260
'
E. ABEL
Aluminum sulfate solutions have surface tensions that are exceptionally high when compared with those of other inorganic salts on a molal concentration basis. The effectiveness of a number of compounds in this respect is approximately proportional to the total ionic charge of the molecule. REFERENCES (1) ADAM,N.
IC,: The Physics and Chemistry of Surfaces, 3rd edition, p. 374. Oxford Uni-
versity Press, London (1941). C. D. (Editor): Handbook of Chemistry and Physics, 23rd edition, pp. 1144, (2) HODGMAN, 1320, 1321. Chemical Rabber Publishing Company, Cleveland, Ohio (1939). (3) SENTIS,M. H.: See Intevnational Critical Tables, Vol. IV, p. 465. McGraw-Hill Book Company, Inc., New York (1928).
.
T H E VAPOR PHASE ABOVE T H E SYSTEM SULFURIC ACID-WATER E. ABEL 68, Hamilton Terrace, London, N . W . 8 , England Received J u n e 18, 1046 I. THERMODYNAMIC RELATIONSHIPS
The value of the vapor pressure (p,) of HzSOdl above the liquid system sulfuric acid-water with T weight per cent Hi304 is such that its molal free energy of formation' (AG,(g)) is equal to the partialmolal free energy of formation (AG,) of the liquid component HzSOd(a) a t the same temperature, T. If a, is the activity of the.latter, then AG,(g) = AG, = AG'(g) R T l n p , = A@ RTIna,
+
+
AG'(g) is connected with the standard free energies of formation of HzO(g) and S03(g) by the dissociation constant, K,, of H2S0d(g):
Therefore, ) RTln K , RTlnp, = A G ~ -
+ RTlna,
where AG(0) is the free energy of formation of (H2S04)0from HzO'(g) and SO",g) : HzO'(g)
+ SO:(g)
= (HzS04)'; AG(')7 AH('), As('), AcC)
1 The sulfuric acid Component, HZS04(?r) ; the water component, HtO(r); the gas state, (g). Standard states are designated by a superscript cipher: sulfuric acid in its standard state, (HzS04)0. Values relating to water or sulfur trioxide take the index w or u. Absence of an index indicates values relating to sulfuric acid. 7 = 298°K. Values for 0°K. take a left-hand top indexo. As we are dealing with a binary liquid system, all thermodynamic quantities are, of course, partial molal quantities; for the sake of simplicity the bar is omitted. 2 The vapors are treated as ideal gases; see references 12a, 13,74,126:
261
VAPOR PHASE ABOVE SULFURIC ACID-WATER SYSTEM
For the formation of H2S04(?r)from the same components we have similarly: HzOo(g)
+
=
HzS04(n); A G ( d , AH(r), AC(r)
With dAG(O)/T - -AH(o) = dT T2
AH'(O)
+ ST AC(O)-dT T2 rT
we get
Putting AC(T) = A0C(n)
+ Aa(?r)*T
then
+
- ~ c ' ( ? r ) (A'c(T)
+ ~a'(a).r)k+ AOC(~)In -T + 7
A~'(~).T
(Aa'(?r) = i A a ( ~ ) )
Finally, writing 1%
Pr
A,
+ B, + Dr log T + E,T
expressed in mm. Hg (additional term: log K
p
= k1
A,
+ f(T)
+ 2 log 760), then, putting (10)
+ + ks log T + k4T ib2
= 5.88 -
5T000 + 1.75log T - 5.7 X lo4
the coefficients of the vapor pressure formula for H2S04 above an aqueous solution of sulfuric acid with ?r weight per cent H2S04 are: A,=A+loga',+--,
R
[--L'r + 2.30AuC(?r).logr+ A e ( r ) ] = A + A:
(R* = 4.58R)
* L , is the relative partial niolal heat content of €12S04(?r)relative to 4
The values relating to T = 0 are, of course, purely fictive.
(HzS04)0.
262
E. ABEL
where
is a constant independent of concentration and temperature:
11. NUMERICAL RELATIONSHIPS
A . The constant A Table 1contains the thermodynamic data from which the entropy of formation (Ax'(O)) of (H~804)'from HzO'(g) and SO:(g) at T = 298" can be calculated. There is, according to the values used, a certain latitude in A,S"(O), so that from the data at present available its value is not defined closer than As'(') = - 96.3 f 7.7 E.U.
Therefore
A = 20.95 f 1.65 (If the most recent value, A,Go = -88.5 kg-cal., is used, A would be 21.7 =t 0.4.)
B. The actiuities, a , The activity of sulfuric acid has been determined by many authors (1, 23, 31, 37,40,42,44,48,51,63,64,66,88,89,91,93,96, 102a, 102b, 106, 107a, 107b, 108b, 125, 127), particularly by measurements of E . M . F . ~of suitable cells; their widest v n g e (up to a = 63.2) and their most accurate values as well are due to Harned and Hamer (43). At present, the only possible way of obtaining activity values beyond this range seems to be t o use the water vapor pressures wp,,according t o the thermodynamic relationship
where ,v, is the number of moles of HzO for 1mole of H2S04 in HzS04(a). Table 2 shows in column 2 the water vapor pressures a t 25°C. for a P 50, based on a critical examination of thevery extensive material (7,12b, 13, 15, 18, 21, 22,24b, 27, 32, 35, 37, 38, 40, 43, 46b, 49, 56, 58, 62, 65a, 66, 67, 70, 75, 78, 79, 88, 94b, 97, 102, 104, 105, 109, 110, 112, 117, 120, 121, 128, 129) on the total vapor pressures of aqueous sulfuric acid; within a wide range of temperature and concentration
VAPOR PHASE ABOVE SULFURIC ACID-WATER SYSTEM
4 4 3
2
v)
263
264
E. ABEL
these are, of course, identical with the water vapor pressures wp. The logarithms of the activities and the activity coefficients so obtained are shown in the same table (columns 3 and 4), in comparison with the values of Harned and €hmer (columns 5 and 6). The series of values fit together well, as figure 1 shows. e
C . The relative partial molal heat contents, L', (table 3) Within a wide range the well-known methods for evaluating partial molal quantities (64, 90, 98) could be avoided as, up to 7~ = 60, the relative partial molal heat contents L', have been obtained by Harned and Hamer (43) from TABLE 2 The activity of H2SOa(a)
25°C.
