INDUSTRIAL AND ENGINEERING CHEMISTRY
932
Vol. 16, No. 9
Vapor Pressure Curves for Systems Containing Alcohol, Ether, and Water'*' By E. A. Louder, T. R. Briggs, and A. W. Browne CORWELL UNIVERSITY, ITHACA, N. Y.
the pressure bulb, and the N CONNECTION with A conoenient apparatus for determining oapor pressure has been manometer was mounted the problem of recoverdescribed. The oapor pressures of certain mixtures in the following beside a boxwood meter ing the solvents used in systems have been determined between 0 and 50 C.: diethyl ether. scale. Two complete pieces the manufacture of certain ethyl alcohol; diethyl ether, ethyl alcohol, water; diethyl ether, of apparatus were employed explosives, a study of the ethyl alcohol, water, diphenylamine. in the investigation. pressure-temperature d i a The oapor pressures of purified diethyl ether, ethyl alcohol, and The temperature was congram in various two, three, water have been redetermined between 0 and 50 C. From the data trolled by immersing the and four-component sysnressure-temnerature curves have been constructed. pressure bulb in a water bath tems has been undertaken to a point above the stopin this laboratory. The investigation has comprised determinations of the pressure- cock, IS,the bath being stirred thoroughly during each detertemperature curves over a range from 0" to 50" C. for the mination. The temperature of the bath was maintained a t the systems (1) diethyl ether, ethyl alcohol; (2) diethyl ether, desired point without the use of an automatic thermoregulatethyl alcohol, water; (3) diethyl ether, ethyl alcohol, water, ing device, one of the operators either making small additions of ice or heating the water with a nichrome coil, according to diphenylamine. the temperature desired. It was found that this method MATERIALS sufficed to keep the temperature constant to within 0.02" C. DIETHYLETHER-Diethyl ether was shaken with concen- over the period of time required for a pressure determination. trated sodium hydroxide, and after being dried, first over During this period the pressure bulb, connected with the anhydrous calcium chloride and then over sodium, it was a t manometer through the flexible glass spiral, C, was steadily length distilled for use from a flask containing sodium. The shaken, for the purpose of bringing about, as rapidly as posnormal boiling point was found to be 34.60' C. sible, the necessary condition of equilibrium between liquid ETHYLALcoHoL-Technical absolute alcohol was boiled for and vapor. 10 hours with anhydrous calcium oxide, distilled, and again All thermometers used in this investigation were compared boiled with anhydrous calcium oxide for an additional period with a standard thermometer recently calibrated by the Buof 48 hours. After being distilled, the alcohol was freed from reau of Standards. The readings were corrected for stem aldehyde by treatment with dry silver oxide. It was then immersion when necessary. All readings of barometer and boiled for 48"hours with anhydrous barium oxide and was manome.ters have been reduced to 0" C. and are expressed in finally distilled for use from a flask containing sodium. The millimeters of mercury. normal boiling point was found to be 78.36" C. PROCEDURE WATER-water of special purity was prepared by distillation from a potassium dichromate solution. The steam was After the apparatus had been supplied with a sufficient passed through a calcium hydroxide solution to remove car- quantity of redistilled mercury, the pressure bulb was placed bon dioxide, and the condensate was stored in a closed con- in communication with the external atmosphere through the tainer. APPARATUS The vapor pressure apparatus is shown in Fig. 1. The pressure bulb, R,containing the system under investigation, the manometer, M , the leveling tube, L, and the water bath, A , comprise the essential features. The liquid to be studied was stored in the reservoir, K , which in turn was protected by the glass-stoppered U tubes, T and T', containing, in order, phosphorus pentoxide and anhydrous calcium chloride. To prevent distillation of the volatile liquid from the reservoir into the desiccants, care was taken ordinarily to close the connection between the two by turning the stopper in T . The pressure bulb could be placed into communication with the storage reservoir via the ground-glass joint a t J, or it could be connected with the external atmosphere through a soda-lime tower, T ". The leveling bulb was fitted with a glass plunger for the delicate adjustment of the mercury level in
I
O
O
O
Received April 25, 1924. article is based upon the thesis presented to the faculty of the Graduate School of Cornell University by E. A. Louder in partial fulfilment of the requirements for the degree of doctor of philosophy. The work w a s undertaken a t the suggestion of Major J. H. Hunter, Ordnance Department, U. S. A., and has been supported by a grant from that department. It is now published with permission of the Chief of Ordnance. Acknowledgment is here made of the assistance rendered by A. B. Hoe1 in certain parts of the experimental work.
