as the reference state for elemental sulfur for temperatures other than 298.16"K. The computed values are presented in Table VIII. Acknowledgments.-The authors wish to thank Dr. J. Rud Nielsen, of the Physics Department, University of Oklahoma, Korman, Oklahoma, and Air. T. C,. Burke, of the Phvqics Department,
[COUTRIRUTIDY S O .
28
FROM THE
THERMOnVShMICS
Carbide and Carbon Chemicals Division, Oak Ridge, Tennessee, for making available spectroscopic data which were essential to this investigation. The assistance Of J I r . Robert Robinson in Some of the experimental measurements is gratefully acknowledged. RARTLESVILLE,
OKLAHOMA
L.%BoRA4TOKV,PETKOLEUhl E Y P E R I M E Y T STATION, BURESU O F M I N E S ]
Thermodynamic Properties of Furan BY G. €3. GUTHRIE, JR.,
n.W.SCOTT,W. N. HUBBARD,C. KATZ,J. P. MCCULLOUGH, M. E. GROSS, E;. D. WILLIAMSON AND GUYWADDINGTON RECEIVED APRIL 3, 1952
A sample of furan was purified and used for calorimetric studies and for measurement of vapor pressure, density, refractive index, infrared spectrum (2-15~) and mass spectrum. The heat of formation of liquid furan (-4Hf = 14.90 kcal. mole-') mas derived from heat of combustion measurements. Low temperature thermal studies included measurement of the heat capacity of the solid, transition temperature (15O.O0K.),heat of transition (489.2 cal. mole-'), triple point (187.55 K.), heat of fusion (908.8 cal. mole-') and heat capacity of the liquid. The entropy of the liquid a t 298.16"K., calculated from these data is 42.22 cal. deg.-' mole-'. The observed vapor pressures between 2 and 62 are represented by the equation loglop (mm.) = 6.97523 - 1060.851/(1 227.740). The heat of vaporization a t the normal boiling point (31.36") is 6474 cal. mole-'. The vapor heat capacity, measured a t five temperatures between 317 and 488"K., is given by the equation C,O = -7.55 9.352 X 9.352 X 1 0 F T - 5.287 X T 2cal. deg.-l mole-'. The equation B = -279 - 22.6 exp(950/T) cc. mole-' was derived for the second virial coefficient from calorimetric data. A vibrational assignment which was partly empirical was made and used with molecular structure data t o compute thermodynamic functions of the ideal gas to 1500 OK. The heat, free energy and equilibrium constant of formation a t temperatures to 1500" were calculated using appropriate calorimetric data and thermodynamic functions.
+
+
An investigation of the thermodynamic properties of furan was included in the research program of this Laboratory following a recent study of its sulfur analog, thiophene.' Derivatives of furan are used widely in the petroleum industry and are important items in the chemical trade. This investigation, in addition to supplying thermodynamic data for furan itself, has provided fundamental informatioil which will be needed for future studies of the various derivatives of furan. The several phases of this investigation, in the order of their presentation in this paper, were: ( I ) purification of the material and determination of the infrared spectrum of the liquid and of some of its physical properties including the triple point, density and refractive index; (2) measurement of the vapor pressure as a function of temperature; (3) determination of the heat of combustion and heat of formation; (4) measurement of the heat capacity of the solid and liquid and the heats of transition and fusion; ( 3 ) measurement of the heat of vaporization and the vapor heat capacity; (6) calculation of the entropy of the liquid and of the ideal gas from the appropriate experimental data; and ('7) calculation of the thermodynamic functions and the heat, free energy and equilibrium constant of formation of the ideal gas a t selected temperatures from molecular structure, spectroscopic and calorimetric data. Units and Conversion Factors.-In this paper the defined calorie (1 cal = 4.18 40 abs. j.) is used throughout for the unit of energy. Celsius temperatures are converted to Kelvin temperatures by adding 273.16". The molecular weight of furan calccilntcd from the 1939 atomic weights is 68.072. (1) C. Waddington. J. W. Knowlton, D. W. Scott, G. D. Oliver, S. Todd, W. N. Hubbard, J. C . Smith a n d FI, SI. Huffman, THIS JOI.KNL. 71,7',27 ( 1 9 i O ) .