This paper
Harned and Hamer log a,
WQI
mm. Hg
10 20 30 40 50 55 60 63.2 65 70 75 80 85 90 95 (8)
8.40 6.17 4.00
I
I . 553 '
2.25 0.99 0.44 0.14 0.039 0.00765 0.00060(")
L .306
0.77 1.13
i.140 it995 i.775 ' .543 1.207 I . 779 1.225
1.72 2.64 3.73 5.05 5.93 5.80 3.86
-1.924 -0.831 10.325 1.615 2.872 3.565 4.344 4.837
0.127 0.130 0.135 0.320 0.560 0.780 1.155 1.473
-3.12 -2.19 -1.44 -0.28 k0.63 1.68 0.00
3.01 1.13 4.17 4.75 5.26 5.68
2.11 2.71 3.,15 3.55
0.22 0.81 1.22 1.61
-3.58 -3.19
See Appendix, table 14.
the variation of the activities with temperature.6 The values for ?r > 60 have been calculated from the heats of mixing, M,, and the relative partial molal heat contents, wL:, of the water component.' 6 The same method was used by Cowperthwaite and Shrawder (20a) to determine L, for greatly diluted sulfuric acid (T between about 0.01 and 0.2). 6 I n the range in which the total vapor pressure is practically identical with the water vapor pressure, the heat of evaporation ,A, has been calculated from its variation with temperature, and from this and the heat of evaporation of pure water (,A), the relative partial molal heat content ,L, of H ~ O ( T ) , From these figures and the heats of mixing (relative t o 1mole of H2S04(1); M, = L, s ~ r w L -l 20.9 kg.-cal.) a t first approximate values of L,were obtained, with the help of which a n appropriate extension of Harned and Hamer's L+curve could be carried out. -Owing t o the war the author had access to the paper by Craig and Vinal (20b) only after completion of the manuscript.
+
\
VAPOR PHASE ABOVE SULFURIC ACID-WATER
SYSTEM
265
D. The partial molal heat capacities, C,, and their temperature coeficients We owe the most accurate determinations of the partial molal heat capacities of the components sulfuric acid and water to a recent paper of great precision by Randall and Taylor (92), but unfortunately their experiments were limited to a range of concentration up to .rr = 19 and to but one temperature, 25°C. To
6
1
+7
5-
k
+ t
"1
3
?r 2
+/
I
-3L FIG.1. Activity a', and activity coefficient f:
obtain a wider survey, therefore, we are confined to the use of determinations which were not originally intended to yield partial values. Among the many determinations (see 6b, 8, 9, 16, 19, 25,45,56, 69,77, 81,83,103,116, 122, 123, 134) of the specific heat of sulfuric acid of various concentrations, only those of Biron (6b) (room,temperature; in the following related to 18OC.) and to some extent of Ssokolik-Savaritzky (116) (22.5", 40" 60", 80°C.) can be used for our purpose7; only these are spaced closely enough to allow the partial molal heat capacities to be arrived at with some degree of accuracy. 7 See reference 64; the values entered in table 4 are calculated directly from Biron's figures.
266
E. ABEL TABLE 3
,J:, :Lr,i n kilogram-calories per
Relative partial molal heat content, L:, (2) 180
-&
0 0.47(0) 10 20 30 40 50 60 70 75 80 85 90 95 100 (a)
(b)
mole
(3)
(s,b)
~
~
w
(5) (
0
0
- L.
1
20.9 4.93(e) 5.60 6.05 8.10 10.0 12.1 14.4 17.0 18.0 19.0 19.8 20.5 20.8 20.9
17.3 17 .O 16.2 15.2 14.0 12.3 10.5 8.25 6.50 4.45 2.25
0.90 1.65 2.85 3.60 4.55 5.65 6.65 7.70 (8.80) (I)
0.60 0.90 2.20' 0.25 -0.20 2.45 8.75 6.45 (1.95) (f)
See references 13, 29,41,47,60b, 82,84,85, 86, lola, 101b, 122, 124. A. W. Porter (85) uses the formula (15OC.), expressed in our terminology,
+
40.34(5.44cp 1) 5 . 4 4 ~f 1.894
- 21.3;
q =
100 - 7T ?r
which fits well with the above data. See also reference 124. ( 0 ) See also International Critical Tables, Vol. V, p. 212. It should be noted that the value for - H ( r = 84.5;2OoC.) isprobab1yanerror;the figureshould be822.30andnot 830.68. (d) R . A. Morgan's determinations (73) (18°C.) of the partial molal heats of solution of liquid sulfur trioxide in water relative t o liquid SOs(.L,) do not agree with the partial molal heat contents of sulfuric acid in its aqueous solutions (Harned and Hamer (43)) from HtO(1) = H2SO4(1); which they can be calculated with the aid of the reaction SOa(1) aH = - 21.2 kg-cal. (Roth (99; see also 24a, 71)). As .L, = -21.2 - 20.9 L , - ,L, we get:
+
+
7r
-&
a
-&
10 20
36.5 35.4 34.6 33.7
40 50 60
31.6 29.1 26.0
25
30
(e) The heats of dilution and the relative partial molal heat contents of greatly diluted solutions of sulfuric acid were measured by Lange, Monheim, and Robinson (59) ; compare, on the other hand, reference 20a. (f) Est'rapolated.
VAPOR PHASE ABOVE SULFURIC ACID-WATER
2G7
SYSTEM
To determine their temperature coefficients, aI,for H2S04(a)and Pa for HzO(a), a t present only the above-mentioned measurements of Ssokolik-Savaritzky (116) can be used and even these only with certain reservations.' TABLE 4(b)
-(1)
(2)
(3)
;c ---R
(4)
c;
0 -1.5 -67.43(": 10 27.4 -8.7 f22.0 1525.6 -11.3 24.8 23.6 2024.6 -13.6 2525.0 -6.1 24.6 3018.4 -4.2 18.1 16.9 3517.0 -1.4 4013.9 +1.5 14.0 4516.2 f 2 . 6 16.7 5021.4 +4.7 21.6 5524.2 $3.7 24.5 6030.1 $5.0 30.6 6529.5 +8.0 30.1 70 34.6 flO.0 35.3 7538.2 +2.0 38.3 42.1 8042.2 -1.3 35.1 8535.4 -3.7 9029.4 +5.3 29.8 9531.6 +3.5 31.8 10033.0 f 3 . 4 33.2
(5)
(6)
'Cc. A C r ( r ) ----___
-62.9 -91.0 k47.9 -1.6 57.4 $1.2 0.0 61.8 42.8 f l . 0 30.6 -5.5 21.1 -6.7 9.5 -9.6 9.0 -6.9 7.6 -2.0 13.5 4-0.9 15.7 f 7 . 0 6 . 3 $6.5 5.5 +11.7 32.4f14.7 46.0 +18.5 46.1 $11.5 14.0 +6.2 21.3 $8.2 23.1 +9.6
(7)
-_ _
(8)
(9)
?&!Aoc(?r)"C;, -1.9 -85.3 -9.1 +25.5 -11.7 f36.1 -14.0 $41.8 -6.5f20.4 -4.6 $8.2 -1.8 -1.3 4-1.1 -12.9 f2.2 -13.5 4-4.3 -14.7 4-3.3 -8.9 f 4 . 6 -6.7 $7.6 -16.2 f 9 . 6 -16.9 +1.6 +9.9 -1.7 f23.6 -4.1 $23.7 $4.9 -8.4 $3.1 -1.0 f 3 . 0 $0.7
17.6 16.9 16.3 15.4 13.7 11.8 9.5 15.6 22.3 17.5 (7.3:
(10) I%
x
(11)
wc:
(12)
2,
101 --
-
+0.4 $1.1 $0.6 -0.1 -1.4 $3.5 $5.1 $5.8 -2.0 f2.6 f8.6)
+16.4 $8.0 $13.7 f5.3 f14.5 $6.1 f15.7 1 $7.3 $17.8 3-9.4 -6.9 $1.5 -5.4 -13.8 -1.4 -9.8 f28.0 f19.6 $9.9 f1.5 (-17.9: (-26.3)
17.6 17.0 16.3 15.4 13.6 12.0 9.9 16.0 22.2 17.7 (7.9)
~
(n) It should be noted that, of course, the values for ?r = 0 (90,98) do not enter into the formula for p r . (b) For columns 9-13 see Appendis.
