VAPOR-PRESSURE RELATIONS I N TWO LIQUIDS, I1
MIXTURES O F
BY A. ERNEST TAPLOR
In the previous part of this article, the methods of determini n g vapor-pressures and boiling-points have been discussed in detail. T h e next thing to consider is naturally the numerical results obtained with the use of t h e apparatus described. T h e present paper will concern itself almost solely with a recording of the data which I observed, first with regard to t h e vaporpressures of solutions of acetone and water at various temperatures, and secondly with regard to the composition of the vapor given off under similar conditions. T h e first set of measurements are given in Tables I-XIII, the second in Table XIV. T h e tables do not contain carefully selected data, but they record the measurements as actually made in the series. A few of the first sets have been discarded, and possibly half a dozen individual measurements have been omitted which evidently contained large errors in reading. I t will be noted that at low temperatures the temperature rises rapidly with the pressure. These measurements were in consequence very hard to make, and probably contain a much greater error than the average measurements. T h e greater the percentage of water the greater is the change of the temperature with the change of pressure. T h e ten and twenty percent acetone solutions were therefore much more difficult to measure than the rest, and their vapor-pressure relations must assuredly be less accurately determined than those of the solutions richer in acetone. Whenever with slight increase of pressure the temperature rises rapidly, it is almost impossible to make very accurate
, I
356
A. Ernest Taylop.
measurements, T h e reason for this is, that it is so very difficult to keep the temperatnre constant for any length of time. T o make accurate readings it is necessary that the temperature should remain essentially unchanged for ten or fifteen minutes, for equilibrium cannot be established much sooner. Any slight leak will raise the boiling-point and perhaps make it necessary to raise the temperature of the bath, which will also i n turn raise the pressure and consequently the boiling-point. This then explains very completely why some rather large discrepancies are to be noticed at the lower temperatures and i n those solutions containing a very large percent of water. Table I contains the measurements made of the vaporpressure of pure water. I n the table they are compared with those of Regnault recalculated by Broch' as found in Landolt and Bornstein's Tabellen. T h e agreement is fairly good and is easily within my experimental error. In my further work I have used the figures of Regnault, as being measured much more accurately than was possible with m y apparatus. Tables 11-X contain my measurements with aqueous acetone solutions varyi n g from ten to ninety percent by weight of acetone. Table X I contains similar measurements with pure acetone and at the end the measurements of Regnault. At the lower temperatures my measurements agree well with those of Regnault, but at high temperatures there is a greater discrepancy. These measurements with pure acetone are not difficult to make, and in subsequent work I have preferred to use my own measurements. T h e measurements recorded i n Tables I-XI were plotted on a large scale as a temperature-pressure diagram, the temperatures being measured along the abscissa and the pressures along the ordinate. Each tenth of a degree corresponded to one millimeter and each millimeter pressure to half a millimeter on the diagram. Fig. I represents this diagram on a small scale. Through the points thus plotted, i t was found possible to pass smooth curves for the various solutions. Most of the points lay well on the curves, but i n some few cases a much greater error than is desirable came in. Trav. et Mem. du Bur. internat. des Poid et Mes.
IA, p.
33' 1881.
Vapor-$ressure Relations
z'iz
Mixiures of Two Liquids 357
T h e curve at the bottom of the diagram is that for pure water, the next that for ten percent acetone, the next twenty percent, and so on, the highest curve being that for pure acetone. It will be noticed that the pitch of the acetone curve is very much greater than that of the water curve, and that the change from one to the other is made gradually through the various solutions. At low temperatures the curves come very close together and spread out rapidly a t higher temperatures. At any one fixed temperature the effect of adding a little acetone to the water is very noticeable in the rapid rise of the pressure, as for instance i n going from pure water to ten percent and then to twenty percent acetone. After thirty percent, the rise in pressure is comparatively small. In the same way starting from pure acetone the fall in pressure to ninety percent is much greater than that from ninety to eighty. These two effects from the water end and from the acetone end meet somewhere a t about sixty percent, the change in pressure from fifty to sixty percent acetone and from sixty to seventy percent acetone being the smallest. These curves were extended somewhat beyond the actual readings made, so that they all go to 800 mm pressure and as low as 25' C temperature. From the curves in Fig. I , the data in Table XI1 was compiled. This table contains the temperatures obtaining at constant pressures, which range from IOO mm to 800 mm for the various solutions. T h e vertical columns have for headings the percentage acetone composition of the solutions, and the horizontal ones the constant pressures. This table, as it is taken from the curves in Fig. I , should represent a careful averaging of all the data given in Tables I-XI. T h e data from Table XI1 has been plotted as a series of constant pressure curves i n Fig. 2. T h e temperatures are measured as abscissae and the percentage concentrations of acetone as ordinates. T h e curve at the left is that for 150 mm pressure, the next for 2 0 0 mm pressure and so on u p to 800 m m pressure. They form a series of very nearly parallel curves of rather peculiar shape. I n the middle portion they approach
S
O
Fig
I.