O
1
* This
FIG.1
soda-lime tower, T " , and the mercury level was brought to a fixed point in the narrow connecting tube below B, as shown in the sketch, This adjustment was made by bringing the
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
September, 1924
level of the mercury exactly opposite a definite line on the scale D,which consisted of an inverted buret held firmly i n position in the supporting framework of the apparatus and bearing calibration marks which passed entirely around the stem. By ascertaining the position of the mercury level in the manometer, a reading of the latter was obtained when the vapor phase in the pressure bulb consisted simply of the dry air under barometric pressure.
933
were taken to eliminate the dissolved air carried by the liquid. This was done conveniently by lowering the mercury level until a fairly large volume of vapor was formed above the liquid in the pressure bulb, when, on causing this vapor to be condensed by a sudden increase in pressure, a portion of the air carried into the vapor remained uncondensed and was trapped in the form of a bubble below the stopcock S, through which it was expelled. This process was repeated several times until no visible trace of uncondensable gas remained. The mercury level in the pressure bulb was finally brought opposite the fixed point on the buret scale and the manometer reading was obtained, after due care had been taken to bring liquid and vapor into complete equilibrium. The difference between this closed-bulb reading and the open-bulb reading previously obtained was subtracted from the barometric pressure. The result was the vapor pressure of the liquid. TABI.E 11-VAPOR Temperature
c.
0.0 5.0 10.0 15.0 20.0 26.0 30.0 35.0 40.0 45.0 50.0
New data 12.41 17.31 24.34 33.22 44.40 59.7 79.3 103.1 134.6 173.3 221.1
ALCOHOL Data by Ramsay Data by and Young Regnault 12.24 12.70 17.60 17.30 24.20 23.77 3 2 . Sn 33.00 44.50 44.00 59.40 5 8 . 8 (curve) 78.50 78.06 1 0 2 . 0 (curve) 102.90 133.42 133.70 172.0 (curve) 172.20 219.82 219.9
PRESSURE OF
Certain special precautions should be mentioned. Owing to the fact that the mercury in the spiral below the pressure bulb was at the temperature of the water bath while the rest of the mercury in the apparatus was a t the temperature of the room, the open-bulb readings varied slightly as the temperature of the water bath was changed. Since the temperature of the room remained practically constant, it was found to be sufficient, however, to determine once for all the open-bulb readings for each apparatus over the whole temperature
The pressure bulb was then filled completely with mercury, the stopcock was closed, and mercury was withdrawn until its level was again brought opposite the fixed point on the buret scale. The difference between the manometer reading now obtained and the previous reading should, of course, be equal to the height of the barometer, and since this was found to be true within 0.2 mm., the apparatus was considered to be in satiSfactory working condition. The actual measurement of vapor pressure was thereupon begun. A definite quantity of liquid was drawn into the pressure bulb from the storage reservoir, and the bulb was placed in communication with the atmosphere as before. After adjusting the temperature of the water bath to 0" C., the mercury level was brought opposite the fixed point on the buret scale and the manometer reading was obtained, this time with the bulb containing air and volatile liquid under barometric pressure. For the sake of convenience, this will be called an open-bulb reading. TABLE I-VAPOR Temperature 0
c.