S.
The Material and Its Physical Properties Purification and Purity.-About 1.2 1. of technical furan was distilled through a 70-plate column packed with steel helices. An atmosphere of nitrogen was maintained in the still a t all times, and an inhibitor (hydroquinone) mas added t o each fraction when it was removed. Two 70-ml. heart cuts, samples A and B , were used for low-temperature and vapor pressure measurements, respectively, and portions of both samples were used for determining the heat of combustion. Later these two samples were combined for the determinations of the density, refractive index and infrared spectrum. Several other cuts, totaling about 300 ml., were combined into a third sample ( C ) , which was used for the heat of vaporization and vapor heat capacity measurements. Each sample of furan was separated from the inhibitor and dried by a bulb-to-bulb distillation under its own vapor pressure in which the vapors passed over anhydrous magnesium perchlorate. The samples were stored in sealed ampoules under their own vapor pressure. I n the course of the low temperature thermal measurements, the purity of sample A was determined to be 99.98 =t 0.01 mole %.* The purity of sample B was not determined quantitatively. Since the boiling and condensation temperatures observed in the vapor pressure measurements differed by only 2 millidegrees a t the normal boiling point, it is evident that sample B did not contain enough impurity of different volatility to have any significant effect on the vapor pressure measurements. The heat of combustion of this sample was indistinguishable from that of sample A. Since this measurement is sensitive to about 0.05 mole 70 of Cs-hydrocarbons (the most probable impurities), it is believed that sample B was more than 99.9 mole 700pure. The mass spectra of samples A and C were determined.3 Isopentane (0.01 mole %) and a trace of an unidentified impurity (peak a t 85) were found in sample A. Sample C showed 0.04 mole % isopentane and a somewhat larger trace of the same unidentified impurity. This analysis sug(2) This value was calculated with the assumptions of ideal solutions and liquid-soluble, solid-insoluble impurities and is somewhat arbitrary since there is evidence t h a t some of the impurities were solid-soluble. See discussion of the melting point. (3) A mass spectrum, obtained from this s t u d y and corrected for impurities. has been published in the "Catalog of hlass Spectra," American Petroleum Institute Research Project 44, Carnegie Institute ,,f ' l ' e c h ~ u h g y . Pittshiirgh, r:, , 10.71, S O . A*:,
THERMODYNAMIC PROPERTIES OF FURAN
Sept. 20, 1952
gests that sample C contains about four times the impurity of sample A and is about 99.9 mole % pure. Melting Point.-The triple point of furan was determined as part of the low temperature measurements. The equilibrium temperatures, observed as a function of the fraction melted, are given in Table I. The cryoscopic constant,
2-\l
TABLE I MELTINGPOINTOF FURAN = 0.0130AT: triple point = 187.55 =t 0.05’K.; impurity
.V:
= 0.019 =t 0.010 mole
Me1ted,
Tobad.,
70
12.94 25.16 49.81 70.01 90.21 100.00 Pure
%
O K .
7.731 3.974 2.008 1.428 1,109 1.000 0.000
187.4407 .4913 .5205 .5282 .5348
.... ....
187.4360 ,4915 .5206 .5291 .5339 .5355 .550
AHfu./RT2T.p. = 0.0130 deg.+, was calculated from the heat of fusion (see below). If the impurities are all liquidsoluble, solid-insoluble and form ideal solutions in furan, then TT,I,,- T = A T = A72*/0.0130F (1) where N2* is the mole fraction of impurities in the entire sample and F is the fraction of furan melted.‘ If the equilibrium temperatures are plotted as a function of 1/F, the impurity can be calculated from the slope, and the triple point can be obtained by extrapolation to 1/F = 0. This analysis is not strictly applicable in the present case where T is not a linear function of l/F. The apparent impurity (corresponding to the slope) in different regions varies from 0.027 mole % (between 90 and 70% melted) through 0.019 mole % (between 50 and 25% melted) to 0.017 mole % estimated from premelting. This trend probably is due to the formation of solid solutions. Density.--The density of furan was determined a t three temperatures in a 25-cc. Bingham pycnometer. The values obtained were t , OC.