Vapor-#ressure Relations
80'
3 0 '
~
40"
SO"
it2
iWixtuves of Two Liquids 359
60' Fig.
70"
80"
yo"
/oOd
2
very nearly to straight lines, but a t the acetone and a t the water ends there is a very decided change in the pitch of the curves. Table XI11 is a compiling from the curves in Fig. I of the pressures which obtain a t constant temperatures. T h e data from this table is graphically expressed in a concentration-pressure diagram in Fig. 3. T h e concentrations are measured as abscissz and the pressures as ordinates. T h e lowest ciirve represents the
360
A. Ernest Taylor
Fig. 3
pressure and concentration relations which exist at 25" C, the next curve represents similar relations a t 30' C and so on by intervals of five degrees up to 60" C. These curves start very close together at the pure water line, the pressures rapidly rising with increase of acetone, then more slowly, and from about sixtyfive percent acetone again more rapidly, the curve radically changing its form at this point. T h e next thing to consider is the composition of the vapor given off from the various solutions. As previously described, 2 2 0 cc of solution was taken each time and 2 0 cc distilled over, and its composition determined from its boiling-point. I t was found that the vapor composition varied but little with the change in pressure, so each solution was distillled at but two different pressures, viz. atmospheric and a t 200-250 mm pressure. T h e results obtained are given i n Table XIV. I n the first column A are given the percentage compositions of the so-
TABLEI Water I
'
Press mm
i
B Pt
23.0
23.5 25.5 27.5 34.5 38.5 40.5 42.5 44 46
22.1
i
23.8 25.4
1
49.5 66 70 74.5
,
33.2 1 36.2
17.36 19.63 22.15 24.96 28.06 31.51 35.32 41.78
37.2
i
20.0
1
22.0
24.0 26.0 28.0 30.0
32.0 35.0
Press
98 107
116 Regr 49.26 , 54.86 61.02 71.36 83.19 91.98 101.55 1 117.52 ~
B Pt
128.5 I43 I45 146 I74 173.5 198.j 200.5 226.5 226.5 251 252 276 278 300
302
342.5
BPt
38.7" 43.4 44.7 46.0 48.6 49.4 50.2 51.5 52.4 52.8 53.2 54.9 ult 38.0 40.0 42.0 45.0 48..0 50.0 52.0 55.0
Press mm
Inm
38.2' 344.5 40.7 396.5 40.9 446 41.1 506 507.5 44.5 44.6 543.0 47.5 I 600.5 47.7 596.5 50.6 1 652 50.6 652 52.9 697.5 53.0 695.5 695.5 55.0
1
1
'
Press mm
,
20.8'
19.? 20.5
1
Press mm
117.5 124.5 I 28.5 135.5 141.5 146.5 149.5 158.5 161.0 164.5 195.7, 200.5
135.57 148.88 163.29 187.I O 213.79 233.31 254.30 288.76 TABLE I1 10% Acetone
i1
B Pt
_55.0' 56.5 57.1 58.2 59.1 59.9 60.3 61.3 61.9 62.2 66.0 66.55 58.0
60.0 62.0 65.0 68 o 70.0 72.0
75.0
Press mm
B Pt
-
203.5 238 242.5 287 289 355 357 365.5 438.5 4403 5 517.5 540.5 631.5 327.05 354.87 384.64 433.19 486.76 525.47 566.71 633.66
67.1' 70.4 71.0 74.9 75- 1
80.0
80.3 80.8