By evaluating these determinations carefully, first the partial molal heat capacitiesg of HzSOd(.rr) for '7 and 0°K. were obtained (table 4, columns 4 and 5 ) , and then from this and the heat capacities of HzO(g)" and SOa(g)" the co8 In any case, the author thinks he has obtained values as reliable as the present experimental determinations allow. See last remark in footnote 6. 9 The relative partial molal heat capacities (25°C.; relative to ?r = 0) of the HzSOIcomponent are deduced by Harned and Hamer (43) from electromotive measurements, but "they do not give much weight to their accuracy, since these values involve the second differential coefficient of the original electromotive forces." Furthermore, according to the recent measurements of Randall and Taylor (92), the authors have not been able to obtain the value for infinite dilution between the range of their measurements, 10 From reference 64: ,C(g) = 8.81 - 1.9 X 10-ST 2.22 X 10-YP = 8.42 within the range of temperature under consideration; see also reference 29. 11 Tho molal heat capacity of SOa(g) has not been adequately established as yct. We accept Chernobaev's figures (17), writing
+
.C(g) = 14.0 f 4.1 X 1O-T
Sec slso references 11, 55, 64.
268
E. ABEL
efficients which give the variation of the heat of formation A H ( n ) with temperature ( A C T ( a ) (column 6 ) ; A 0 C ( n ) (column 8 ) ; A a ( n ) (column 7 ) ; calories per mole degree and calories per mole degree2).
E . The heat offormalion ( A H r ( n ) ) of H2S04(n)from HlO(g) and SO,(g) A H " ( a ) = A H o v r - A,"
+ L',
- A,"
=
(-G2.85 If: 0.25) l2 f
kg-tal.
TABLE 5 The cocJkicnls n j the fornruln Jnr //re suljioic acid unpnr pressicrc p , (See page 261 ; p n in mm. Hg) (3)
(6)
E,
A,
5
(fl.2) f25.4 f39.5 +46.4 +20.l +3.5 -8.7 -23.8 -24.1 -24.7 -16.9 -13.0 -25.0 -24.8 +9.2 +27.1, f25.7 -15.2 -5.4
in 15 20 25 30 35 40 45 50 55 GO 65
io
75 80 85 90
95 08.3 (Dl (:I)
(f21.2) f45.4, +59.5 f66.4 +40.1 +23.5 $11.3 -3.8 -4.1 -4.7 $3.1 f7.0 -5.0 -4.8 f29.2 +47.1 f46.7 +4.8
$14.6
x
103
7.55 8.30 8.64 8.66 7.85 7.06 6.50 5.84 5.66 5.56 5.59 5.60 5.00 4.86 5.62 5.98 5.54 4.19 4.44
-5.58 -14.60 -19.90 -22.70 -12.00 -5.88 -1.10 +4.73 4-5.03 f5.62 $2.71 f1.76 +6.38 f6.73 -6.73 -13.60 -13.65 $2.46 -1.25
$6.7 f10.5 4-13.3 +15.9 $7.7 $5.6 +2.5
4.48
-1.75
-2.6
-0.6 -1.8
-4.2 -3.0 -1.5 -7.7 -9.9 -1.2 f2.4 $5.0 -4.8 -2.8
See page 270.
p, The coefficients of the vapor-pressure formula for p , are given in table 5 . 111. T H E COEFFICIENTS O F T H E VAPOR-PRESSURE FORMULA FOR
IY. EXAMINATION O F T H E EXPERIMENTAL MATERIAL
Experimental material to test the above relationships is sparse, but they seem capable of opening the way to an insight into the vapor phase above sulfuric acid within a wide range of concentration and temperature. In the following an attempt is made t o see how far the constant A ( = log p , - f(T) - A*,) can be evaluated from the available measurements. 12 I3
See table 1. Scc! tltble 3.
VAPOR PHASE ABOVE SULFURIC ACID-WATER
269
SYSTEM
A . Experiments by Burt We owe to Burt (15) a series of excellent measurements extending partly into a range ( n > 91.0; table 6) in which the t,otal vapor pressure P , can no longer be identified with the water vapor pressure ,,,p,; from ( P , - wp,) p , and .p, can be calculated with the help of K,. Column 8 shows that the values of A are indeed within the range calculated theoretically. As this is, however, a determination by difference, and since there is unavoidable uncertainty in the values of column 3, these values can hardly claim to be more accurate than to the nearest whole number.14
B. Experiments by Thomas and Barker (120) Thomas and Barker are, as far as the writer knows-with the exception of a previous paper by Thomas and Ramsay (121),which was invalidated by an errorthe only authors who have taken separate measurements of the two components of the vapor phase. The use of their experiments for our purpose assumes, T
=
TABLE 6 95; pressures in m m . Hg
(2)
(4)
(5)
(6)
(7)
(8)
P
P-WP
.79
P
AT
A
0.1 0.2 0.4 0.8
5.4 10.1 17.2 29.0
14.77 14.90 14.98 15.08
20.22 20.35 20.43 20.53
"C.
36.5 54.0 79.3 113.0
200 210 220 230 (8)
31.0 43.7 61.7 83.2
5.5 10.3 17.6 29.8
Calculated from the vapor-pressure formula for ,p (see Appendix, table 14).
however, that their values-at least on the sulfuric acid component-relate to saturated vapor, whereas this does not always appear to have been the case for the water component. It seems, therefore, appropriate to take for ,p, the difference between the total pressure P , (Burt (15); Blake and Greenewalt (7)) and the sum of the HzS04 and SO3 pressures, where the latter has been obtained by an approximation method which presumes the knowledge of Furthermore, their figures need supplementing and correcting,-the former with regard to the dissociation of the sulfuric acid vapor, the latter with regard to an error in their calculations, inasmuch as they did not distinguish properly between HzS04 and HzO SO3. The data needed for evaluation of A from p , were interpolated from the figures of table 5. These rather lengthy calculations were carried out in all the experimental series of Thomas and Barker; however, we wish to discuss here only the values for n 5 95, as the HzS04 activity a , can a t present be evaluated only up to this compo~ition.'~The value of the constant A calculated from these experiments is within the expected range, and its average is A = 20.0 (table 7).
