T H E SPECIFIC HEATS OF F I V E P U R E ORGAKIC LIQCIDS AXD OF ETHYL ALCOHOL-IT'ATER MIXTURES* BY FRASCIS E . BLACET, PHILIP A. LEIGHTOS AND EDWARD P. BARTLETT
1. Introduction Apparatus and Method Although many measurements of the specific heats of such organic liquids as ethyl alcohol and aniline have been reported, few of these have been made by methods which permit of measurement over small temperature intervals. At elevated temperatures in particular, the applications of methods of calorimetry which permit measurements over a continuous chain of small temperature intervals are singularly few. Villiams and F. Daniels' have made measurements over 5' intervals in the range 30"-80" on fifteen pure organic liquids. Parks? and collaborators, employing the Xernst method, have made similar measurements at temperatures up to 30' on a number of liquids. In the present work, an adiabatic calorimeter with a capacity of I j o cc. was employed (Fig. I ) , in which heat was added to the liquid a t a constant rate from an electrical heating coil, and the ttnae interoal between each fivedegree rise, and in some cases between each two-degree rise in temperature was measured. In this way an unbroken chain of specific heat readings could be obtained, without the necessity of waiting for temperature equilibrium before each reading. The calorimeter was constructed for use up to 300°C. KO solder was employed. The containers were built of thin copper, and all joints were either welded or held by screws. The lid was made tight with an asbestosgraphite gasket. The inner calorimeter was equipped with a single stirrer, provided with a long close fitting bearing to reduce evaporation error, while the surrounding adiabatic bath had three stirrers placed symmetrically around the inner container. For heating units, a single coil of nichrome, completely surrounding the stirrer, served for the inner liquid, and three coils, symmetrically placed between the stirrers, were used in the outer bath. One degree per minute was chosen as the standard rate of temperature rise. The stirrers were all driven by a single cord from a constant-speed motor. Experiments with various speeds of stirring resulted in 2 . 5 revolutions per second being chosen as the optimum rate. Temperatures were read to 0.01' by means of thermometers calibrated by the U. S. Bureau of Standards. Two ranges of thermometers, 0-100' C. and 100-200' C. were employed. By using the
* Contribution from the Chemistry Laboratories of Pomona College and of Stanford University. J. Am. Chem. Soc., 46, 903, 1569 (1924). * J. Am. Chem. Soc., 47, 338, 2089 (1925); 48, 1506, 2788 (1926); 51, 1969 (1929); 52, 1032, I547 (1930).
1936
FRANCIS E. BLACET, PHILIP A. LEIGHTON A N D EDWARD P . BARTLETT
FIG.I Complete Calorimeter
o 5zo 0 460
0 u.70
0 400
I
0
,
!
ZO
40
60
I
80
GRAPHI Specific Heat of Ethyl Benzene
I (00
SPECIFIC HEATS OF LIQUIDS AND AQUEOUS ALCOHOL
I937
method of constant heat input and its corresponding constant rate of temperature rise, it was quite easy to keep the inner and outer temperatures equal. K h e n dissimilar liquids, e. g., uFater and kerosene, were used in the inner and outer containers, an interesting effect was observed. For example, the calorimeter constant, or correction for heat capacity of the calorimeter itself, was increased 10% at 30' C., and 2 5 7 0 at 90' C., by using kerosene instead of water in the adiabatic bath, water being used in the calorimeter proper in both cases. This effect was no doubt due to the greater heat-carrying capacity (a function of specific heat, density, and thermal conductivity) of water as compared to kerosene. When using water in the inner and kerosene in the outer compartments, the water would heat more than its share of the calorimeter, due to more rapid transfer of heat from coil to walls, resulting in a 10% to 2 j% error in the calorimeter constant. For this reason, the same liquid, or a liquid with specific heat per cc. and thermal conductivity very nearly equal to that of the liquid being measured, was always placed in the surrounding adiabatic compartment. Every possible source of error known to us was carefully checked. Thermometer calibrations were corrected for emergent stem; voltmeter and ammeter were calibrated over their entire scales; and the errors due to heat of stirring, evaporation, variation in thermal head, inaccuracy in calibration, inaccuracy in reading instruments, etc., were investigated. As a result, we believe the maximum error to be expected in any specific-heat reading is about 3%.
Specific Heats of Ethyl Benzene, Diphenyl Methane, Aniline, and Naphthalene n . Illaterials Ethyl Benzene: Refluxed over mercury, shaken with conc. HnS04,dilute S a O H , and water, allowed to stand 30 days over P20j. B. P. = 1 3 5 . 5 ~136.5'; Kg = 1.49695; Nr - so= 0.01531. s p . gr. 0.8904. It was necessary 2.
to use the large boiling range indicated in order to obtain enough material to fill the calorimeter.
Diphenyl -If ethane: purified in same manner as ethyl benzene, except dilute H 8 0 a used instead of concentrated. B. P. = 261~-262~ C., Xg = 1.5;390;
S r - S,
= 0.0~079.
