INDUSTRIAL AND ENGINEERING CHEMISTRY
296
rubber compound a t least the early stagcs of oxidation will place it in one of the three groups; its subsequent behavior can be anticipated accordingly. Similar curves are being determined for the synthetics. Where the rubber in the compound is protected from light by enough carbon black or ferric oxide, exposure to a n ozonecharged atmosphere alone, without illumination, is sufficient; and the compound is rated in terms of time taken to crack, as compared with the reference compound, for a given concentration of ozone. There is a pitfall in this connection, however, especially in the case of GR-S compounds. In a high-quality GR-S compound such as a cable jacket, as little as 2Y0 of an effective wax will, a t 25% elongation and a t room tempeiature, protect the compound for weeks from ozone of a concentration as high as 100 parts per hundred million. Discrimination between this and larger additions of wax is therefore not po-sible in such circumstances. Differences do appear a t higher elongation-hence the need for observations a t different degrees of stretch. Raisin:, the temperature also shows up diffcrcnces in wax coilcentration, and there are indications that reasonable discrimination can be made in this way. This fcature is now under study. These tests can lead t o reliable conclusions as to the weatherability of a rubber compound, but experience and good judgment are still called for in making such appraisal.
Vol. 38, No. 3
IJTERATURE CITED
(1) Asano, K., India-Rubber J . , 70,389 (1925). (2) Barton, B. C. (to U. S. Rubber Co.), U. S. Patent 2,324,056: (July 13, 1943). (3) Coleman, C., Ibid., 2,246,932 and 2,306,779 (1942). (3-A1 Dobson, G. B. M., Proc. Rou. SOC.(London). A129, 416 (1930). (4) Ellis, Carleton, \Veils, A. rl., and Boehmer, Norris, "Cherniea1 Action of Ultra-violet Ravs". Chao. 31. Xew York. Reinhold Pub. Coip., 1926. (5) Farmer, E. H., et al., J . Ciiem. Soc., 1942, 116, 139; 1943, 119 122, 125, 541. (6) Goodeve, C. F., Trans. Faraday Soc., 33, 340 (1937). (7) Greenbank, G. R., and Holm, 0.E., IXD.ENG.CHEX.,33, lOB!! (1941). (8) Ingmanson, J. H., and Kemp, A. R., I b i d . , 30, 1168 (1938). (9) Kemp, .A. R., Ingmanson, a. H., and Mueller, G. S., Ibid., 31, 1472 (1939). (10) Lewis, S. J., and Porritt, U:D., J . SOC.Chem. Ind., 40, 18T (1921). (11) Luckiesh, >I., et al., J . F ~ a n k l i Inst., n 223, 699 (1937). (12) Moon, P., Ibid., 230, 583 (1940). (13) PaAeth, F. A., and Edgar, J. L., Nature, 142, 112 (1938). (14) Reynolds, 1%'. C., J . SOC.Chem. Ind., 49, 168T (1930). (1.5) Scheibe, G., and Pumrnerer, R., Ber., 60, 2163 (1927). (16) Turner, H., T r a m . Inst. R u b b e r l n d . , 10, 21 (1934). Karctschuk, 7, 79, 115 (1931). (17) Van Rossem, A,, and Talon, H. W., 18, 367 (1926). (18) Williams, Ira, IND.ESG.CHEM., (19) Wood, L. A , J . A p p l i e d P h y s . , 12, 119 (1941).
The System Ammonium NitrateAmmonia-'Water J
PARTIAL VAPOR PRESSURES AND SOLUTION DENSITIES J. F. SHULTZ AND G . V. ELNIORE Tennessee Valley Authority, Wilson D a m , Ala. T h e total vapor pressures of solutions in the system ammonium nitrate-ammonia-water were measured at 10 ' and 35' C., the vapor phases were analyzed by a thermal conductivity method, and the corresponding partial pressures of ammonia and water were calculated. The experimental compositions contained from 5 to 30Oj, ammonia and from 0 to 75% ammonium nitrate. The densities of the solutions were determined at 35' C.