+
14
The logarithmic connection with pT should be noted See table 2.
270
E , ABEL
C . The azeotropic concentralion, ii The azeotropic concentration is a t ii = 98.3.'' Various values are given for the azeotropic boiling point (at 1 atm.)"; according to Lewis and' Randall (04) this is 32G"C. TAI3IiT;: 7 Pressures in m m .H g -
TT
I
Lo
wbn
A
P,
Lo
R
wPr
-_____ _ _ - _ _ ~ _ _ 183 78.00.5 197.5 116.9 1 . 3 80.25 216.5 233.1 2 . 1 230 306.33.6 1244.5414.8 5.3
PT
A
(19.83) 191 50.7 0.6 19.97 205 84.7 1.0 19.90 222 158.5 4 . 5 19.94 91.26242.5271.6 6.4 252.5385.3 11.3 19.94 258 444.7 13.6 Average ........., . , . , . 19.94 1262.51411.l]16.3
(1
1
Average ,.,
?r
io
LLPC
[
b.
A
_____________
180 200 215.5 232. 211.5 20'02 19.94 95'06 252 261 19.94 270 , , , . . ,. , . . 19.96 280.5 282 (19.63) 19.91 20.02 19.DO
13.4 2.4520.14 32.3 4.3520.05 60.0 8.2520.10 112 12.5 20.01 170 19.6 20.08 225 19.4 19.99 296 26.8 20.02 391 37.8 20.07 540 47.8 20.06 560 148.8 20.04
Average ... . . . . , . . . . ,
.
20.06
If a(g) is the weight per cent HzS04 in the vapor phase, then, for this boiling point (&), from the three equations: a(g) = ii =
p; p;
4- @;
+
+ up;
p; 80 -up; 98
-t
18
. 100
GlVp;
+ u p ; = 760 ;
the three vapor pressures can be calculated (table 8) and furthermore from p-, the value A f . If we want to get the constant A from the latter, we have to follow the somewhat uncertain path of extrapolating log a', beyond T = 95. If we do this and extrapolate linearly to ii = 98.3 (log a', = 0.076~ 2.0), then log af = 9.47 and A = 20.0 (& = 32G"C., table €3, practically identical with thc corresponding value in table 7, an agreement which, however, should not, be overestimated."
+
16 98.39 (0.918 molc HsS04, 0.082 mole ILO) (64) ; 08.33 (56) ; 08.3 (33,05b) ; 95.5 (G5a, 69) ; 98.54 (132). 17 317°C. (132); 331.7"C. (3); about 330°C. (56); 337-338°C. (33); 338°C. (65a, 60, 95b, 134); see also reference 94a. 18 Thoinas and Barker (120) have carried out a series of experiments very near t o the azeotropic concentration (T = 98.06), which-after due correction-leads t o Agg = 15.80; calculation of the azeotropic boiling point from this value would give a figure slightly below 360°C.
271
VAPOR PHASE ABOVE SULFURIC ACID-WATER SYSTEM
With sonie confidence in this last value-at least relative to the other coeffi20.0 (table 5 , column cients of the vapor-pressure formula-we get -4,= A: 3), and hencc p , in its variat:ion ivith concentration and temperature. This
+
-
. ~ . ~
b; _____
1
.P;
WP,
A,
Aj
A
172 185 204
232 215 252
16.31 16.23 16.15
( b)
-3.67
19.98 19.90 19 I82
"C.
326 332 338 13)
(h)
112.0 137.4 167.5
356 330 301
See footnote 17. See table 5 .
makes it possible to give an at least approsiinate survey of the H2SOIcont'ent of the vapor phase. V. SUHVEY OF THE
H2S04 CONTENT
OF THE VAPOR PHASE"
A . Survey for the range ?T < 96 This survey is given in tables 9 and 10. The variation of the sulfuric acid content in the vapor phase, both with temperature and with concentration, is rather peculiar. The curves of equal concentration pass through a maximum or tend to one; the isotherms cross each other (figure 2). The cause of this behavior may he found in the fact that, with increasing concentration, the molal heat of vnporizntion of the water component, ,oh,in its increase and the mold tirut, of vaporizst8ionof the sulfuric acid component A , in its dccrense tend towhrds the same value." 19 The following numerical values seem to give a true picture of the composition of the vapor phase, but) it cannot be expected that each figure is sufficiently accurate to satisfy esactly the t.hermodynamic relationship between the partial pressures of the components. See references 33, 113, 133. 20 Approsimately,
h d g ) * log P,
-
loa ,"P,
tlicrc lo rc,
wlicre
Table 11 shows in round figures A, and the difference A T - m A r for various concentrations and temperatures. See also references 3, 57, 80, 130, 131.
272
E. ABEL
Figure 3” gives on the basis of the preceding data a graphical representation of the composition of the coexisting phases, showing the liquid curve L ( T per cent) and the vapor curve T’ ( T ( g ) per cent H2S04) plotted against the boiling points (at 1 atm.) (see 7, 30, 33, 50, G5a, 68, 7Ga, 133) (BtoC.)(table 121, and gives in this way the boiling-point intervals.
B. Survey f o r the range 96 < T < l o o z 2 On approaching pure sulfuric acid, “monohydrate”, the water vapor pressure decreases considerably in the whole range of temperature, in coexistence with considerable HzS04- and S03-pressures,23 according to the dissociation equilibrium of H2S0,(g). This state of affairs which follows from thermodynamics leads to peculiar conclusions about the range of stable existence of highly concentratted and pure sulfuric acid as shown in table 13. The figures in this table are based on the simplest possible assumption that the log &curve may be extrapolated linearly up to T = 1 0 0 . ~ ~ Following this assumption the temperatures related to the figures in heavy type mould be near to the boiling points (at 1 atm.) and the existence of such
7r
An
AI
-_ An -
A,
WAr .~ -----
25 50 60 70 80 90 05
31.8 (27.0) 24.6 22.4 20.2 18.5 18.3
21.0 (16.0) 12.0 9.0 5.0
31.7 26.8 23.8 20.7 18.7 1.5 17.8 17.4 -0
21.0 16.0 12.0 7.0 4.0 1.7 -0
3OOOC.
-- --
13.2 19.7 17.7 17.1 16.8
ArwAr
AI
$:
A*
-- _ _ -
12.0 7.0 3.3 17.0 1 . 6 16.5 -0 16.1
A=
- WAT
3 . 0 16.0 2.7 1.o 1.5 15.6 4 15.3 Probably 14.5 Probably negative 14.6 1ne;:ve
1
(a)
See Appendix, tflble 15.