85.4 85.5 89.85 90.75 94.85 78.0 80.0 82.0
85.0
88.0 90.0 92.0 95.0
B Pt
Press mm
B Pt
Press mm
B Pt
60.4' 63.55 66.6
I43 I45 745 I47 181 183 186.5
40.4' 41.0
295.5 348 352 404
56.6' 60.8 60.9 64.3 64.3 67. I 67. I 69. I 69.3 71.6 73.6
41.1
41.3 45.5 46.0 46.2 74.3 , 74.1 200 47.7 202 48.0 76. 3 76.2 50.9 231 51.1 78.3 233 78.05 262.5 54.2 258.5 53.5 77.9 80.0 258.5 53.6 278.5 55.3 79.8 - 282 - 295.5 55.5 56.6 70.0
70.2 72.0
305
452.5 153.5 497.5 499 5.51
I
595.5 597.5 650 695.5 695.5 742 742
73.8
76. I 78.5 78.4 80.05 79.9
A. Ernest Taylor
362
TABLEI11 20
__
-
B Pt
Press mm
-27.2'
117
I 26
29.5 128 29.8 140.5 31.7 141.5 31.9 I44 32.4 I47 32.7 173.5 36.2 177.5 36.6 198.5 39.2 253 44.5 257 44.7 295 48.0 296 48.0 354 5 2 . 2 356 52.4 357 5 2 . 5 395.5 54.9 446 57.7 417 57.9
Press mm
B Pt
% Acetone __
Press mm
--
-_.
497.5 498.5 542.5 542.5 598.5 598.5 636 646 647 692.5 693 7 30.5 121.5 127.5 131.5 '33.5 136 159.5
60.7" 60.8 63.0 62.9 65.55 65.6
BPt
Press mm
--
-_.
644 645 712
716 743.7 1.59.: 163 164 196.5 198.5 198.5
67. I
67.55 67.65 69.4 69.4 70.7 28. I 448 29. I 149.5 30.2 498.5 30.6 499.5 30.9 548.5 549.5 598.5 598.5
34.1 34.7 35.0 38.6
38.7 38.75 225 40.5 249 43.8 247.5 43.7 274 46. I 275.5 46.2
57.9 58.0 60.7 60.7 63.0 302 63- 0 5 303 65.2 344 65.25 $00
48.2
48.3 51.5 55.0
TABLEI V 30% Acetone Press mm
B Pt I
i
Press mm
178.5
27.9" I 302 29.1 303 29.6 I 351.5 31.7 I 346.5
178.5
31.8
187.5 191.5 196.j 243 245 251 253
32.8 337 33.4 1 402.5 33.8 403.5 38.9 449.0 39.1 451.5 39.5 j 39.6 -
148.5
I j6.6 161.j
B Pt
453.5 501.5
53.6' 698 56.2 737 56.2 58.6 61.2 1 61.2 1 61.25 1 63.2 63.3 65.3 I -
43.7" 43.7 47.2
j02.5
I
46.95 45.95 46.3 50.6 50.6 53.4 53.55
549.5 601.0 602 603
~
,
I
-
Press 1 B Pt nini j
Bt Pt
1
333
'
Press mm
6 jo
65 1 700.5
~
~
~
~
Vajov-pvessuve ReZations i i z Mixtuves of Two L i p i d s 363
TABLE V 40% Acetone Press
mm
._-
I 27.6' 176 I 86 28.8 191.5 29.6 344.5 43.6 348.5 43.8 451.5 50.3 55.0 538 540 55.3 639 59.9 60.0 643
734.8 I57 165.5 176.0 I 80.5 183 184 193.5 I99 245
~
306.5 307.5 351.5 353.5 404.5 406 448.5 449.5 524.5 527
63.7' 25.6 26.6 28. I 28.6 28.8 29. I 30.2 30.8 35.7
40.7O 40.8j 44.2 44.3 47.7 47.75
544 596 599 645.5 646.5 690.5
54.65 , 738.5 55.45 I -
55.50 57.9 58.0 60.3 60.3 62.2 62.25 63. I 63.05 63.8
-
TABLE VI 50 % Acetone I
I
1 I
204.5 212.5
315 318 316.5 437 441
~
29.2 30.3
526.5 627.5
1 52.7 1 203.5 1
, 39.6 1 146.5 I I 39.7
I 39.7 1 47.9 I 48.0
1
1
152.5 157.5 161.5 169.0
Press mm
57.7
205.5
22.1
314.0 349 401.5 406 449.5
22.8 23.6 24. I 25.2
B Pt
25.7" 26. I 29.3 29.4 34.3 34.6 39.4 39.6 42.2 45.8 46.0 48.8
' '
Press mm
B P ~
496.5 51.3 498 1 51.4 548 1 53.9 597 , 56.2 648 58.5 647.5 1 58.45 693 1 60.5 745.3 1 62.5