1
STUDIES of liquid media for the distribution of agricultural nitrogen, information was needed on the vapor pressures and densities of solutions in the system ammonium nitrate-ammoniawater. Pertinent published information was confined t o related binary systems. Vapor pressures in the system ammonia-water were measured by Perman (6, Y),arid the data of several investigators were reported by Kracek (4) ; densities in this system were measured by Mttasch, Kuss, and Schlueter ( 5 ) ,and similar data of other investigators are compiled in the International Critical Tables (5). The densities of several solutions in the system ammonium nitrate-water were measured by hdams and Gibson (1) and by Arbo-Hoeg (a), The present paper describes the measurement of the partial vapor pressures of solutions in the system ammonium nitrateammonia-water a t 10" and 35' C. and the determination of the densities of these solutions a t 35' C. The experimental compositions contained from 5 to 307, ammonia and from 0 t o 75Yo ammonium nitrate. Adaptability of the experimental results t o interpolation was ensured by measuring the vapor pressure of
several series of ternary compositions containing constant proportions of ammonium nitrate and water. PREPARATIOS' OF SOLUTIONS
The solutions were prepared with distilled water that had been degassed. The liquid ammonia used in the solutions was essentially pure; it contained 0.01% oil and 0.04% water. The ammo-. nium nitrate was purified by recrystallization. It was found convenient to prepare a series of aqueous am-. monium nitrate solutions to which increments of ammonia could be added. The ratios of ammonium nitrate to water were 24.9 to 75.1, 49.9 to 50.1, and 75.1 to 24.9. The ammonium nitrate solutions were stored in closed vessels. The solution containing the highest proportion of ammonium nitrate was stored a t 60' C. t o prevent the separation of a solid phase. The concentration of ammonium nitrate in thc solutions was detecmined by t,he formaldehyde method (9). The t,ernary compositions were prepared in a flask from which they could be transferred directly to the vapor pressure apparatus or to the density apparatus. To a definite weight of ammonium nitrate solution in the tared flask, liquid ammonia was added carefully and slowly until a chosen total weight of solution was approximated. A stopper, bearing an outlet tube with :I stopcock and the female portion of a ground joint, was claniped into the mouth of the flask, the whole n-as weighed to the nearest centigram, and the composition of the system was calculatcd. The concentrations of ammonia found in spot checks by chemical analysis were within 0.1 7, of the concentrations calculated from
March, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY CLOSED -END MANOMETER
c
€QUI LIBRATION CHAMBER AND
MAGNET!C STIRRER
297
The analyzer was calibrated a t 100 mm. pressure with mixtures of water vapor and ammonia in known proportions. These mixtures were prepared in the vapor pressure apparatus. The apparatus was evacuated to 10-8 mm., and vapor from degassed distilled water was admitted t o the equilibration chamber a t 35" C. After the pressure of the water vapor had been read from the manometer, the vapor was isolated in a bulb that had been temporarily introduced between two stopcocks just below the glass pump. The remainder of the system was re-evacuated, and dry ammonia gas from redistilled liquid ammonia was admitted t o the equilibration chamber. After the pressure of the ammonia had been measured, it was isolated in the equilibration chamber and the system again evacuated. The water vapor and ammonia were then mixed by filling the equilibration chamber with mercury and circulating the gas by the pump until the reading of the recording potentiometer became constant. Finally, the pressure in the system was adjusted to 100 mm. and the calibration point was read from the potentiometer, The results of measurements made with a series of water vapor-ammonia compositions showed that the reading of the potentiometer was a linear function of the volume percentage of water vapor.
TABLE I. CONSTANTS IN EQUATIONS REPRESENTJNG THE CONCENTRATION A
Wt. Ratio, NH4NOa: Ha0 0:100 24.9:76.1 49.9:60.1 76.1:24.9
Figure 1.
AMMONIA IN
THE
VAPOR
P H A S E AS
Constant A 100 c. 350 c. 0.0162 0 0368 0 0121 0.0263 0 0088 0.0152 0.0103
....
Constant B 100 c. 350 c. 0 00956 0 00910 0 00966 0.00932 0 00974 0 00959 ..... 0.00963
Apparatus for, Measuring Partial Pressure of Ammonia and Water
the weights. Analysis for the ammonia was made by introducing the solution well beneath the surface of a weighed amount of standard sulfuric acid, weighing the combined solutions, and titrating the excess acid. MEASUREMENT OF VAPOR PRESSURE
. I
OF
FUNCTION OF THAT IN THE LIQUIDPHASE
Figure 1 shows schematically the apparatus used in determining the,partial vapor pressures. It consisted basically of a n equilibration chamber which contained the tRst solution a t constant temperature and which communicated, through stopcocks, with a closed-end mercurial manometer for measuring the total pressure and with a thermal conductivity analyzer for determining the proportions of water vapor and ammonia in the vapor phase. The test solution was manipulated within the apparatus . by displacement with mercury. The vapor phase was circulated through the analyzer by means of a glass pump (8) and interconnecting lines which were maintained at 50" C. t o prevent condensation. The temperature of the equilibration chamber was maintained constant within *0.05' C . by a water jacket through which water from either of two reservoirs (thermostatically controlled a t 10" or 35" C.) was rapidly circulated by a smallTotary pump. With this arrangement, rapid change from one temperature t o the other was possible. Rapid attainment of equilibrium between the liquid and vapor phases was facilitated by a magnetic stirrer in the equilibration chamber. A Leeds & Northrup 7801-A-S double-flow gas analyzer was adapted to the analysis of the vapor phase by measurement of the thermal conductivity of the vapor. The flexible connections on the measuring cell were replaced with ground-glass joints (Figure 1) for attachment t o the source of vapor, and the reference cell was sealed while containing dry ammonia a t 1 atmosphere pressure. The temperature of the air bath surrounding the cells was maintained a t 41.5' =t0.1" C. The difference between the respective conductivities of the two cells was measured by a Micromax alternating-current recording potentiometer.