&‘g. cc.-1
10 0.95144
15 0.94467
20 0.93781
These densities are believed to be accurate to &lo-’ g. cc.-l, while the internal precision is f5 X g. cc.-I. The coefficient of expansion a t 15’ is 1.44 3= 0.01 X 10-3 deg.-’. Refractive Index.-The index of refraction of furan a t 20’ was measured a t six wave lengths by the proposed ASTM m e t h ~ d using ,~ a Bausch & Lomb precision refractometer. The errors of measurements should not exceed &6 X 10-6. The values of the refractive index found are A,
A.
6 5 6 2 . 8 5892.6
5460.7 5015.7
4861.3 4358.3
N x Z o 1.41822 1.42140 1.62418 1.42791 1.42954 1.43619 These data are represented between 6562.8 and 4358.3 A. within = t 2 X 10-5 by the empirical equation S X = ~ 1.40501 ~ 0.0047922/(A - 0.125601)’.6 (2) derived by the method of Forziati.6 Infrared Spectrum.--The infrared spectrum of furan was determined for the liquid state between 2 and 15 w. The spectrogram obtained in this study has been included in reference 7. The infrared data for liquid furan that are pertinent to the calculation of the thermodynamic functions are presented in a subsequent section (Table VII).
+
(4) S. S. Todd, G. D. Oliver and H. M. Huffrnan. THISJOURNAL, 69, 1619 (1947). (5) ASTM proposed method of measurement of refractive index and refractive dispersion of hydrocarbon liquids. “ASTM Standards on Petroleum Products and Lubricants,” American Society of Testing Materials, Philadelphia, Pa., 1960, Appendix IV, p. G86. ( 6 ) A. F. Forziati, J. Research Nafl. Bur. Standards, 44, 373 (1950). (7) “Catalog of Infrared Spectral Data,” American Petroleum Institute Research Project 4 4 , Carnegio Institute of Technology, Pittsburgh, Pa., 1952, Serial KO.1277.
4663
Vapor Pressure and Boiling Point The vapor pressure of furan was measured from 2 to 62’ by comparative ebulliometry. The method and apparatus have been described previous1y.l The results of the meas-
TABLE I1 VAPORPRESSURE OF FURAN,EBULLI OMETRIC METHOD Boiling point, “C. Water Furan
70. 000 75 80 85 90 95 100 105 ’ 110 115 120 125 130
2.552 7.267 12.018 16.797 21.614 26.469 31.357 36.279 41.241 46.232 51.265 56.329 61.430
Pressure, mm. Obsd. Calcd. (eq. 3)
’
233.72 289.13 355.22 433.56 525.86 633.99. 760.00 906.06 1074.6 1268.0 1489.1 1740.8 2026.0
233.71 289.13 355.27 433.54 525.81 634.00 760.00 906.02 1074.7 1268.0 1489.2 1740.8 2025.9
urements are presented in Table 11. An Antoine equation was fitted to the data, using the least squares treatment of Willingham, et al.,8 and giving all points equal weight. The equation obtained is
+
loglo = 6.97523 - 1060.85l/(t 227.740) (3) 1-alues of the vapor pressure calculated from this equation are included in Table I1 for comparison with the observed data. The normal b:iling point of furan calculated from this equation is 31.36 . Heat of Combustion and Heat of Formation The heat of combustion of furan a t 25’ was determined, using a bomb calorimeter of the “constant temperature environment” type. This datum has been used to calculate the standard heat of formation. The apparatus, conditions and techniques have been described previously.* The bomb used in these combustions was made of illium and sealed with a fine-gold gasket. The volume of the bomb was 0.374 1. When many of the experiments showed evidence of incomplete combustion, a platinum baffle was suspended in the crucible over the ampoule to prevent splattering and to localize the combustion zone.1° This technique was used in two experiments and probably was beneficial. Calibration.