-I--1-
- -
A. Emzest TayZo??
364
TABI,E VI1 60 $% Acetone B Pt
1'
I
Press mm
I1
I
B Pt
I
Press mm
453 206.5 209.5 297.5 299.5 301.5 397.5 399.5
1 27.8 I
,
502
504
1
625 735.5 156.5 159.5 161 I 65 I 68 198.5 200.5
28.1 36.8 36.9 37.0 43.9 44.0
50.2 50.2
56.2 60.85 21.6
244.6 246 297.5
22. I
300
22.5 23.0 22.4
36.7 36.9 40.9 40.9 43.9 44.0 47.2
351 352 396 398 450
27.0
27.35
500 550.5 550.5 607 642.5 643.5 696.5 701.5 739
32. I 32.2
-
1 1
BPt
-
1.47.4O
I 52.65 50*1
I 52.7 ~
~
1 -
55.3 56.9 57.0 59.2 59.4 61.0
TABLE VI11 70 % Acetone
_I-
Press mm
~
B Pt
I
I
I
B P ~1
Press mm ~
196.5 208.5 215.5 228.5 257.0 2 60 298 298.5 301 * 5 395 399 502.5
I
Press mnl
25.9' 27.0
,
'1
27.9 592.5 595 29.4 32.2 674 1 32.4 680 684 35.7 35.8 729.5 36.0 163.5 177.5 42.9 43.1 1 181 1 49.2 1 186.5 1
53.7 I 216.5 53.8 I 222.5 251.5 57.5 57.7 254.5 305 59.7 307 5 21. 7 351.5 354.7 24.1 400 24.7 404.5 9
I
B Pt ~
Press mni
-- l_- l
458.5 459.5 28.1 504.5 28.85 506.5 31.7 555 32.0 1 556 36.25 602 36.5 604 39.95 649.5 40.2 695 43.3 I 696 43.5 748.5 ~
II
1
B Pt
46.8' 46.95 49.3 49.4 51.95 52.0 54.1 54.2 56.2 58. I
I 58.1 I 60.3
TABLE IX 80% Acetone I
mm
1
nlnl
Press ni m
1
B Pt
Press
--____.
59.0' 21.6 22.1
1 25.2 253 30.9 262 31.6 268 32.2 299 34.8 302 35.1 307 I 35.4 355 1 39.0 357.5 I 39.2 359 39.4 398 41.9 403 42.3 200
~
1
~
~
1 I
I I ~
I
1
499.5 502.5 548.5 550.5 1 552.5 I 596.5 599.5 644.5 1 647.5 1 ~
22.3 24.4 24.5
48.0 48.2 50.6 50.7 50.75 52.8 53.0 55.0 55.1
B Pt
inn] I
27.5
1 ,
1
30.6 I 33.3
405 407.5 456 5 458.5
42.40
42.6 45.6
45.7 510.5 48.6 513 148.8 516.5 148.9 551.5 50.7 50.8
53.3 55.2 56.9
58.9
-
TABLE X 90%
213.5 214 216 255 254 263 305.5 308.5 311 346
25.7 25.6 25.8 29.8 29.6 30.5 34.1 34.3 34.4
3 50
37.45 40.6 40.7 44.4
396 398 458.5
Acetoile
57.7
37.35 - 1
- 1
-
-
- -
A . Ernest Taylor
366
TABLE XI Acetone
'
-.
Press mm
188.5
192.5 194.5 I95 I97 218 222
254.5 261.5 295 30 1 308 345 179.6 281.0
B Pt
Press mm
-.
