Journal o/'Sohttion Chemistry, Vol. 9, No.

10, 1980

Thermodynamics of Aqueous Mixtures of

Nonelectrolytes. I. Excess Volumes of Water -
n-Alcohol Mixtures at Several Temperatures
George C. Benson 1,2and Osamu Kiyohara 3
Received February 19, 1980; revised May 29, 1980

Excess vohlmes 0/' binary mixtures c~/" water with methanol, ethanol and
l-propanol were obtained from density measurements at 5 degree intervals from
15 to 35~ over the entire composition range. Excess thermal expansion
cor partial molar excess volumes, and expansJbilities at 25~ were
derived.from the results. The significance Of these values is discussed in relation
to tTypothesized structural changes in the mixtures.

KEY WORDS: Melhanol; ethanol; 1-propanol; aqueous alcohol mixtures;

excess volumes; partial molar volumes; thermal expansibililies.

1. I N T R O D U C T I O N

The many practical applications of aqueous n-alcohol mixtures

have led to extensive thermodynamic and spectroscopic studies of their
properties. (~,2~However, there have been relatively few investigations of
their thermal expansibilities such as are reported here.

2. EXPERIMENTAL

2.1. Malerials

Methanol and 1-propanol (Fisher Certified), and ethanol

(Consolidated Alcohols Ltd.) were further purified in a preparative gas
chromatograph (F&M Model 775) using a column filled with Porapak
Q. The final products were stored over a molecular sieve 3A (BDH).

lDivision of Chemistry, National Research Council of Canada, Ottawa, Ontario, Canada KI A 0R6.

2To whom correspondence should be addressed.

3NRCC Research Associate 1975-79. Present address: Chemicals Inspection and Testing Institute,
Tokyo, Japan.

791
0095-9782/80/ 000-0791503 00/001980 Plenum Publish ng Corporation
792 Benson and Kiyohara

In spite of these precautions, analysis by the Karl Fischer method

indicated the the presence of residual water (usually less than 0.1
percent by mass) in the samples used for the mixtures. Densities p of
the pure alcohols were estimated by extrapolating the observed
densities to zero content of water. Some measured physical properties
of the pure alcohols are given in Table I and are compared with results
from the literature) 3,4~
Mixtures with deionized distilled water were prepared by mass,
taking into account the effect of buoyancy. No attempt was made to
eliminate dissolved air. A correction for the water content of the
alcohol was included in calculating the mole fraction. The error of the
mole fraction is estimated to be less than 2 x 105.

2.2. Measurements of Density

Densities of the mixtures were determined with a flow type
oscillating tube densimeter (Sodev Inc., Model "O2D). Details of the
apparatus and its operating procedure have been described
previously. (5,6) The densimeter was calibrated, assuming a linear
relation between the density of the fluid and the square of the oscillator
period. Previously (6~ we noted that the point for water may deviate
considerably from this relationship, depending on the driving power
applied to the oscillating tube. In the present work, this power was
adjusted at each operating temperature to minimize the deviations of
the points for dry nitrogen gas, water, and four organic solvents whose
densities had bee determined pycnometrically.
After the preliminary adjustment of the power, measurements for
the mixtures were interspersed with measurements for nitrogen and
water. Densities of the mixtures were then obtained using calibration
constants derived from the nitrogen and water results. The values o f p
(and ~) adopted for ordinary water (Standard Mean Ocean Water or
SMOW) were calculated from the equation given by Kell (7) and are
included in Table I for ease of reference. The temperature of the
densimeter was controlled within -I-2 x 10 -3 ~ at the five operating
tempe.ratures. Measurements of densities were reproducible to better
than 5 ppm. The uncertainties of the temperature intervals and of the
values of the density are estimated to be less than 5 x 10-3 ~ and 2 x
10-5 g-cm 3, respectively.
Volumes of Water-Alcohol Mixtures 793