:E
10.0 15 0 20.0 25 0 30 0 35.0 40.0 45 0
JO 0
New data 185.3 233.2 291.7 360.7 442.2 537.0 647.3 775.5 921.3 1089,8 1276.4
PRESSURE O F
ETHER
Data by Ramsay and Younn 184.9 2 3 2 , 5 (curve) 291.78 361,O (curve) 442 36 5 3 7 . 5 (curve) 647.92 776 .O (curve) 921.18 1091.5 1276.11 I
Data by Reanault 184.4 230.9 286.2 353.6 432.8 525.9 634.8 761.2 907.0 1074.5 1264.8
The nir above the liquid was next expelled by raising the level of the mercury, the stopcock was closed, and steps
range (0' to 50" C.), and to use the data thus obtained t o correct the open-bulb readings determined once only a t 0" C. for each single liquid or liquid mixture investigated. It was found, for example, that the open-bulb reading for apparatus No. I changed 0.4 mm. for a rise of 10" C. I n any given series
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
934
ETHER
O F ALCOHOLAND PRESSURES O F MIXTURES (A = alcohol; E = ether) 39.934, A 30.46% A. 19.93% A 50% 4 69.917 A 50% E 60.07% E 68.54% E 80.07% E 30.09d E 160.8 141.1 151.7 93.7 111:s 126.7 178.1 190.5 203.6 158.5 139.5 118.1 221.7 236.8 197.9 253.9 175.0 147.2 271.2 293.6 247.9 314.4 215.5 182.1 359.2 384.4 268.1 332.9 302.7 224.8 467.5 324.5 405.2 436.1 367.8 274.0 566.9 529.2 395.3 491.7 446.2 333.9 681.7 632.1 476.7 590.6 536.4 403.7 812.2 571.0 708.6 641.5 758.0 486.2 965.2 679.2 842.8 762.1 901.0 582.0 1136.D 804.6 995.0 903.5 1062.7 693.2
TABLE111-VAPOR Temperature C. 0.0 5.0 10.0 15.0 20.0 28.0 30.0 35.0 40.0 45.0 50.0
Pure alcohol 12.41 17.31 24.34 33.22 44.40 59.7 79.3 103.1 134.6 173.3 221.1
89.96% A 10.04% E 43.3 54.6 70.1 89.2 112.4 140.7 174.8 217.3 266.3 327.4 400.3
79.237 A 20.07d E 70 :9 90.2 114.4 144.5 174.0 214.2 262,9 318.5 386.6 467.1 558.1
Vol. 16, No. 9
%%
of determinations, of course, the open-bulb reading depends upon the height of liquid contained above the mercury in the pressure bulb; but since the latter remained very nearly unchanged during each series of pressure determinations for a given liquid over the temperature range, the open-bulb
9 977' A 9 0 : 0 3 4 E' 172.0 217.0 271.7 335.7 410.8 499.3 604.4 726.2 865.8 1025.8 1208.4
Pure ether 185.3 233.2 291.7 360.7 442.2 537.0 647.3 775.5 921.3 1089.8 1276.4
more volatile components, the vapor phase in equilibrium with the liqui6 differs from the latter in composition, unless the mixture chances to be azeotropic. The act of vaporizing the liquid mixture in the pressure bulb will therefore change the composition of the liquid phase by an unknown amount, which may be relatively great where one of the rolatile components is present in only a small proportion. Steps were therefore taken in this investigation practically to eliminate this source of error by using a large volume of liquid in the pressure bulb in contact with a comparatively small volume of vapor. TABLEVI-VAPOR
PRESSURE O F
MIxTunEs
OF
ALCOHOL, ETHER, AND
DIPHENYLAMINE
(A = alcohol, E = ether, D = diphenylamine) 33'/s% 331/3% (99.7% E; 0.3% D) (99.4% E;O.B%D) 33' 3 % E Temperature 662/3% A (95%) 6sn/3% A (93%) 661/a'%A (95%) c. 99.3 102.2 100.1 0.0 124.5 127.4 5.0 155.7 165:5 158.8 10.0 191.8 193.9 196.1 15.0 236.3 237.6 240.9 20.0 288,3 290.0 293.1 25.0 351,8 353.3 357.6 30.0 424.9 427.2 431.2 35.0 516.6 514.4 518.5 40.0 612.0 614.1 620.6 45.0 731.0 728.7 737.5 50.0
The various mixtures were prepared by measuring, with tha aid of burets calibrated by the Bureau of Standards, the requisite volumes of the purified components, the density of which had been determined previously with great care. The mixtures were produced directly in the reservoir K in such wise as to prevent any appreciable loss through volatilization. EXPERIMEXTSI,
reading a t 0" C . , plus the corrections, could be employed without any sensible error. This point was substantiated by a separate experiment. When the liquid under investigation is a mixture of two or Temperature
c.