I n the measurement of the vapor pressures of the ternary compositions, the apparatus (Figure 1) was first evacuated t o lo+ mm. About 150 grams of the experimental solution were then transferred directly from the flask in which i t had been prepared t o the solution storage bulb and thence t o the equilibration chamber. By alternate lowering and raising of the solution i n the equilibration chamber, successive boiling of the solution and reabsorption of the liberated ammonia gas were induced, with the result that the small amount of dissolved air originally present in the solution was trapped in a small pocket at the top of the chamber. The air, together with a negligible amount of ammonia, was removed by momentary evacuation E q u i l i b r i u m between the liquid and vapor phases was established by bonnecting the equilibration chamber t o the circulatory system, stirring the solution at-35" C., and pumping the vapor through the analyzer until the potentiometer g a v e a c o n s t a n t reading. A f t e r t h e t o t a l pressure had been read from the manometer, the vapor phase was isolated from the liquid phase, and its pressure PYCNOMETR was adjusted t o t h a t at which t4e analyzer had been calibrated (100 mm.). The reading of the potentiometer then was compared with the calibration chart t o deter~i~~~~ 2. A~~~~~~~~ for. mine the composition of the Measurement of Density 1 vapor phase. The tempera-
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Vol. 38, No. 3
DISCUSSION OF RESULTS TABLE
PRESSURE, P A R T I A L PRESSURE, AND DENSITY 11. TOTAL IN THE SYSTEM SH4NOD-NH,-H~0AT 35 C. O
Compn. of S o h Wt. % NHa NHdNOs 5 47.4 71.3 10 0 22.4 44.9 67.6 0 l5 21.2 42.4 63.8 20 0 19.9 39.9 60.1 25 0 18.7 37.4 30 0 17.4
s"
in
G~~ phase, 1'01. % 79.1 87.0 78.2 83.7 90.0 93.8 86.6
90.3 94.3 96.9 91.4 94.0 96.6 98.6 94.6 96.4 98.0 96.8 98.1
Vapor Pressure, Mm. HgPartial Partial Total of NH3 of H20 135 107 28 22 173 151 41 189 148 182 35 217 26 257 231 21 336 315 301 261 40 348 314 34 421 397 24 552 535 17 465 425 40 534 502 32 628 22 650 842 12 854 37 678 641 762 28 790 933 19 952 32 998 966 1128 1107 21
Density, G./Cc.
1.167 1.276 0.950 1.031 1.121 1.218 0.931 1.003 1.078
1,164
0.914 0.977 1.040 1.113 0.898 0.952 1.004 0.881 0.928
ture of the liquid phase was lowered to 10" C., and measurements of the total pressure and the composition of the vapor phase were made by a procedure analogous to that employed a t 35" C. I n the present work the total pressures were read from the manometer by means of a mirror scale. The readings invariably agreed within * 1.0 mm. with those obtained in previous, unpublishedwork inwhich the total pressures were read with a cathetometer. MEASUREMENT O F DENSITY
The apparatus for measuring the densities of the solutions consisted essentially of a pycnometric bulb of about 20 ml. capacity and a n expansion bulb of about 10 ml. capacity. The tT7-o bulbs were connected as shown in Figure 2. The solution under test was heated to 35" C. in the flask in which it had been prepared and was transferred directly to the tared density apparatus. The apparatus was filled to a point slightly above the central stopcock (Figure 2 ) . For solutions having a vapor pressure greater than the atmospheric pressure, the upper stopcock was manipulated to maintain a positive pressure in the apparatus and thus prevent boiling of the solution. The temperature of the apparatus and its contents was brought t o 35" * 0.05" C. in a water bath, the central stopcock was closed, and the upper stopcock was removed. The solution that had expanded into the portion of the apparatus above the central stopcock was carefully removed, and the apparatus n-as reassembled and yeighed. From the net weight of solution and the known volume of the pycnometric bulb, the density of the solution was calculated.