Table I. Refractive Indices, Densities and Coefficients of Thermal

Expansion for the Component Liquids

t~ Obs. Ref. 3 Ref. 4 Ref. 7

Methanol Seawater a
no 25 1.32645 1.32652
15 0.795803 0.79599 0.79573 0.999103
20 0.791102 0.79131 0.79105 0.998207
-3
p/g-cm 25 0.786350 0.78664 0.78636 0.997048
30 0.781666 0.78196 0.78165 0.995650
35 0.776991 0.77729 0.77692 0.994035
~/kK -1 25 1.201 1.t89 1.196 0.2572

Ethanol

nO 25 1.35925 1.35941
15 0.793495 0.79362 0.79346
20 0.789235 0.78937 0.78921
p/g-cm -3 25 0.784962 0.78509 0.78493
30 0.780667 0.78078 0.78063
35 0.776380 0.77645 0.77629
c~/kK q 25 1.092 1.094 1.093

1-Propanol

no 25 1.38314 1.38370

15 0.807403 0.80771 0.80752

20 0.803487 0.80376 0.80360
-3
p/g-cm 25 0.799353 0~79976 0.79965
30 0.795470 0.79571 0.79565
35 0.791411 0.79162 0.79160
a/kK-1 25 1.003 1.006 0.995

astandard Mean Ocean Water(SMOW).

 ??PPPPPP ???PPP?PP ?P?PPP?PP?? ??????P~??? ?PPP?P?PP?
?????P~? P?P??P?? PP~P~?P???? Pg~P????P?P pp?p?Pg?p?
r~
§
o o o o o o o ~1 o o o o o o o o ~ o o o o o o o o o o o ~1 ~ o o o o o o o o o o II o o o o o o o o o o ~
c~
o
ooooooo ??pppp?? ?p?ppppp?pp pp~ppppp?pp pppp??gp??
~&&.&'L~& "&&'~''' &'&~'~''''' o o o' o o' o o' ' ' ~ ' " & ' ' o o o' o o' o o' o o.o ~. . . . .
?PPP~???? ?PP?P??PPP?P ?PPPPPPP???P? ????????~? ?P~P?P~
@
PP?PPPP? PP?PPPPPPP? P?P~P?PP~?P~ ?P?PP~?~PP ?P~g???~?
I l l ~ , ~ , ~ l l ~ l l l l l l I l l l l ~ l l l l l , ~ I ~ l l ~ l l l , , I J l l l l , , I
5
o ~ ~ ~ ~ ~ ~ ~ ~ ~
. . . . , , , , g & ~ g ~ & g g ~ g ~ g ~ & g & & g & g ~ & ~ & & & ~ g ~
eae4o/~!)l pue uosua8 t,6L
Volumes of Water-Alcohol Mixtures 795

Table II. (concluded)

x V~/cm~mol -: x V~/em3mol
~ -I x V~/em3mol -~ x V~/em3mol -I

xH20 + (I-i)C~H~OH

T/K : 288.15
0.02775 -0.0854 0.39802 -0.6424 0.86151 -0.5658 0.97038 -0.1663
0.03751 -0.1131 0.44268 -0.6690 0.89902 -0.5030 0.97540 -0.1330
0.09709 -0.2586 0.49446 -0.6909 0.94080 -0.3603 0.97994 -0.1039
0.15998 -0.3747 0.5431,2 -0.7040 0.94944 -0.3084 0.98606 -0.0674
0.22780 -0.4789 0.60286 -0.7097 0.95285 -0.2861 0.98778 -0.0579
0.24653 -0.5035 0.66001 -0.7037 0.95287 -0.2861 0.99041 -0.0437
0.24833 -0.5019 0.70038 -0.6920 0.96157 -0.2267 0.99367 -0.0273
0.33842 -0.5977 0.74341 -0.6728 0.96425 -0.2082 0.99490 -0.0214
0.35696 -0.6129 0.80044 -0.6323 0.96614 -0.1953 0.99726 -O.0110