Anzlzne: fractionated from Baker's aniline. B. P. = 182.0'~ Sp. gr. = 1.02; SnphthaZPne: Redistilled from c.p. naphthalene. 51.P. = 80.o'~ B. P. = 2 1 7 . 9 ~Sp. ~ gr. =
1.110.
b. Results The specific heats obtained are reproduced in Table I and on the accompanying graphs. Each set of figures and each graph represents the mean of from two to four individual series of determinations.
1938
FRANCIS E. BLACET, PHILIP A. LEIGHTON A S D EDWARD P . BARTLETT
GR.APHz Cooling Curve for Ethyl Benzene
r ,4980 1.49 GO
I . 4940
GRWH3 Index of Refraction for Ethyl Benzene
Wherever possible, the graphs also include the results of other investigators, which are marked by letters denoting the references as given below3 The comparison of specific heat curves for ethyl benzene is of especial interest (Graph I ) . Wlliams and F. Daniels‘ observed a marked irregularity 3
On Ethul h’ei~zene
4
B-L-B,-this aper. H-P-D,-HufPman, Parks and A . C. Daniels: J. Am. Chem. Soc., 52, 1547 (1929). W-D,-Williams and F. Daniels: J. Am. Chem. Soc., 46, 903, I 569 (1924). O n Aniline B-L-B,-this paper. B,-Bartoli: Nuovo Cimento, (4) 2, 347 (1895). G,-Griffiths: Phil. Mag., (s), 39, 47, 143 (1895). L,-Louguinine: Ann. Chim. Phys., (7) 27, Ioj (1902). P,-Penot: Arch. sei. phys., (3) 32, 14j (1894). Pe,-Petit: Ann. Chim. Phvs., (6) 18, 145 (1889). S,-Schiff: Z.physik. Chem., 1, ,376,(1887). S,-Schlamp: Ber. Ges. Xaturw. Heilk., 31, 100 (1895) T,-Timofijew: Dissertation, Kiew (19oj). LOC.cit.
SPECIFIC HEATS O F LIQUIDS AND AQEEOUS ALCOHOL
I939
TABLE I Specific Heats of Organic Liquids Temp. C"
Ethyl Benzene
I7
0.396 .395 ,400
I9
,405
I3 15
21
,411
23
.4I8 ,420 ,426
25 27
Diphenyl Methane
Aniline
. 4 22
29 30 31 33 35
.430
0.503
40
'435
,507
45
'
50
,450
'
55 60 65 70
,452
,520
,462 ,471
,526
,473 ,433
,495 ,498 ,496
.532 ,533 ,535 ,536 ,538
,510
'545
75
80 85 90 95 104.8 108.8 113.8 118.9 124.0 129.2 134.4 '39.6 144.8 150.0
155.3 160.4 165.6 170.9 176.1 181.6 187.I 192.7
,424
0 .j00
-
,426 ,426
444
,512
515
,528
. j j2 ,559
,564
.5 7 5 .58I ,601 ,627
.66j
Naphthalene
1940 FRANCIS E. BLACET, PHILIP A. LEIGHTON AND EDWARD P. BARTLETT
in the specific heat between zoo and 30' C. Huffman, Parks and A. C. Daniels5 on the other hand obtained a smooth curve from the melting point to 32' C. Our values show a tendency toward the same variation as observed by Williams and Daniels, although less marked. Some experiments we made on benzene show a tendency toward irregularity in almost the same temperature range (z5'-35' C. for benzene, 2oo-3o0 for ethyl benzene). No such irregularity was found for any of the other liquids examined.
GRAPH4 Specific Heat of Aniline
GRAPHj Specific Heats of Diphenyl Methane and Naphthalene
Williams and Daniels found no variation in the density or in the vapor pressure of ethyl benzene throughout the temperature range in question; we find no variations in the cooling curve, (Graph 2). There is possibly a variation in the index of refraction-temperature curve in the region 26'-28', (Graph 3 . ) but it is scarcely beyond the limit of accuracy of the refractometer used. The specific heat curve for aniline, (Graph 4), shows several marked changes in slope. The rapid rise beyond I I 5' is probably due to a chemical Huflrnan, Parks and A. C. Daniels: J. Am. Chern. Soc., 52, 1547 (1929).
SPECIFIC HEATS OF LIQVIDS AND AQUEOUS ALCOHOL
1941
decomposition of the aniline, induced by the metal walls of the container or by electrolysis from the heating coil. When heated above this temperature in the calorimeter the aniline rapidly turned black. The specific heats of diphenyl methane and of naphthalene, (Graph s), are straight line functions of the temperature. Indeed, they are directly proportional to the absolute temperature throughout the range measured. Diphenyl methane, Sp. Heat = 1 . 3 1 2 T. Naphthalene, Sp. Heat = 1.289 T.
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GRAPH6 Specific Heats of Ethyl Alcohol-Water Mixtures. Weight-percentage of alcohol in the mixtures are given.