For thc sake of clarity the abscissa is drawn up to r ( g ) = 8 (dotted) in two scales. **With regard to the vapor pressure at the aacotropic concentration, see paragraph IV,C. Experimental material above this concentration consists niainly of an experiment by Thomas and Barker (120) (ir = 99.23); their results can be interpreted according to the survey of these highest concentrations. 2 3 Inasmuch as the process of boiling a t T -+ 100 is closely connected with the reaction (Bee, e g., reference 95b) 21
€TL80a(~)
-+
SOi(g)
+ €TLO(R)
an aulomntic Imalc operatcs: thc boiling point will quickly “run up” the boiling curve until the azeotropic concentration is reached. This fact explains the many cliscrcpnncics in the literature as t o the temperaturc of “boiling” sulfuric acid. 1 4 Should the log u:-curve above ir = 95 or 98 bend up or down, the peculiarities mentioned above would be either intensified or moderated.
VAPOR PHASE ABOVE SULFURIC .4CID-WATER
@4 c a 1w .
c?
3 % 2% I. M ri
9B
3
1 i IS/
m
m
h h m O ? ” ? xxo ooo
3 h
‘9 3
SYSTEM
273
E. ABEL
274
zh .C1
D
rs a
45 I
I
tnn
4
( ~ ( 8 )versus ) welgtlt
sulfuric acid in I
per cent of P
I I
I---I
-----___
I
FIG. 3. Phase diagram: coexistence between the liquid phase and its vapor of 1 atmosphere; boiling-point intervals.
275
276
E. ABEL
highly concentrated sulfuric acid (at 1 atm.) above these temperatures would have to be looked upon as the existence of an unstable overheated liquid.26 This may be true for stoichiometric monohydrate, HzS04, at even rather low temperatures. From the thermodynamic point of view the conclusion cannot be avoided that under normal conditions of pressure the range of temperatures in which highly concentrated sulfuric acid exists as a stable liquid is considerably limited. TABLE 12 ?r
...............................
I I
.................
80
I I
85
p r , mm. H g . . . . . . . . . . . . .
202 0.2
225 2.2
n ( g ) .....................
"0.14
-1.3
-0.07
4 . 7
Bt>'C...
*.(g) (a)
x
103.. . . . . . . . . . . .
-I
I
90
255
11 8.0 3.3
I I
93.19(')
I I
95
275
290
19 19
63 33 18
5.7
66"B.
Appendix The evaluation of a number of partial values of the water component in the course of the treatment of the sulfuric acid component suggests the establishment of a similarly based vapor-pressure formula for the water component as well; 'this formula has been found quite satisfactory for orientation about the water vapor pressure, .especially at high concentrations and temperatures. Let ,Jbe the heat of evaporation of water, ,L, the relative partial molal heat content and w A , the heat of evaporation of H2O (r);furthermore
then log wp* = ,A,
1 dT +/- (d- wL) R" T 2
26 Such an overheating is greatly favored and may even be caused by the extraordinarily effective "negative catalysis" consisting in the automatic formation of HzO in the boiling liquid phase. In fuming sulfuric acid (652, 72, 94c) (oleum) sulfuric acid acts apparently merely as a solvent for so3; the partial pressure of the latter seems t o have as little connection with the thermodynamic SO3pressure .p* as, e.g., the oxygen partial pressure of hydrogen peroxide, saturated with air, has with the oxygen pressure corresponding t o the equilibrium 2H202 e 2H2O 0 2 . These considerations seem to exclude the existence of any dissociation of HZS04 into H?O and SO3in the liquid phase. It is beyond the scope of this paper to discuss the technical means of producing sulfuric acid of very high concentration or free of water; i t may be remarked, however, that the combination of H 2 0and SO3to yield H2S04can obviously be achieved only under conditions in which the impressed SOspressure exceeds the "latent" partial pressure .prof the sulfuric acid to be dehydrated.
+
VAPOR PHASE ABOVE SULFURIC ACID-WATER SYSTEM
01 01 h
II k
-
0
n II k
I
ri ri
277
278
E. ABEL i
TABLE 14 The coejicients of the formula for the water vapor pressure ,pr ( w ~ in r
-- -l 3.18 3.03 3.13 3.24 3.40 2.98 2.87 3.41, 4.83 4.31
50 55 60 65 70 75 80
85 90 95
mm. Hg)
15OOC. ~
3.99 G.044 21.59 0.120 17.86 2.65 0.065 18.95 3.10 3.65 -0.011 20.22 22.62 4.70 -0.15 0.38 -3.40 -6.85 0.56 -4.85 0.63 0.22 9.85 0.76 0.28
21.58 17.84 18.92 20.17 22.55 2.26 -6.67 37.66 13.91
21.49 21.46 17.80 17.79 18.85 18.84 20.10 20.08 22.48 22.43 2.17 2.13 -6.70 -6.71 -0.25 -0.27 37.63 37.57 13.92 13.95
200°C.
vetage(') -
20.05 22.42 2.11 -6.74 -6.71 -0.28 -0.25 37.60 37.60 13.98
21.47 17.87 18.89 20.10 22.48 2.16 -6.70 -0.26 37.61 13.95
I n some cases,the average has been taken with due regard t o the weight of the data.
TABLE 15(a) Molal heats of vaporization, ,A,, i n kilogram-calories U
50 60 70 75 80 85 90 95 (8)
25'C.
100°C.
1SO'C.
200'C.
11.35 12.10 13.30 14.05 15.00 16.10 17.10 18.15
10.65 11.50 12.95 13.70 14.70 15.40 16.15 17.40
11.10 12.75 13.35 14.00 14.70 15.55 16.80
13.90 13.90 15.05 16.15
250'C.
300°C.
13.35 (12.95) 14.55 15.40
14.10 14.65
340OC.
,
13.80 13.95
See table 11 in fooinote 20.
where 0 .
The values (T 5 50) for :Lr and ALC&, appear together with the corresponding values for HzS04, the former from the heat of mixing (table 3, column 5 ; see also footnote 6), the latter from the specific heats; those values which lead to 26
See footnote 4.