T/K = 293.15
0.04503 -0.1297 0.49538 -0.6650 0.85375 -0.5511 0.96536 -0.2004
0,06717 -0.1823 0.55790 -0.6790 0.89830 -0.4796 0.97275 -0.1518
0,11876 -O.2916 0.60297 -0.6809 0.91994 -0.4289 0.97507 -O.1369
0.14746 -0.3436 0.60740 -0.6840 0.92929 -0.3984 0.97954 -o.1087
0.20921 -O,4362 0.65362 -0.6789 0.94039 -O.3511 0,98508 -0,0756
0.23834 -0.4746 0.70120 -0.6643 0.94338 -0.3358 0.98962 -0.0501
0.28854 -0.5296 0.74400 -0.6462 0.94996 -0,2990 0.99170 -0.0388
0.34152 -0.5791 0.80106 -0.6o51 0.95491 -0.2686 0.99472 T0.0237
0,41005 -0.6258 0,80430 -0.6013 0,96277 -o.2173 0,99782 -0.0092
0.43915 -0.6440

T/K : 298.15
0.07612 -0.1980 0.55390 -0.6631 0.80387 -0.5827 0.94342 -0.3272
0.10469 -0.2577 0.57454 -0.6661 0.82810 -0.5608 0.94563 -0.3157
0.15366 -0.3420 0.57875 -0.6643 0.83388 -0.5549 0.94968 -0.2950
0.20093 -0.4140 0.60047 -0.6673 0.84477 -0.5425 0.95018 -0.2922
0.20684 -0.4222 0.64707 -0.6611 0.85447 -0.5307 0.95030 -0.2909
0.24297 -0.4672 0.65375 -0.6614 0.87007 -0.5085 0~95433 -0.2679
0.24549 -0.4697 0.67131 -0.6551 0.88871 -0.4792 0.95964 -0.2370
0.29901 -0.5251 0.67757 -0.6546 0.90101 -0.4568 0.96318 -0.2138
0.34487 -0.5666 0.70032 -0.6481 0.90141 -0.4550 0.96657 -0.1926
0.35012 -0.5703 0,70238 -0.6462 0.90248 -0.4538 0.97040 -0.1677
0.40489 -0.6069 0-75079 -0.6228 0.91770 -o.4186 0.97407 -0.1446
0.44432 -0,6293 0.75232 -0.6204 0.92889 -0.3851 0.97578 -0,1345
0.45926 -0.6342 0.77749 -0.6046 0.93378 -0.3682 0.97947 -o.1107
0.47436 -0.6410 0.78270 -0.6017 0.93707 -0.3551 0.98492 -0.O781
0.48008 -0.6431 0.79649 -0.5905 O.94100 -0.3382 0.99013 -0.0486
0.50985 -0.6552

T/K = 303.15
0.02769 -0.0722 0.44372 -0.6003 0.87479 -0.h813 ,0.95499 -0.2591
0.07326 -0.1784 0.49170 -016196 0187654 -0.4821 0.96031 -0.2272
0.11934 -0.2665 0-55155 -0.6365 0.89653 -0.4474 0.96445 -0.2039
0.14862 -0.3150 0,60536 -0.6401 0.91956 -0.3989 0.96980 -0.1708
0.19381 -0.3788 0.64793 -0.6366 0.93068 -0.3652 0.97445 -0.1423
0.20876 -0.4010 0,69604 -0.6247 0.93414 -0.3532 0.97982 -0.1098
0.24096 -0,4392 0.74930 -0.6003 0.94077 -0.3278 0.98558 -0.0756
0.29853 -0.4982 0.80037 -0.5653 0.94533 -0.3078 0.99244 -0.0373
0.34041 -0.5347 0.84964 -0.5156 0.94948 -0.2881 0.99882 -0.0055
0.41249 -0.5842

