c. HOWARDSHOMATE AND OSCAR A. COOK
21.10
Summary
1. The ultraviolet absorption spectra of 2thiouracil, 2,4-dithiouracil, 4-thiouracil, %thiothymine, 2,4-dithiothymine and 4-thiothymine are given at I;H values 1, 7 and 11.
[CONTRIBUTION
FROM THE
Vol. 68
2. Comparison is made between the spectra of these thio derivatives with the spectra of uracil and thymine and the anomalods position of the absorption bands of 4-thiouracil and 4-thiothymine is discussed. TUCKAHOE, N. Y.
RECEIVED JUNE 19, 1946
PACIFICEXPERIMENT STATION, BUREAUOF MINES,UNITEDSTATES DEPARTMENT OF
THE
INTERIOR]
Low-Temperature Heat Capacities and High-Temperature Heat Contents of Al,03~3H,0and Al,03*H,0 BY C. HOWARD SHOMATE~ AND OSCAR A. COOE;~ One of the recent programs of the Pacific Experiment Station of the Bureau of Mines has been the measurement of thermodynamic properties of aluminum compounds of interest in certain processes for extracting alumina from clay and alunite. Several previous papers3 on this subject have been published. The present paper, the concluding member of this series, presents lowtemperature heat-capacity and high-temperature heat-content data for two crystalline hydrates of alumina. Materials The tri-hydrate of alumina was prepared in this Laboratory by A. E. Salo4 by dissolving aluminum wire in 0.2 N potassium hydroxide. The precipitated crystals of A1203. 3H20 were washed with 4 AThydrochloric acid t o remove iron resulting from the original impurity in the aluminum wire, washed finally with distilled water, and dried a t 140 '. Analysis was made by fusion with sodium bisulfate and precipitation by the 8-hydroxyquinoline method. Analysis gave 65.62% aluminum oxide (theoretical 05.35y0). The sample used in the low-temperature heat capacity measurements weighed 86.36 g., and the hightemperature heat content sample weighed 4.129 g. The mono-hydrate of alumina was prepared by heating the tri-hydrate a t 220" for three days. The aluminum oxide content was found to be 3% too high, so the required amount of water was added and the mixture stabilized by heating a t 80' for sixteen hours in an evacuated flask. Since the product was not readily fusible in sodium bisulfate nor satisfactorily soluble in any ordinary reagent, analysis was made by iguiting to aluminum oxide in a platinum crucible over an oxygen-rxatural gas flame. Analysis gave 85.00pl, aluminum oxide (theoretical 84.9094,). A 112.30-g. sample was used in the low-temperature measurements, and a 4.228-g. sample for the measurements at high temperatures. X-Ray examinations showed the tri-hydrate to have the structure of gibbsite (A1103.3H20), and the mono-hydrate a structure similar to bayerite (A120,.3H,O), differing from the latter principally i n the intensities of the lilies.
Low-Temperature Heat Capacities The method and apparatus used in the ldw temperature heat-capacity measurements were (1) Published by permssion of t h e Director, Bureau of Mines, U. S. Department of t h e Interior. N o t copyrighted. (2) Chemist, Pacific Experiment Station, Bureau of Mines. (3) (a) Shom,ite a n d S a y l o r , T H I S Jlinea.
described p r e v i o ~ s l y . ~The ~ ~ experimental results, expressed in defined calories (1 calorie = 4.1833 int. joules},' are listed in Table I and shown graphically in Fig. 1. The values of the heat capacities a t 298.16'K., read from a smooth curve through the experimental points, are also included in Table I. The molecular weights are in accordance with the 1941 International Atomic Weights. TABLE I MOLALHEATCAPACITIES AlnOa.3HnO
Mol. wt.,155.99 C p , cal./deg.