VAPOR PHASE ABOVE SULFURIC ACID-WATER SYSTEM
A”,:’,
279
are entered in table 4 (columns 9-13), where ,C(g) has been assumed
to be independent of temperature in the relevant range. From these data the coefficients ,B,, ,D,, and ,E, of the vapor-pressure formula are calculated (table 14); the constant of integration ,A, had been evaluated from ,au in the range where the total and water vapor pressure are practically identical. Its value is seen to be satisfactorily constant (table 14, columns 5-11). Table 15 gives a summary of the molal heats of vapwization of HzO(r) obtained on this basis. VI. SUMMARY
1. On the basis of thermodynamic relationships an expression for the partial vapor pressure of HzS04 ( p , ) in the vapor phase above the liquid system sulfuric acid-water (a per cent HzS04) has been developed :
2. The coefficients of this vapor-pressure formula can be calculated from the activity of the sulfuric acid component at a given temperature, 7 (298”K.), in its dependence on concentration (a),from the dissociation constant K , of sulfuric acid vapor in its dependence on temperature, and from thermal data which can be obtained from the existing experimental literature, although in many cases only approximations are available. 3. The constant A , , which is a function of the concentration, contains a term independent of the concentration; this term contains the entropy of formation of HzS04in its standard state from HzO(g) and SOs(g) in their standard states. 4. From the (sparse) observations given in the literature on the vapor pressure of sulfuric acid above the system HzS04-Hz0, a constant can be obtained the value of which is in agreement with that of the entropy of formation men- , tioned above as far as can be expected from its accuracy. 5. On the basis of this result, which seems to indicate a proper evaluation of the coefficients of the above vapor-pressure formula, an attempt has been made to gain an insight into the composition of the vapor phase in a wide range of concentration and temperature. G . Beyond the azeotropic concentration, approaching pure sulfuric acid, conditions seem to arise at relatively moderate temperatures in which, from the thermodynamic point of view, sulfuric acid appears to be “overheated”. 7. The dependence of the water vapor pressure on the composition of the liquid system served as a means of calculating the activity of the sulfuric acid component in the range of higher concentrations. 8. The evaluation of partial values of the system HzS04-Hz0 which was necessary for the above purposes suggested the calculation of a vapor-pressure formula for the water component as well, a formula which proved to be useful.
I am indebted to my friend and colleague Mr. J. M. Fanto for having pointed out to me a discussion (76b) of the problems of sulfuric acid which has led me
280
E. ABEL
to this investigation; I also thank Professor and Mrs. Ph. Gross and Dr. H. Tompa for clarifying conversations and Mrs. B. B. Silk for her painstaking translation. REFERENCES
,
1 (1) AKERL~F, G.: J. Am. Chem. SOC.48, 1160 (1926). (2) BECKER, G., A N D ROTH,W. A.: Z.physik. Chem. A169, 291 (1934). (3) BECKMANN, E.: Z. physik. Chem. 63, 129 (1905). (4) BERTHOUD, A.: Helw. Chim. Acta 6, 513 (1922). (5) BICHOWSKI, F. R.: J. Am. Chpm. SOC.44, 130 (1922). (6a) BICHOWSKY, F. R., A N D ROSSINI,F. D.: The Thermochemistry of the Chemical Substances. Reinhold Publishing Corporation, New York (1936). (6b) BIRON,E.: J. Russ. Phys. Chem. SOC.31, 171 (1899). ( 7 ) BLAKE,F. C., AND GREENEWALT, C. H . : International Critical Tables, Vol. 111, p. 302. McGraw-Hill Book Company, Inc., New York (1928). (8) BLUECKE, A.: Ann. Phys. Chem. 23, 161 (1884). (9) BODE,F.: Z. angew. Chem. 1889, 244. (10) BODENSTEIN, M., AND KATAYAMA, M . : Z. Elektrochem. 16, 244 (1909). (11) BODENSTEIN, M., AND POHL, W.: Z. Elektrochem. 11, 373 (1905). (12a) BOSE, E.: Z. Elektrochem. 14, 269 (1908). (12b) BRIGQS,E.: J. SOC.Chem. Ind. 22, 1275 (1903). (13) B R ~ N S T EJ. D ,N.: Z. physik. Chem. 64, 641 (1908); 68, 693 (1910). (14) BRYANT, M. M. D.: Ind. Eng. Chem. 25, 820 (1933). (15) BURT,B. C.: J. Chem. SOC.86, 1339 (1904). (16) CATTANEO, L.: Nuovo cimento [3] 26, 50 (1889). (17) CHERNOBAEV, D. A.: J. Chem. Ind. (U.S.S.R.) 14, 1235 (1937). (18) COLLINS,I$. M.: J. Phys. Chem. 37, 1191 (1933). (19) De LA CONDAMINE, C . : Ind. chim. 6, 153 (1918). (20%) COWPERTHWAITE, I. A., AND SHRAWDER, J.: J. Am. Chem. SOC.66, 2345 (1934). (20b) CRAIG,D. N., AND VINAL,G. W.: Bur. Standards J. Research 24, 475 (1940). (21) CROWTHER, E. M., AND PURI,A. N.: Proc. Roy. SOC.(London) 106A, 232 (1924). (22) DAUDT, W.: Z. physik. Chem. 106, 225 (1923). (23) DAWSON, H. M.: Proc. Leeds Phil. Lit. SOC.2,359 (1933). (24a) DEE,T. P.: J. SOC.Chem. Ind. 64, 40 (19451; see first remark in footnote (c) of table 1. (24b) DIETERICI, C.: Wied. Ann. 42, 513 (1891); 60,47 (1893); 62,616 (1897); 67,865 (1899). (25) DOMKE,J., A N D BEIN,W.: ,Z. anorg. Chem. 43, 148 (1905). (26) EASTMAN, E. D.: U. S. Bur. Mines Tech. Paper No. 446 (1929). (27) EBERT,H.: Z. Instrumentenk. 60, 43 (1930). D.'R., AND ROSSINI,F. D.: Bur. Standards J. Research 3, 597 (1929). (28) ECKMANN, (20) FENNING, R . W., A N D WHIFFIN,A. C.: Phil. Trans. Roy. SOC.London A238, 149 (1939). (30) FERQUSON, A. L.: J . SOC.Chem. Ind. 24, 781 (1905). (31) FERGUSON, A. L., A N D FRANCE, W. G.: J. Am. Chem. SOC.43, 2150 (1921). (32) FRAZER, J. C. W., A N D LOVELACE, €3. F.: J . Am. Chem. SOC.36,2439 (1914). (33) FURNAS, C. C.: In Rogers' Manual of Industrial Chemistry,6th edition, Vol. I, p. 303. D. Van Nostrand Company, Inc., New York (1942). (34) GORE,H. C.: J . Biol. Chem. 16, 259 (1913). (35) GREENEWALT, C. H . : Ind. Eng. Chem. 17, 522 (1925). (36) GRAU,R., A N D ROTH,W. A . : Z. anorg. allgem. Chem. 188, 173 (1930). (37) GROLLMAN, A. A N D FRAZER, J. C. W.: J. Am. Chem. SOC.47, 712 (1925). (38) HACKER, A . : Ann. Physik [41 39, 1342 (1912). W. J.: J. Ani. Chem. SOC.67, 9 (1935). (39) HAMER, (40) HAMER,W. J.: J . Am. Chem. SOC.66, 860 (1934); 67, 9 (1935).