-The energy equivalent of the system, SB, was determined from combustions of NBS standard sample 39f (benzoic acid), which has a certified value of 26.4338 abs. kj. per gram mass for its isothermal heat of combustion under standard conditions. l1 This value has been corrected to 26.4306 abs. kj. because the conditions of this investigation were not quite those of the standard bomb process. During the first part of this investigation, the energy equivalent was 3192.812 cal. deg.-l. After making minor repairs the energy equivalent was redetermined and found to be 3193.713cal. deg.-l. The results of the combustion experiments refer to the isothermal process a t 25” and true mass. (8) C. B. Willingham, W. J . Taylor, J. hi. Pignocco and F. D. Rossini, J. Research N a f l . Bur. Sfandards, 36, 219 (1945). (9) U’.S. Hubbard, J. W. Knowlton and H. M. Huffman, THIS TO, 3256 (1048). JOURNAL, (10) This baffle is a modification of Sunner’s “top” IS. Sunner, Dissertation, University of Lund, 1Y49, “Studies in Combustiun Calorimetry Applied to Organo-Sulfur Compounds,” Carl Bloms Boktryckeri, Lund, Sweden, 1949, pp. 45-491 and is used regularly in this Laboratory in the combustion of sulfur compounds. Cf. also, S. Kaarsernaker, Dissertation, Vrije Universiteit, 1951, D. B. Centen’s Uitgevers-Mattschappij N. V., Amsterdam, 1951, pp. 31-32. (11) (a) NBS certificate for standard sample 39f; (b) R . S. Jessup, J. Resenrch h’nfl. Bur. Sfandards, 36, 421 (1946); (c) ibid., 29, 247 (1942). (12) Mean of six experiments, average deviation 0.007%, maximum spread 0.025%. (13) Mean of six experiments, average deviation 0.009%, maximum spread 0.034%.
111
'r.4BLE
S U M M A R Y O F FURAN C O M B V s l I O S S
Combustlsn.a
Llass of luraii.
N a s i of
Nabs u i
oi1.b
fuse.'
I10
6.
E
g.
sB.d SI? cal d e g -: cal dcg
0.82130 i').LI2992 0.00392 ,83189 ,04282 ,00389 ,83437 .01.538 .00408 88128 .01211 .i)05% %I7O!i . ! t ( @ + l oO,5X1
2B 4B 9-4 lciA
17.4
:i 33 :3.3L5 X3.1
3192.8 i3192.8 3192.8 3193.7 *'319.'j.7
mso8,8 alp",
.SF,d
cal. deg.-l
-1
3.52
-3.53
:j. 75'
:L52 3.93'
:I 76'
.'j
cal.
AI
1.99095 2.06058 2.01631 2.07253 2.11575
1.2
1.2 1.2 0.8
cal
1.28 1.28 1.28 1.28 2.66'
Deviation -ACB/.W.~
cal. g
-1
7314.3 7315.9 7315.1 7314.1
from mean, cal. g,-!
-0.7
4- .R
+-
,1 ,9
7315.5 $. .;i .ti Average 731\5.0 i 0 . 6 = 0.01c'; Maximum spread 1 . 8 cal. g . - ' = 0.025:; a In combustions 2 and 4 sample B was burned. Sample A was used in the other three combustions. In combustions 2 and 4 the heat of combustion of the oil was 11,265 cal. g.-'. In the other combustions, 11,272 cal. g.-I. The heat of combustion of the filter paper fuse was 3902.5 cal. g,--'. SB= energy equivalent of system minus contents; .SI= energy equivalent of initial contents; SF = energy equivalent of final contents; ACB/M = energy of bomb process per g. e Cor1/2 Ha0 514 0 2 HNOa(aq), ACT = -13.82 kcal. mole-' [E. J. Prosen and rection for nitric acid formed; 1/2 ?;2 F. D. Rossini, J . Research Xatl. Bur. Staizdards, 33, 264 (1941)l. f I n combustions 16 and 17 the platinum baffle was used (see text). 9 Duc t o mechanical failure of thc firing mechanism, twice the riorrnal ignition energy was delivered in combustion 17.