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
The effectiveness of the apparatus and of the experimental method was first tested by determining separately the vapor pressures of two of the individual components, diethyl ether and alcohol. The data so obtained are submitted in
TABLE IV-VAPOR PRESSURE O F MIXTURES O F ALCOHOL,ETHER, ___ .-66*/3% E7CAER; 33I/s% ALCOHOL
Wnter 100% 5.10 6.90 9.36 13.16 17.37 23, 66 32.18 42.38 55.37 71.87 92.71
Pure A 147.3 185.6 231.7 285.4 350.5 425.7 516.6 623.1 742.6 882.1 1041.3
95% A 148.6 186.8 233.8 288.3 353.1 429.7 521.7 628.3 749.9 891.8 1052.5
90% A 149.8 189.2 236.1 292.0 358.8 435.4 629.7 635.7 759,7 903.0 1066.0
85% A 152.0 192,s 239.3 295.0 362.8 442.6 536.6 645.4 771.4 916.1 1082.4
8O%A l&i.5 193.7 242.6 300.3 368.0 447.3 542.5 654.0 780.0 928.5, 1095.0
DATA
70% A 157.9 198.9 248.3 307.7 376.0 457.2 555.4 667.8 798.4 948.6 1120.0
60% A 165.4 207.0 259.4 319.9 392.3 476.0 577.0 695.2 829.0 984.0 1161.7
A N D WATER
173.6 217.3 269.2 332.2 407,6 494,5 600 4 721.8 861.0 1021.7 1206,4
__
--..33'/3,* 662/3'3
20% A 181.0 227.0 282.5 348.6 426 0 517.0 628.0 754.0 902.0 1069.0 1262.0
E
w
187.4 236.4 294.3 363.5 445.2 542.5 658.2 790.4 943.9 1120.6 1321.2
Pure ether 185.3 233.2 291.7 360.7 442.2 537.0 647.3 775.5 921.3 1089.8 1276.4
Pure alcohol 12.4 17.3 24.3 33.2 .44.4 59.7 79.3 103.1 134.6 173.3 221.1
TABLE V-VAPOR PRESSURES OF MIXTURES OF ALCOHOL,ETHER, A N D WATER Temgerature C. 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
- - -p- , p ,
PureA 152.8 191.6 240.5 294.9 361.7 440.6 534.7 643.2 767.6 911.4 1075.1
95% A 154.7 194.7 243.4 299.7 366.1 446.3 541.3 651.4 777.1 924.1 1092.0
90% A 157.4 197.3 246.5 303.5 370.2 452.8 547.1 659.4 789.0 935.9 1105.7
71.43% ETHER; 28.57% 85% A 80% A 161.2 160.0 200.6 199.8 251.2 248.8 305.7 308.5 378.7 374.2 462.2 457.3 660.2 553.6 665.7 673.2 804.4 796.3 945.8 955.8 1116.1 1128.8
ALCOHOL---------------70% A 60% A 164.2 167.1 204.8 210.7 261.6 2 5 5 , 3 315.5 323.0 395.6 387.1 481.9 473.2 585.6 573.6 704.9 690,3 838.5 823.4 998.0 977.0 1155.2 1178.5
40% A 174.5 218.2 272.2 386.3 412.0 501.1 606.7 729.6 870.0 1033.6 1220.5
20% A 181.8 227.2 283.3 350.2 428.7 521.0 631.5 757.4 903.4 1071.8 1264.3
71.43% E 28.57% W 189.3 236 1 295.6 364.4 446.7 543.2 658.7 791.8 944.6 1122.0 1322.3
Ether 185.3 233.2 291.7 360.7 442.2 537.0 647.3 775.5 921.3 1089.8 1276.4
September, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Tables I and 11, in which they have been compared with the values of Ramsay and Young. All determinations were carried out in duplicate and agreed within 1 mm. The vapor pressures of the various special systems were
935
then measured. The data appear in Tables I11 and VI, and have also been plotted in the form of pressure-temperature curves in the accompanying charts. All determinations were carried out in duplicate.
Note on the Hicks Method of Determining Potassium’” By R. C. Wells, R. K. Bailey, and J. G. Fairchild GEOLOGICAL SORVEV, D E P A R T M E N T OF THE INTERIOR, WASHINGTON, D. C.
HE modified chloroplatinate method of determining potassium in salts and brines described by Hicks3in 1913 has been used since that time for rapid survey work with generally satisfactory results. Occasionally, however, determinations on the same sample by different analysts would differ considerably, especially with percentages of t h e or.der of 1 per cent and under. This led the writers to make many experiments on the effe‘cts of slight modifications of procedure, the conclusions from which may be of general interest. It is unnecessary to repeat the full description of t h e method here. The purpose of this note is to emphasize certain precautions rather than to criticize the method. The direction to wash with alcohol “of a t least 80 per cent strength” suggests that 95 per cent or even absolute alcohol may be used, and the writers made a good many determinations with alcohol of these strengths. Blank tests and check determinations with known mixtures, however, show that a small excess of platinum is generally obtained with the stronger alcohol, which may range from a few tenths of a milligram to 4.0 mb. according to the care used. This was in the presence of about 0.5 gram of pure sodium chloride as the principal salt. I n most of the tests the filter papers were not drained by suction, but in other respects the Hicks procedure was carefully followed. The results led to the conclusion that each analyat should without fail make blank tests with salts similar to his unknown mixtures rather than rely too much on his ability to follow an outlined procedure. Working as uniformly as possible, corrections based on blank tests have been made occasionally when the results seemed of sufficient importance. Many tests, however, led to the belief that it is unwise t o count very strongly on the significance of the tentha of a milligram of platinum and the corresponding quantities of potassium. Geologists should also understand this and not attempt to make fine distinctions between reported percentages of potassiumin salt beds, brines, etc., when the method of analysis does not warrant it. This applies especially to very small percentages. The relative magnification of errors that fall entirely on a minor constituent, as in this case, suggests that for strictly accurate results with small percentages of potassium the great excess of other salts should be removed before an estimation of potassium is attempted. The persistent positive error referred to above seems to be caused in part by the enclosure of some platinum compound i n the sodium chloride. Dittmar and McArthur4 found a similar behavior with sodium sulfate. The results are also affected, however, by the strength of $he wash alcohol. Sufficient washing with alcohol of 80
T
1 2
a 4
Received Mav 10. 1924. Published by permission of the Director, U. S. Geological Survey.