VAPOR PHASE ABOVE SULFURIC ACID-WATER
SYSTEM
28 1
A. (AND KARV&,D.) : Ber. 68, 957 (1925) ; z. anorg. allgem. Chem. 206, 167 (1932). HARNED, H. S., A N D AKERLOW,G.: Physik. Z. 27, 411 (1926). HARNED, H. S., AND HAMER,W. J.: J. Am. Chem. SOC.67, 27 (1935). HARNED, H. S., AND STURGIS, R. D . : J. Am. Chem. SOC.47,945 (1925). HARTUNG, E. J.: Trans. Faraday SOC. 11, 64 (1915). (46a) HAUCHT,A. P.: Chem. Met. Eng. 42, 278 (1935). (46b) HELMHOLTZ, H . v.: Wied. Ann. 27, 532 (1886). (47) HERRMANN, C. V.: Ind. Eng. Chem. 33, 898 (1941). (48) HORSCH,W. G.: J. Am. Chem. SOC.41, 1787 (1919). (49) HUPBORN, R. I.: Proc. Phys. SOC.(London) 40, 249 (1928). (50) ISHIKAWA, F.: Bull, Inst. Phys. Chem. Research (Tokyo) 13, 1027 (1934). (51) ISHIKAWA, F., A N D HAGISAWA, H.: Bull. Inst. Phys. Chem. Research 13, 1019 (1934). (52) KAPUSTINSKI~, A. F., A N D SHAMOVSKI?, L. M.: Acta Physicochim. U.R.S.S. 4, 791 (1936). (53) KELLEY,K . K . : U. S. Bur. Mines Bull. No. 371 (1934); No. 394 (1936). (54) KELLEY,IC K.: U. S. Bur. Mines Bull. No. 383 (1935). (55) KELLEY,K. K . : U. S. Bur. Mines Bull. No. 406 (1937). (56) KNIETSCH,R.: Ber. 34, 4069 (1901). (57) KOLOSSOWSKY, N. DE: J. chim. phys. 23, 353 (1926). 3, 601 (1934). (58) KUDRYAVTZEV, B. B.: Compt. rend. acad. sci. U.R.S.S. (59) LANGE,E., MONHEIM, J., A N D ROBINSON, A. L.: J. Am. Chem. SOC.66, 4733 (1933). (60a) LATIMER,W. M.: Oxidation States of the Elements and their Potentials in Aqueous Solutions. Prentice-Hall, Inc., New York (1938). (60b) LATIMER, W. M., HICKS,J. F. G., JR., A N D SCHUTZ, P. W.: J. Chem. Phys. 1, 620 (1933). (61) LATIMER, W. M., SCHUTZ, P. W., A N D HICKS, J. F. G., JR.:J. Chem. Phys. 2,82 (1934). (62) LEHFELDT, R . A.: Phil. Mag. [5] 40, 402 (1895). (63) LEWIS,G. N., A N D LACEY,W. N.: J. Am. Chem. SOC.36, 804 (1914). M.: Thermodynamics and the Free Energy of Chemical (64) LEWIS, G. N., A N D RANDALL, Substances. McGraw-Hill Book Company, Inc., New York (1923). (65a) LUNGE,G.: Ber. 11, 370 (1878). (65b) LUNGE, G . : Z. angew. Chem. 1889, 272. (65c) PVICDAVID, J. W.: J. SOC.Chem. Ind. 43, 57 (1924). (66) MCDOUGALL, F. H., AND BLUMER, D. R.: J. Am. Chem. SOC.66, 2236 (1933). (67) MCHAFFIE,I. R . : J. Am. Chem. SOC.48, 1143 (1926); J. Chem. SOC.1927, 112. Reference 33, Vol. I, p. 303. (68) MANTIUS,0.: (69) MARIGNAC, C. : Arch. Sci. 39,217 (1870) ; Ann. 8, Suppl., 335 (1872) ; Ann. chim. phys. [4] 7, 385 (1871). (70) MEYEREN, W. v.: Z. physik. Chem. A160, 272 (1932). (71) MILES, F. D., NITBLOCK, H., A N D SMITH,D.: Trans. Faraday SOC.40, 281 (1944); see first remark in footnote (c) of table 1. (72) MILES,F. D., NITBLOCK, H., A N D WILSON,G. L.: Trans. Faraday SOC.36,345 (1940). (73) MORGAN, R. A.: l a d . Eng. Chem. 34, 571 (1942). (74) ODDO,G., AND ANELLI, G.: Gaze. chim. ital. 1911, 552. (75) OBERMILLER, J., A N D GOERTZ,M.:Z. physik. Chem. 109, 145 (1924). (76a) PARRISH, P., A N D SNELLING, F. C.: S d p h u r i c Acid Concentration, Vol. 1. Ernest Benn, Ltd., London (1924). (76b) PARRISH, P.: SOC.Chem. Ind., Chem. Eng. Group. Proc. 23, 1 (1941). (77) P A S C A L , P., . ~ N DG A R N I E R : Bull. S O C . chim. 27, 8 (1920); MBm. poudres 20, 29 (1923). (78) PERRY,I. H., AND DAVIS,D . S.: Chem. Met. Eng. 41, 188 (1934). (79) PERRY, I. H., A N D DUNS,H. C.: Chem. Met. Eng. 41, 74 (1934). C. C.: Ann. Physik 70, 302 (1847). (80) PERSON, IIANTzsCH,
E. ABEL
PFAUNDLER, L.: J. prakt. Chem. 101, 567 (1867); Ber. Akad. Wiss.Wien 100, 352
.