T/K = 308.15
O,O3574 -0.0883 0.43886 -0.5756 0.89910 -0,4268 0.97061 -O.1662
0.12079 -0.2552 0.49487 -0,6006 0.91643 -0.3914 0.97493 -0.i~04
0.14556 -0.2948 0.55321 -0.6144 0.92638 -0.3665 0.97896 -0.1160
0.20987 -0.3826 0.60390 -0.6195 0.92977 -0.3566 0,98637 -0.0724
0.23587 -0.4133 0.65317 -0.6148 0.93904 -0.3258 0,98933 -0.0553
0.28563 -0.4660 0.69845 -0.6038 0.95C70 -0.2764 0.99200 -0.0408
0.34181 -0,5130 0.75117 -0.5792 O.95584 -0.2507 0.99502 -0.0247
0,34281 -O.5137 0.80426 -0.5428 0.96019 -O.2271 0.99730 -0.0131
0.40365 --0.5568 0.84982 -0.4970 0,98567 -0.1956
796 Benson and Kiyohara

3. RESULTS A N D DISCUSSION

Molar values of the excess volume Vmz are summarized in Table

II. In all cases, x is the mole fraction of water. Some difficulty was
experienced in finding algebraic representations to smooth the results
as functions of temperature as well as composition. Of the various
forms investigated, the most suitable is
Vmz = ~b(l~) E ]' (all + a j ) (1-24~)il (1)
where
= xV,'/[xV," + (l-x) v2"] (2)
is the volume fraction of water stated in terms of the unmixed
components at the particular operating temperature t~ By virtue of
its definition, 4~ is implicitly a function of t through the molar volumes
I/1' and V2" for water and the n-alcohol, respectively. Forms derived
from Eq. (1) by replacing $ with x generally required the use of m o r e
terms to achieve a comparable fit. The ~addition of a quadratic
temperature term in Eq. (1) proved to be unwarranted over the rather
limited temperature range of the present study. The greatest difficulty
occurred in representing the results for 1-propanol mixtures which
required the use of 10 terms in Eq. (1). Although the representation is
satisfactory for most purposes, it gives unreliable estimates for the
partial molar volumes of 1-propanol in very dilute mixtures. A more
satisfactory representation for the range x 0.98 is
VmE = ( 1 4 ) E~ [ a i l + ai2t] (1-~) i~ (3)
Values of the coefficients a~j in Eqs. (1) and (3), determined by a
least-squares analysis in which all points were weighted equally, are
listed in Table III along with the standard deviations o- of the
representations.
Deviation plots comparing the present results at 25~ with values
from the literature (8kl6~ are given in Figs. 1-3. Our values of VmE for
methanol mixtures tend to be numerically greater than those Of
previous workers, but in most cases the agreement is within 0.5%. The
results of Griffiths(~7) and of Pesce and Giacomini (~8) are not included in
Fig. 1 due to their large scatter. For ethanol mixtures our results are
in excellent agreement with those of Minowa et al. (j3~ and with the
earlier work of Osborne et aL 04) The literature values for t-propanol
mixtures (~s-~6~ are scattered fairly widely around our results. Fig. 3 also
reveals the difficulty encountered in fitting our results for 1-propanol
mixtures as a function of both temperature and composition. Thus at
25~ our results have predominately negative diviations from the
Volumes of Water-Alcohol Mixtures 797