B Pt
--
---
' 347
35.2O 348 35.3 21.3 397.5 38.5 21.45 399.5 38.7 21.7 403.5 39.1 23.9 498 44.6 24-3 506 44.9 27.6 507.5 45.0 28.2 548 * 5 47.2 31.2 554.5 47.5 31.7 593.5 49.4 32.3 596.5 49.5 51.7 35.0 645 Reg ault 20.0 420. I 40.0 620.9 50.0 30.0 20.7 21.1
Press mm
647 603 615 640.5 642.5 695.5 697.5 697.5 737.5 318 353.5 355.5 397 I
860.5 189.4
1
B Pt
I
Press
B Pt
_-
35.7 35.9 38.7
739.5
-
38.8' 41.7 44.7 47.2 47.3 49.8 49.8 52.0 54.1 54.2 55.7
.
Va#or-jressure Relations i i z Mixtures of Two Liquids 367 TABLE XI11 Pressures ( At
% Ac
'
60'
I
55'
constant temperature)
soo
mm
mm
1
149 117.5 92 221 339 275 324 485 399
70
1
80
1
740 774
o 10
1
20
go
808
621 645 680
~
I
45O mm
71.5 I77 262
5'7.5 428 536 447 566.5 469
lutions before distilling, in column AI the average composition of the solution during distillation. This is the average of the composition of the solution a t the beginning and at the end of the distillation. Column V gives the percentage acetone composition of the vapor given off, and Vr the composition of the vapor which would be given off by the original solution if its composition did not change. T h e results are obtained by plotting the original data and interpolating. I n column P are given the pressures under which the distillations took place. (Atm is an abbreviation for atmospheric pressure, that being a t this time about 740 mm). In column M are given the vapor compositions in molecular concentrations. They exactly correspond to column VI. These molecular concentrations represent the number of molecular weights of acetone in one hundred molecular weights of vapor. T h e first thing which one notices in looking over this table is the large percentage of acetone given off in the vapor even of the ten percent solution. This makes the measurements difficult. As will be seen, in boiling off 2 0 cc of condensed vapor from 2 2 0 cc of I O percent acetone solution, the composition of the solution changes from ten percent to three and a half percent.
A. Eovizest TayZoov
368
There is sure to be introduced a considerable error, when the composition changes so markedly during distillation. T h i s does not come in much with the higher concentrations, for while the
TABLG XIV
,I
A
I
I
A,
I
IO IO 20 20
1 1
I 1
30 30
40 40 50 50 60 60 70 70 80
80 90 90
'
6.8 6.9 16.6 16.7 26.9 27 37.3 37.45 47.75 47.85 58.25 58.35 68.7 68.8 79.15 79.25 89.65 89.7
74 72.5 88
85.5 92.5 90
93~5 9' 95.3 93 94.5 93.5 95.5 94.3 97.3 95.5
~
i
I
81
2 00
78
atm
89.8 87.3 93 90.5 93.8 91.3 95.3 93 94.5 93.8 95.8 94.5 97.3 95.5
200
atrn 200
atm 200
atm 225 atni 250 atm 250 atm 250 atm
57 52.5 73 68 So. 5 74.8 82.3 76.3 86.3 80. j
84.3 82.3 87.5
84.3 91.8 86.8 91.8 88.3
twenty percent solution gives off a ninety percent vapor, the ninety percent solution gives off only a ninety-seven percent vapor. With change of pressure - t h e composition does not change greatly, on the average about two percent for 500 mm change in pressure. T h e vapor compositions are given to the quarter percents, and are accurate to about one percent, although in some cases there may be as great an error as two percent. T h e boiling-point method of determining composition is not especially accurate. T h i s with the great difference i n composition of the vapor and liquid makes an accuracy of one percent about all that can be hoped for. On looking a t column M, however, it will be seen that a n error of one percent i n V,will introduce a greater error in M. T h i s is due to the great difference in the molecular
Vajov-fivessuve Relal'ions in Mixluves of T w o Liquids 369 weights of water and acetone, viz. 18-58. T h e partial pressure of the acetone in the vapor, of course, depends upon the relative number of molecular weights of acetone found in the vapor. T h e numerical results will soon be followed by a theoretical consideration of the same. Cornell Universify .