TABLE 111. TOTAL AND PARTIAL PRESSURES IN XHJJO3-NH3-HzO AT 10" C. Corn n of SOln., % NHs NHiNOa 0 lo 22.4 44.9 15 0 21.2 42.4 20 0 19.9 39.9 25 0 18.7 37.4 30 0 17.4 34.9
kt.
NHa in Gas Phase, Vol. yo 89.4 92.0 94.2 94.0 95.5 96.8 96.4 97.4 98.2 98.0 98.6 99.1 99.0 99.4 99.7
THE
SYSTEM
A study of the results obtained by analysis of the vapor phase showed that the ratio of the lveight percentage, x, of ammonia in solution to the volume percentage, y, of ammonia in the vapor phase in equilibrium with the solution bore a straight-line relation to the \%-eightpercentage of ammonia in solution, both for the ternary compositions and for t,he ammonia-water solutions. Hence, by the method of least squares, it was possible to develop equations of the form, x/y = A
+ BX
by means of which the composition of the vapor phase could br interpolated from the measured values. Table I gives derived values for constants A and B. These equations fitted the experimental data with an accuracy of *0.60/, ammonia in t,he vapor phase. Tables I1 and 111 present interpolated values for the total vapor pressures and for the partial pressures of ammonia and water a t 10" and 35' C. The measurements of total pressures from which these data were derived were made with a prccision of =t1 mm. The tabulated data for the partial pressures generally are rounded to three figures for ammonia and to two figures for watel. The total pressures in Tables I1 and 111 for the system ammonium nitrate-ammonia-water agree closely with the data of Kracek ( 4 ) and of Perman ( 6 ) for the binary system ammonia-ivater. The tabulated partial pressures of ammonia for the binary system arc within experimental error of the values obtained by Perman ( 7 ) a t 10" C. At 35' C. Perman's partial pressures for ammonia generally are higher than t,hose obtained in the present work. Perman's values for total pressures by addition of the two partial pressures generally were higher, however, than the corresponding values he obtained by- an independent method. Densities of the solutions a t 35" C. are given in the last column of Table 11. The measurements from which the data for the ternary system were interpolated were made with a precision of +0.001 gram per cc. The densities given for the system ammonia-water were extrapolated from data of International Critical Tables (5)and of Nittasch, Kuss, and Schlueter ( 5 ) . The tabulated densities for the ternary system are in good agreement with values interpolated from the data of Adams and Gibson ( 1 ) and of Arbo-Hoeg ( 2 ) for ammonium nitrate-u.ater solutions. LITERATURE CITED
(1) Adams, L. H., and Gibson, R. E., J . A m . Chem. Soc., 54, 452036 (1932). ( 2 ) Arbo-Hoeg, F. M., 2. anal. Chem., 81, 114-16 (1930). (3) International Critical Tables, Vol. 111,p. 59 (1928). (4) Kracek, F. C., J . Phys. Chem., 34,499-521 (1930). ( 5 ) Mittasch, A., Kuss, E., and Schlueter, H., 2. anorg. allgem Chem., 159, 1-36 (1926). (6) Perman, E. P., J . Chem. Soc., 79, 718-29 (1901). (7) Ibid., 83, 1168-83 (1903). (8) Porter, F., Bardwell, D. C., and Lind, S. C., IND.EN@. CHEM.. 18, 1086-7 (1926). (9) U. S. Army Specification 50-11-59D, Feb. 6, 1942.
Vapor Pressure, Mm. H g Partial Partial of NHa of He0
Total 54.5 68.5 82.0 92.5 112 137 150 173 215 230 264 321 349 388 446
48.7 63.0 77.0 87.0 107 133 145 169 211 225 260 318 345 386 445
5.8 5.5 4.8 5.5 5.0 4.4 5.4 4.5 3.9 4.6 3.7 2.9 3.5 2.3 1.3
Pure Hydrocarbons from PetroleumCorrection I n the January, 1946, issue, this paper by Griswold, Andres, Van Berg, and Kasch had an unfortunate error in the Literature Cited on page 70. Authorship of four articles (11) from a symposium on aaeotropic and extractive distillation is erroneously ascribed t o Happel, Correll, Eastman, Fowle, Porter, and Schutte. The writers of the papers in question are R. R. White, H. G. Drickamer, G. G. Brown, H. H. Hummel, C. L. Dunn, R. W. LIiller, G. J. Pierotti, R. X. Shiras, and M o t t Souders, Jr.