Table Ill. Coefficients a and Standard Deviations o- for Least

Squares Representations of M~otar Excess Volumes

H20-MeOH a H20-EtOH a H20-1-PrOH b HeO-I-PrOH c

i ail 103ai2 ail I03ai2 ail 103ai2 all I03ai2

1 -3.4395 -2.52 -3.8223 16.19 -2.3285 17.28 -I.0137 -9.53

2 -2.7782 -4.55 -2.4469 2.36 -1.1611 5.36 -5.4169 76.18
3 -0.9334 -17.28 -1.1075 -25.96 -1.6573 19.41 10,8632 130.75
4 -1.0267 1.77 -3,0729 45.91 0.2642 -56.57
5 -0.4968 -15.47 -0.3099 13.31 -2.7844 -31.60
6 0,0587 -17.57 0.9135 -46.47 -6.8299 372.00
7 -2.1509 -2.46 7.6277 -29.06
8 -1.7000 13.21 7.2997 -528.85
9 -7.4550 77.80
10 -5.0235 272.96
0,0008 0.0008 0.0022

aEq. (1). ~ (1) for x<0.98. CEq. (3) for x>0.98.

smoothing equations. Better fits of the results at a single temperature

are possible but have not been adopted in order to maintain a more
uniform treatment of the three systems.
i i i i 1 i i i

z~
0.008 0,004
x • xv
•
• 7 13

0.OO4 x
2n a o 0,002
T
"6 v 0 0 ~ x
E x
E o ~ v

9
.-'~ .......
o _ ~ o_. o
~ - -o - o--oo "~'-D.g <>_o 0
o x x

0 0 .... [3

-0.004 -0.002

-0.008 ~. ]-0.004
' 0.2' ' 014 ' 016 018 0.9 1.0

Fig. 1. Deviations, A Vm~ = VrnE(obs) - Vm~[Eq. (1)], for aqueous methanol mixtures
at 25oC, Poims:O, our results;f-I , Grolier et af.,t8> 4 points off scale:V, McGlashan
and WilliamsomI9) A , Mikhail and Kimel,(10)2 points off scale; O , Clifford and
Campbell, IlJ) 2 points off scale; X,'Gibson.(n) Curves: .... , +0.2% deviation. Note
that different uniform scales are used for both the abscissae and ordinales of points with x
values below and above 0.9.
798 Benson and Kiyohara

0.004 , , , , , , , ~ , 0.002

oq,
0.002 ............ ~176 o ~, 40.00l

. o Oo ~, ~O/oo-, [
E ." ~ o o ~.[x:) o ,, /

0 ~ _ _ _ _ o o-~O o--o-~ v'l-o---F---w~',lO

OC4.-~(~ 0v 0 V IV V 10 O0 ]

- 0.002 " " " - - . . . . - " " vv -0.001

0004 ~ ~ n , I i , J L -- " 0002

- " 0 0.2 0.4 0.6 0.8 0.9 1.6 "
36

Fig. 2. D e v i a t i o n s A VmE = VmE(ohs.) - VmE[Eq. (1)] for a q u e o u s e t h a n o l m i x t u r e s at

25~ Points: O . , o u r r e s u l t s ; ~ 7 , M i n o w a eta/.; o3) [ ] , O s b o r n e eta/. (14) C u r v e s : . . . . ,
+ 0 . 2 % d e v i a t i o n . N o t e that d i f f e r e n t u n i f o r m scales are u s e d for b o t h the abscissae a n d
o r d i n a t e s o f p o i n t s w i t h x v a l u e s below a n d a b o v e 0.9.

0.015 / , , , l , I E I ]

/
O.OLO /~ o _ _ ............ _ _

0 . 0 0 5 /F . - " " - n .
T o
o ~ A [] O~oo c) o ~
E
% 0 (% .
o ~ 0%0
o_(r) o

~ 0 80 oo
o
<3 o o zx -~
- 0.005 oo %'8 . o

-0.010

-0"0150
I I.
02
I I
0.4
I
~c
i
06
I
08
I. 0.9 1.0

Fig. 3. D e v i a t i o n s A VmE = VmE(Obs) - Vm E [Eq. (1) or Eq. (3)] for a q u e o u s l - p r o p a n o l

m i x t u r e s at 25oC. Points: O , o u r r e s u l t s ; A , M i k h a i l a n d Kimel;I15) r ' l C h u and
T h o m p s o n . ( 1 6 ) C u r v e s : . . . . , 4-1%. N o t e t h a t d i f f e r e n t u n i f o r m scales are u s e d for the
a b s c i s s a e o f p o i n t s w i t h x v a l u e s below a n d a b o v e 0.9.