*
(1891). PFAUNDLER, L.: Ber. 3, 798 (1870); Ber. Akad. Wiss. Wien 71, 11, 155 (1875). PICKERING, S. U.: Proc. Roy. SOC.(London) 49, 11 (1891); J. Chem. SOC.67, 664 (1895). PICKERING, S. U.: J. Chem. SOC.67, 94 (1890). PORTER, A. W.: Trans. Faraday SOC.18, 373 (1918). PRETAT, M.: MBm. poudres 24, 119 (1930-31). LORDRAYLEIGH: Phil. Mag. [SI 4, 521 (1902). RANDALL, M., A N D CUSHMAN, 0. E.: J. Am. Chem. SOC.40,393 (1918). RANDALL, M., AND LANGFORD, C. T.: J. Am. Chem. SOC.49, 1445 (1927). RANDALL, M., A N D ROSSINI,F. D.: J. Am. Chem. SOC.61, 323 (1929). M., A N D SCOTT,G. N.: J. Am. Chem. SOC.49,647 (1927). RANDALL, RANDALL, iM., A N D TAYLOR, M. D.: J. Phys. Chem. 46,959 (1941). RANDALL, M., AND VANSELOW, A. P. : J. Am. Chem. SOC.46,2418 (1924). (94%) REDLICH, O., A N D SCHUTZ, P. W.: J. Am. Chem. SOC.66, 1007 (1944); see first remark in footnote (c) of table 1. H. V.: Bnn. Chem. Phys. [3] 16, 179 (1845). (94b) REGXAULT, (94c) REMY,H., A N D MEINS,W.: Ber. 76B,1901 (1943); see first remark in footnote (c) of table 1. (95a) RICHARDS, T. W., A N D MATHEWS, J. H.: Proc. Am. SOC.Testing Materials 46, 511 (1911). (95b) READ,W. T.: Industrial Chemistry, 3rd edition. John Wiley and Sons, Inc., New York (1945). R . A.: Trans. Faraday SOC.36, 1229 (1939). (96) ROBINSON, (97) ROSCOE, H. E. : J. Chem. SOC.13, 146 (1860) ; Ann. 116, 203 (1860). (98) ROSSINI,F. D.: Bur. Standards J. Research 4, 313 (1930); 6, 791 (1931); 7, 47 (1932). (99) ROTH,W. A.: Z. Elektrochem. 38, 94 (1932). (100) ROTH,W. A.: Landolt-Bornstein Tnbellen (5), 2. Erg. Bd., p. 1500. Julius Springer, Berlin (1931). (IOla) ROTH,W. A , , GRAU,R., AND MEICHSNER, A.: Z. anorg. allgem. Chem. 193, 161 (1930). (101b) RUMELIN,G . : Z . physik. Chem. 68, 449 (1907). (102a) SCATCHARD, G., AND EPSTEIN,L. F.: Chem. Rev. 30, 211 (1942). G., HAMER,W. J., AND WOOD,S. E.: J. Am. Chem. SOC.60,3061 (1938). (102b) SCATCHARD, H.: Physik. Z. 10, 210 (1909). (103.) SCHLERINGER, A. R.:J. Am. Chem. soc. 61,2370 (1939). (104) SH.4NKMAN, S., A N D GORDON, (105) SHEFFER, H., JANIS, A. A., . ~ N DFERGUSON, J. B.: Can. J. Research 17B, 336 (1939). ' &I.S., A N D LYONS, E. H., J R . :J . Am. Chem. SOC.64, 979 (1932). (106) SHERRILL, (107~~) SHRAWDER, J., JR.A N D COWPERTHWAITE, I. A.: J. Am. Chem. SOC.66. 2340 (1934). (107b) SIMONS, I,.: Soc. Sci. Fennica Commentationes Phys. Math. 7, 0 (1933). (108a) SMITH,A . W.: Phys. Rcv. 33, 173 (1911). (108b) SMITH,D. F., A N D ~ ' I A Y EJ. R ,E.: J . .4m. Chem. Soc. 46, 75 (1924). (109) SMITS,.4.:Arch. n6erland. x i . [2] 1, 97 (1898). (110) SMITS,A.: Z. physik. Chem. 39, 385 (1902). P.: J. Chem. SOC.126, 2554 (1921);1926, 1108. (111) SMITS,A., A N D SCHOEXMAKER, (112) SOREL,E.: B d l . soc. ind. Mulhouse 69, 240 (1889); J . SOC.Chem. Ind. 9, 175 (1890). , (113) SPROESSER, W. C.: Private communication in the files of The duPont Company. D. P.: See reference 132. (114) STEVENSON, (115) STOCKMAYER, W. H., KAVANAGH, G. M., A N D MICKLEY, H . S..:J. Chem. Phys. 12. 408 (1944); see first remark in footnote (c) of table 1. (116) SSOKOLIK, A. (SOCOLIK, A. S.) (ANDSAVARIZKY): Z. physik. Chem. A168, 305 (1932); Chem. J. Sei. A, J. Allgem. Chem. 2 (64), 311 (1932). G.: Mem. Akad. Petersbourgh [7],35 (1887); Z. physik. Chem. 2,42 (1888). (117) TAMMAR",
'
'
COMMUXICATION TO THE EDITOR
283
T A Y L O RG., B., A N D L E H N E RS.: , Z . physik. Chem., Bodenstein Festband, p. 30 (1931). THACKER C., M., FOLKIN, H. O., AND MILLER,E. L . : Ind. Eng. Chem. 33,584 (1941). , F . : J. Chem. SOC.127,2520 (1925). T H O M A SJ., S., AND B A R K E RW. T H O M A SJ., S., AND R A M S A YA,. G . : J. Chem. SOC.123, 3256 (1923). THOMSEN, J.: Thermochemistry, translated by K. A. Burke. Longmans, Green and Company, London (1905). TIMOSHEV V., G . , A N D ABRAMOVA, A . v.: J. Chem. Ind. ( U . S . S . R . ) 17, NO. 12, 24 (1940). T O V B I NM. , V.:Univ. Btat Kiev, Bull. Sci. Rec. Chim. 3, 221 (1937). T R I M B L EH. , M., AND E B E R TP. , F . : J. Am. Chem. SOC.66,958 (1933). T U R K H A NE., Y a . , AND YIJDINA, V. I.: J. Chem. Ind. (U.S.S.R.) 16, No. 12 (1938). VOSBUROH, W. C., A N D CRAIG,D. N . : J. Am. Chcm. SOC.61, 2009 (1929). H.: Proc. Leeds Phil. Lit. SOC.Sci. Sect. 1, 97 WHITLAW-GRAY, R . , AND WHITAKER, (1926). WILSON,R . E.: J. Ind. Eng. Chem. 13, 326 (1921); J. Am. Chem. SOC.43,721 (1921). WREWSKY,M. S.: J. Russ. Phys. Chem. SOC.69, 69 (1927); Z . physik. Chem. A144, 244 (1929). WREWSKY,M. S., AND X I K O L S K YB,. : J. Russ. Phys. Chem. SOC.69, 77 (1927). YOST,D. M.,AND RUSSELL,H., J r . Systematic Inorganic Chemistry. Prentice-Hall, Inc., NewYork (1944). ZEISBERG, F . C.: Trans. Am. Inst.. Chem. Eng. 14, 1 (1922).
COMMUNICATION TO THE EDITOR EQUILIBRIUM SPREADING COEFFICIENTS OF AMPHIPATHIC ORGANIC LIQUIDS ON WATER Heymann and Voffe (J. Phys. Chem. 49, 2 3 9 4 5 (1945)) have recently published their reasons for believing that the equilibrium spreading coefficient on water of amphipathjc organic compounds is always a small negative value, approximating - iWk,where Wk is the contribution of the polar groups t o the work of cohesion of the organic phase. The writer has recently (J. Phys. Chem. 48, 75 (1944)) taken exception t o their reasoning as disclosed in an earlier note (J. Phys. Chem. 47, 409-10 (1943)). From their subsequent complete publication (lac. cit.) it appears more definitely that they have omitted certain material factors in the molecular and mathematical developments of their theory. Their argument, on the basis of an analysis of molecular forces (J. Phys. Chem. 49, 239-45 (1945), part 11),seems to err, or a t least t o lack definiteness, in regard to the location of the cross section BB', the assumed plane of separation in considering work of adhesion. Their argument assumes that separation is made between an oriented layer in the organic phase and the unoriented organic phase. While it is true that separation of the liquid column at AA' does correspond to the work of cohesion of the oil phase, in that two new unit areas of oil phase-air interface are formed, it does not seem to be true that separation a t BB' corresponds to the work of adhesion (oil phase-water phase). The assumed plane of separation, BB', lies above the oriented layer in the oil phase and presumably