’ ~ m sJOURNAL, 6 , 6 S O (1913). Trans. Roy. SOC.Edznbuugh, 33, 595 (1888).
per cent by weight will dissolve out several tenths of a gram of sodium chloride, and of course with it any enclosed excess of reagent. Further, although potassium chloroplatinate is almost insoluble in absolute alcohol, it becomes increasingly soluble in weaker alcohol. Thus, with weaker alcohol any positive error is both reduced and compensated by a negative error. The extent of compensation, however, will depend on the proportions of the different salts, the volume of wash alcohol, and to an even greater extent on the “personal equation” of the analyst. According to the writers’ experience 90 or 95 per cent alcohol should give better results with small percentages of potassium than either 80 per cent or absolute alcohol, but they feel that, in general, blank tests are a much better insurance against errors than reliance on definite specifications. The improvement resulting from a double evaporation with intervening decantation of the excess of reagent does not warrant the extra expenditure of time. Adding a t least 5 cc. of hydrochloric acid before beginning the evaporation is recommended, however. Also, it cannot be too strongly emphasized that the mixture of salts must be very thoroughly ground during the leaching with alcohol, and in washing chlorides out of the platinum a silver nitrate test should be required, as the platinum moss appears to retain a little chloride tenaciously. I n Table I are given some representative results that illustrate these tests. TABLEI (Figures are in grams) CONDITIONS OF NaCl Expt. EXPERIMGNT taken 13W Absolute alcohol 0.5000 58W 5 cc. HCl, absolute alcoho1,suction 0.5000 33W Absolute alcohol 0.5000 16W Absolute alcohol 0,2000 31W 5 cc. HCl, absolute alcohol 0,5000 60F 5 cc. HC1, absolute alcohol 0,5000 56W 5 cc. HCl, absolute alcohol suction 0,5000 27B 95 percent alcohol 0,5000 42F 95 per cent alcohol 0,2000 95 per cent alcohol 1.5000 33B 55W 5 cc. HC1, 80 Der c e n t alcohol, suction 0.6000 57W Same as preceding 0.5000 39aF 74 er cent alcohol &O per cent by volume) 0.5000 41F 74 per cent alcohol (80 per cent by volume) 0.6000 17W 74 per cent alcohol (80 per cent by volume) 0 2000 36aF 67 per cent alcohol 0,5000 24w Two evaporations, absolute alcohol 0 5000 36W T w o evaporations, absolute alcohol 0.5000
Theoretical
Error in Pt + O , 0009
KC1 taken None
Pt found 0.0009
None 0.0025 0.0500
0.0004 0.0038 0.0676
None 0.0033 0.0665
+0.0004 +0.0005
0.0025
0.0037
0.0033
$0.0004
0.0060. 0.0080
0.0079
+0.0001
0.0100 0.0160 0.0450 0.0112
0.0131 0.0221 0.0609 0.0166
0.0131 0.0209 0.0589 0.0147
None $0.0012
None
0.0002
None
+0.0002
0.0100
0.0108
0.0131
-0.0023
0.0140
0,0171
0,0183
-0,0012
0,0350
0.0442
0.0458
-0.0016
0.0500 0,0020
0 0662 0,0010
0 0655 0.0026
+0.0007 0.0016
0,0037
0.0057
0.0049
$0. 0008
0,0250
0.0324
0.0328
- 0.0004
Pi None
+0.0021
+0.0020
+0.0019
-