Curves for the partial molar excess volume I/1E of water in the
three alcohols, and for the partial molar excess volume V2E of each
alcohol in water were calculated from the smoothing functions at 25~
Volumes of Water-Alcohol Mixtures 799

and are shown in Fig. 4. T h e curves for V~E are similar for the three
alcohols, with V~E negative except for mixtures dilute in alcohol. V2E is
negative throughout the composition range and the curves show a
characteristic m i n i m u m which, with increasing size of the alcohol
molecule, becomes deeper and shifts to higher alcohol dilutions. The
occurrence of such a m i n i m u m has been attributed to a balance
between the effects of interstitial solution of alcohol molecules with
accompanying e n h a n c e m e n t of an ice-like structure in the water, and a
breaking of this structure with increasing concentration of the
alcohol. (2,~9t
I I I I I I I I I

T
-8
I
- 2

-3
.t
""'"'"

...... Y ~'

\
'"

E
E
r

-4

-5

-61-

I I I I ~ I i
0 0.2 0.4 0.6 0.8 I.O

Fig. 4. Partial molar excess volumes o'f water Vie and of alcohol V2E at 25oC in aqueous
mixtures of methanol .... , e t h a n o l ~ and 1-propanol .....
T h e t e m p e r a t u r e variation of the excess v o l u m e s of aqueous
methanol mixtures is very different f r o m that of aqueous ethanol and
800 Benson and Kiyohara

aqueous 1-propanol mixtures. Thus, in the case of methanol, the five

isotherms are quite separate and ( 0 VmE/O T)p is negative for all
compositions. In contrast to this behavior, the sets of isotherms for
ethanol and for 1-propanol mixtures each have a point of intersection
where ( a vmE/a T)p changes sign. This difference in temperature
dependence is more evident when excess coefficients of thermal
expansion c~E are considered. Values of these were obtained from the
equations representing our results for VmE using the relation
o~E = [(O VmEIO T),- Vm~t~b~] + (1-,b),~;}l/Vm (4)
where Vm is the molar volume of the mixture, and a] and a~ are the
coefficients of thermal expansion for the pure components. Curves for
a E at 25~ are given in Fig. 5. The curve for the ethanol mixtures is in
excellent agreement with values of c~E derived f r o m - t h e earlier
investigations by Minowa et al. (~3) and by Osborne et al. (14) The
temperature dependence of densities for the methanol and the
1-propanol mixtures has been reported by Mikhail and Kimel. (l~
However, values of a E calculated from their results are widely scattered
and are not included in Fig. 5.
For aqueous methanol mixtures, the values of a E are negative
over the whole compostion range and the curve has two minima.
Apart from small negative loops in the water-rich region, the curves of
a E are positive for both ethanol and 1-propanol mixtures. The minima
of a E in the water-rich region occur near x = 0.92, 0.96 and 0.98 for
methanol, ethanol, and 1-propanol, 'respectively. With increasing
concentration of alcohol, the curves rise fairly steeply to their maxima
near x = 0.66, 0.77, and 0.89. The curve for methanol has a second
broader minimum centered around x = 0.24. The curve for
1-propanol shows traces of a shoulder below x = 0.5, and its overall
behavior is qualitatively similar to that of the aqueous tetrahydrofuran
mixtures studied previously. (6)
Partial molar excess expansibilities, defined by
Ei E = ( 0 viE/0 T) p (5)
were also computed at 25~ for each component. These results are
plotted in Fig. 6. The extrema and/or points of inflection which occur
near x = 0.8 in the curves for 1-propanol in this figure and also in Fig.
5 are probably spurious and attributable to the inadequacy of the
smoothing provided by Eq. (1). There have been several previous
investigations of the volume behavior of very dilute aqueous
n-alcohols. Table IV shows that our results for the partial molar excess
Volumes of Water-Alcohol Mixtures 801

