t s a temperature difference of a p p r o x i m a t e l y 0.02" F., and this temperature change is accounted for by the equalization of temperature after 0 5 10 15 20 25 30 35 40 45 Y) WElGHT PER C E H l NaOH. the heating current was turned off. FIGURE 6. COMPARIEON O F SPECIFIC Eighty per cent HEATDATA ~~
160 1.000 0.980 0.962 0.946 0 932 0.920 0.911 0.903 0.896 0.890 0.886 0.882 0.879 0.875 0.872 0.868 0.863 0.857 0.850 0.842 0.832 0.820 0.807 0.793 0.779 0.765 0.753
180 1.002 0.983 0.965 0.948 0.934 0.922 0.912 0.903 0.897 0.891 0.886 0,882 0.879 0.876 0.872 0.869 0.864 0.858 0.851 0.842 0.832 0.820 0.806 0.791 0.777 0.765 0.752
200 1.004 0.986 0.966 0,950 0.936 0,923 0.913 0.904 0.897 0.891 0.887 0.883 0.880 0.876 0.873 0.869 0.864 0.858 0.851 0,843 0,832 0.820 0.804 0.789 0,776 0.764 0,752
VOL. 28, NO. 3
of the calculated evaporation correction was applied to measurements in which evaporation inside of vessel A was appreciable, although the correction was in any case very small.
Results of Measurements
The results of eighty-one measurements are shown in Table I. Few measurements were made above 158"F., but it was found that above 140" F. the heat capacities were practically independent of temperature so that little uncertainty was involved in extrapolating to higher temperatures. The temperature coefficient of the heat capacity near 32' F. is of considerable magnitude and changes rapidly with temperature so that extrapolation to 32" F. was comparatively unsatisfactory. The heat capacities were converted to B. t. u. per pound per " F., were cross-plotted on a l a r g e s c a l e , and were rounded to even values of concentration and temperature. The results are given in Table 11. The conversion factor used was 4.1876 joules per gram calorie,
Comparison with Previous Work Figure 5 shows a comparison of the heat capacity values of Richards and Gucker (8) a t 68" F. with those of the present work a t the same temperature. The agreement is well within the probable precision of the measurements. A similar comparison was made with the specific heats measured by Gucker and Schminke (3) a t 77" F. The maximum difference found was 0.13 per cent a t a concentration of 4 per cent. In Figure 6 are plotted the specific heat data of Tucker (1.4) at a mean temperature of 68" F., of Thomsen (IS) a t a mean temperature of 63.5"F., and those of the present work a t 68" F. Thornsen's values would be increased slightly if corrected to 68" F., so his work is in good agreement. Tucker's data, over a considerable concentration range, lie on a curve almost parallel with, but considerable lower than, that of the present work. Apparently an almost constant error entered into his results.
Literature Cited (1: Bertetti and McCabe, IND.ENG.CHEM.,28, 247 (1936). (1A) Daniels, J . Am. Chem. SOC.,38, 1473 (1916). (2) Derby and Marden, Ibid., 35, 1767 (1913). (3) Gucker and Schminke, Ibid., 55, 1013 (1933). (4) McCabe, Trans. Am. I n s t . Chem. Engrs., 31, 129 (1935). (5) Merkel, 2. Ver. deut. Ing., 72, 109 (1928). (6) Pratt, J. Franklin Inst., 185, 663 (1918). (7) Richards and Gucker, J . Am. Chem. SOC., 47, 1876 (1925). (8) Ihjd., 51, 712 (1929). (9) Richards and Hall, Ibid., 51, 707 (1929). (10) Ibid., 51, 731 (1929). (11) Richards and Rowe, Ibid., 43, 770 (1921). (12) Soule, IND.ENG.CHEM.,Anal. E d . , 1, 109 (1929). (13) Thomsen, Ann. Physik, 142, 337 (1811). (14) Tucker, Trans. Roy. SOC.(London), A215, 319 (1915). (15) White, J . Am. Chern. SOC., 36, 2292 (1914). (16) White, "Modern Calorimeter," p. 131, New York, Chemical Catalog Co., 1928. RECEIVED August 3, 1935. Abstracted from a dissertation submitted by John W. Bertetti i n partial fulfillment of the requirements for the degree of doctor of philosophy, University of Michigan.