3. Specific Heats of Ethyl Alcohol and of Ethyl Alcohol-Water Mixtures
Isolated measurements of the specific heats of various ethyl alcohol-water mixtures have been reported for sixty years.6 Bose made the first attempt to correlate change in specific heat with relative concentrations. His measurements showed that the specific heats of alcohol-water mixtures are higher than would be expected for an ideal or perfect mixture. The amount of this variation changed with the temperature but the way in which it changed was not clear. Bose correlated this variation in specific heats with the heat of mixing and its temperature coefficient. Doroshevskii and Rakovskii, as well as Kolosovskii, have derived empirical formulae for the specific heats of alcohol-water mixtures. These formulae, however, fail to take account of the change in specific heat with temperature. 6Schuller: Poeg. Ann., V, 116, 192 (1871); Blumcke: W e d . Ann., 25, 154 (188j); Magie: Phys. Rev., 9, 65 (18 9 ) ; Zettermann; Bose: 2. physik. Chern., 58, 585 (1907); Doroshevskii and Rakovskii: Russ. Phys. Chem. Soc., 40, 860 (1908); Kolosovskii: 48, 84 (1916).
f.
1942 FRANCIS E. BLACET, PHILIP A. LEIGHTON AND EDWARD P. BARTLETT
The relations between the three variables] specific heat, temperature] and concentration can in fact only be obtained by measuring a number of concentrations over a series of short temperature intervals. We have made such measurements. Absolute ethyl alcohol was prepared by the usual method of distillation after standing 30 days over pure calcium oxide. The various mixtures were made by diluting this alcohol with pure water. The specific heats found are given in Table I1 and on Graph 6 . As before, each figure in the tables and each point on the curves represents the average of several independent determinations. Our values for the specific heat of pure ethyl alcohol are compared with others found in the literature on Graph 7.*
GRAPH 7 Specific Heat of Ethyl Alcohol
On Graph 8, the specific heat is plotted against relative concentration:for two temperatures. The same bow-shaped curves as observed by Bose are obtained. The curve a t 30' is flattened on the side of high alcohol concentration. As the temperature increases, this side builds up until at 70' the curve is almost a perfect bow shape. This relation is emphasized on Graph 9, where the departure of the specific heats from those of an ideal mixture are plotted against relative concentration.
* References
for pure ethyl alcohol, corresponding to initials on Graph 7. B,-Bose: Z. physik. Chem., 58, 585 (1907). Bl,-Blhmcke: Wied. Ann. 25, I j4 (188j). B-L-B,-Blacet, Leighton and Bartlett: this paper. D,-DeHeen and Deruyts: Bull. de Belg., (3) 15, 168 (1888). D-R,-Doroshevskii and Rakovskii: J. RUM.Phys. Chem. SOC.,40, 860 (1908). K,-Kelley: J. Am. Chem. SOC.,51, 779 (1929). L,-Louguinine: Ann. Chim. Phys., (7) 13, 289 (1898). P,-Parks: J. Am. Chem. Soc., 47, 338 (1925). R,-Regnault: Mem. de I'Acad., 26, 262 (1862). S,-Schuller: Pogg. Ann., Erg V, 116, 192 (1871). Su,-Sutherland: Phil. Mag., ( 5 ) 26, 298 (1888). T,-Timofejew: Dissertation, Kiew (1905). W-D,-Williams and Daniels: J. Am. Chem. SOC.,46,903,I569 (1924);47, I490 (1925).
SPECIFIC HEATS OF LIQUIDS AND AQUEOUS ALCOHOL
I943
TABLE I1 Specific Heats of Ethyl Alcohol-Water Mixtures Temp. 30 35 40
45
50 55
I O 0 70
0.603 ,614 ,633 ,653 ,669
Per Cent Alcohol 95% 75% 0.668 0.796 ,683 ,815 ,698 '834
,716 '734
,688
,753
60
.joj
'771
65 70 75
'723 ' I33
--
,792 ,828
-
25% I ,051
,925 ,946
,855 .8j8
,955
,893 904
,975 ' 983 ,995
1.053 1,055 I , 060 I . 062 I ,065 I ,066 I ,066
I ,008 1.013
1.074 I ,074
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P GRAPH8 Relations of Concentration and Temperature in the Specific Heats of Ethyl Alcohol-Water Mixtures.
GRAPH9 Variationsin the Specific Heats of Ethvl rllcohol-Water Mixture? from the Ideal Mixture Relationship.
At 30°, the maximum variation is found for 3 0 7 0 alcohol. The corresponding mole fractions are alcohol 0.17, water 0.83. As the temperature rises, the maximum moves regularly in the direction of higher alcohol concentration until a t 70" it reaches 55% alcohol. For this concentration the mole fractions are alcohol 0.33, water 0.67.
Summary The specific heats of five pure organic liquids and of ethyl alcohol-water mixtures have been measured over a range of temperatures. Irregularities in the specific heat of ethyl benzene, and the departure of the specific heats of alcohol-water mixtures from those of ideal mixtures, are discussed.