0.2 , , t I I ~ 1 t I

o,,....''~ i
(3/ .." \
,,D....
a.o..., oc~
.o/. l

O.W ,"00
. .'"
..'~D i
.

o
T 9"" o / ~ I

." B" i

9"" k

X'

-O.I I i t I I I I N f
0 0.2 0.4 0.6 0.8 I.O
3C
Fig. 5. Excess thermal expansion coefficients a E [hq. (4)] at 2 5 ~ for aqueous mixtures
of methanol .... , e t h a n o l - - , and l-propanol ..... Points for ethanol: O , Minowa et aL;
(13) [ ] , Osborne et ak (141

volumes and expansibilities of the alcohols at infinite dilution, V2~,~ and

E2E,~ at 25~ are in reasonable agreement with values derived from
these earlier studies. (2~
In the water-rich region, E2z rises steeply with increasing alcohol
concentration and changes from negative to positive values, reaching a
maximum near x - = 0.85, 0.90, and 0.95 for methanol, ethanol, and
1-propanol, respectively. At present the molecular significance of this
maximum is not clear but it appears to be attributable to some
structural transition taking place in the mixture. Positive values of E2E
are often interpreted as evidence of a breaking of the water structure
by the solute, (2) and on this basis the present work indicates that the
degree of disruption depends noticeably on the relative sizes of the
polar and apolar parts of the n-alcohol molecule.
802 Benson and Kiyohara

8O I I I I I I I I I

"7
40
f
E
T Ee Ee
Y
20 ~
E
0
bJ.-
bA

0
J ~t
d

-20

-40

I, I I I I i I I I I I
0 0.2 0.4 0.6 0.8 1.0

Fig. 6. Partial molar excess thermal expansibilities of water E1E and of alcohol
E2 E al 25oC for aqueous mixtures of methanol .... , e t h a n o l - - , and 1-propanol .....

Table IV. Partial Molar Excess Properties of Alcohol in Infinitely

Dilute Aqueous n-Alcohol Mixtures at 25~

n-Alcohol v2E'~ "1) E2E'0(cm3-kK|-mol-1)

Obs. Ref.20 Ref.21 Ref.22 Obs. Ref.20 Ref.21 Ref.22

MeOH -2,53 -2.62 -2.49 -2.64 -36.0 -36 -38 -38

EtOH -3.52 -3.61 -3.45 -3.65 -48.2 -56 -54 -43
I-PrOH -4.22 -4.52 -4.25 -4.87 -42.8 -35 -48 -50
Volumes of Water-Alcohol Mixtures 803

Near the middle of the composition range, the values of E~E and
E~E are nearly constant. This is reminiscent of the partial molar excess
enthalpy curves reported for aqueous ethanol mixtures. (23) It has been
suggested that this behavior results from an equilibrium between
microphases consisting of structured water clusters and a random
mixture of water and alcohol molecules. (23) However, it appears that
this argument cannot be used to rationalize the volume behavior of
aqueous n-alcohol mixtures since, apart from the constancy of the
values of E~E, there is no evidence of an approximately linear variation
of V~E with x and the values of I/1 z and V2E are not constant over the
corresponding range of compositions.

ACKNOWLEDGMENTS

The authors are indebted to Mr. A.S. Secco for some of the
density measurements, to Dr. J.-L. Fortier (University of Sherbrooke)
for the Karl Fischer analyses, and to Mr. P. J. D'Arcy and Mr. C. J.
Halpin for other technical assistance. We also thank Dr. Y. P. Handa
for helpful discussions of the work. This paper is issued as NRCC No.
18868.

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