T,O K . 52.8 56.9 61.1 65.2 69.8 74.0 78.4 85.3 94.8 104.7 115.3 125.3 135.1 145.4 155.3 165.5 175.7 185.7 196.0 205.9 216.2 226.2 235.8 246.2 256.2 266.3 276.3 286.3 296.5 (298.16)
3.213 3.708 4.259 4.816 5.506
6.lG4 6.854 8.002 9.677 11.54 13.57 15.51 17.47 19.50 21.39 23.38 25.35 27.15 28.97 30.72 32.55 34.09 35.55 37.19 38.72 40.17 41.63 42.94 44.27 144,49)
AltOs.Ha0 Mol. wt., 119.96 T,O K . Cp,cal./deg.
52.7 56.9 61.0 65.2 69.3 73.8 78.3 84.8 94.7 104.5 115.1 125.3 135.0 145.6 155.4 165.5
175,4 185.G 195,s 205.9 216.2 226.2 235.9 216.2 256.4 266.1 276.2 286.2 296.4 (298 16)
2.179 2.528 2.914 3.307 3.733 4.216 4.709 5.441 6.630 7.865 9.228 10.58 11.92 13.31 14.62 15.98 17.32 18.66 20 ou 21.32 22.57 23.74 24.83 25.99 27.14 28.26 29.27 30.17 31.13 (31.37
( 5 ) Kelley. THISJ O U R N A L , 63, 1137 (1941). (6) Shomate a n d Kelley, ibid., 66, 1400 (19441. ( 7 ) hIueller and Rossini, A m . J. Physics, 12, 1 (1044).
I
Nov., 1946
HEATCAPACITIES AND HEATCONTENTS OF HYDRATED ALUMINUM OXIDES
2141
Table I1 summarizes the entropy calculations for the two hydrates.
High-Temperature Heat Contents The heat-content measurements were made by the “drop” method. The experimental procedure and apparatus have been described previously.8 During the measurements the samples were contained in platinum-rhodium alloy capsules, the heat contents of which had been determined separately. After being filled with sample, the capTABLEI11 MOLAL HEAT CONTENTS ABOVE 298.16’K. AlnOs.3HzO
Mol. wt.,155.99 H T - Hzo1.16,cal.
T,OK. 322.2 323.0 349.1 373.2 423.5
0
100 200 Temp., OK. Fig. l.-lMolal heat capacities.
300
All weights were corrected to vacuum using the following densities: A1203.3H20, 2.43; and A1203. HPO,2.5;;g./cc ., respectively. These values were determined in this Laboratory by A. E. sal^.^ The two hydrates exhibited normal behavior, there being no thermal anomalies in the temperature range studied.
Entropies at 298.16OK. Evaluation of the entropies a t 298.1G’K. is obtained by numerical integration of a plot of Cp against log T. This necessitates the extrapolation of the heat-capacity curve from the temperature of the lowest measurement down to absolute zero of temperature. It was found that the following function sums adequately represent (within 1%) all the measured heat capacities
The symbols D and E denote, respectively, Debye ant1 Einstein functions. These functions were used for extrapolating the heat-capacity curves to 0°K. (broken lines in Fig. 1). TABLE I1 ENTROPIES AT 298.1G’K. (E.U./MOLE) AliO13Hz0
O-Fi2 O O O I ; . (extrapolated) 1 -IO 5 2 . 0 - 2 9 8 lf.i°K, (iiicazurecl) 32 11
33.51
A1203 Hz0
0 94 22 21
0.1 23.15 * 0 . 1
=t
1056 1095 2322 3594 6312
AIzO*.HzO Mol. wt.,119.96 H T - Hzon.is, cal.
T,‘IC. 321.7 341.0 366.2 416.2 445.4 473.0 500.4 520.1
688 1255 1969 3669 4690 5746 6901 7914
sules were evacuated of air, filled with helium, and quickly sealed. The results are listed in Table 111 and shown graphically in Fig. 2. X,O( )I I
6,000 v;
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$ 4,OOC I
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