+
+
Ampoule Technique.--The furuti was enclosed iii sealed, soft-glass ampoules selected so that the quantities of furan contained were nearly sufficient to produce a 2" temperature rise in the combustion experiments. The mass of each sample was determined from the difference between the weights of the empty and filled ampoules. The technique used in this Laboratory for handling volatile materials has not been described previously and differs in several details from that employed by other workers. The ampoules used were about 80 mg. in weight, 12 mni. in diameter, and flattened on two sides. The stem of each ampoule was drawn down to a fine capillary, and :i glass tuhc was slipped m-er each capillary for protcctioii, :is shoivti in Fig. 1B.
TO VACUUM
TO HELIUM
-
recciver ((1). After the system was evacuated, the break-of7 tip was opened arid the furan was distilled into the calibrated receiver (b). Then a slight excess over the amount needed to fill the ampoules was distilled into the second rcceiver (d). The distillation was stopped, and dry helium \vas cautiously admitted to the system, causing the ampoules to fill. After the system reached room temperature and pressure, the ampoules were removed. The ampoules were held in a special pair of forceps and sealed, using a very sharp oxyhydrogen flame." The furan in the capillary stem a t the time of sealing protected the sample from moisture in the air. The ampoules and their capillaries then were placed iii a vacuum desiccator for removal of surface furan and for storage. Later, a t the beginuing of each conibustion experiment, an ampoule and its stern were weighed together. Experimental Results.-In nil, 17 combustion esperimerits were performed with furan. The results of only 3 were included in the final average. The remaining 12 experiments showed evidence of incomplete combustion or explosion and were discarded. In 2 of the 12 unsatisfactory combustions, the ampoule failed to fire, although the fuse burned. Six experiments were discarded because carbon was deposited on the bomb; in a t least five of these experiments the reactions occurred explosively. In each of four other combustions (numbers 8, 10, 13 :ind 1 5 ) there were rieithcr carbon deppsits nor cvidences of explosion. The values of - l l ' ~ ~ ~obtained l l i i i thesc experiments were 7239, iltici, 7247 and 7265 cal. 5. - I , respectively. These low and erratic results suggest incoinpletc reactions with products other than carbon dioxide a i d watcr. Unfortunately, carboii dioxide analyses of the bomb gascs could not be made a t the time of these experiments, Table I11 gives the results of the five accepted combustioil experiments and shows the correction terms. It is believed that these five combustions we@ complete, since it is highly improbable t h a t the precision of a group of incomplete combustions would be comparable to t h a t of benzoic acid. The presence of 0.01 mole % of isopentane would increasc the heat of combustion of pure furan by 0.1cal. g . - I . Yo correction has bcen made for impurity. T h c tiie:tii value of these five experiment5 has been u ~ c dt o culculate the follovkg derived therixtl data in keLt1. inok ' for furan ;it ?.io:
-.l(.i? W Fig. l.-A,
filling system; B, ampoule and supporting glass tube; C, sealed ampoule.
The all glass system used for filling the ampoules is illustrated schematically in Fig. 1A. -4 bulb with internal 1)reak-off tip ( ; I i cont:riniiig the furan \V:IS sealed to the sysi c m a n d the I--tulje !c j \\.a,filled with a drying agent (magiie.;iuni pcrch1or:~tci . E ~ r c h of several weighed arnpoulcs \\-it11it> >upportiiig t u l x \ v c ~ \i)laci.(i, c:ci,ill:iry i l o w i i , i i i the
497 07
-1Ifrt 49; ,97
- lriyil) -l,!ff(g)'" i4,90 s :I4
- llf:(gJ'''' li,2s
A I ' I ~\vu5 coinyutecl usiiig the Washburn correctioii,ltiA[',< = (1 I ) A U B , where I = -0.0056. The heat of combustion a t constant pressure, - A H R , is given for liquid furan and for
+
_____
(14) T h e technique for sealing ampoules has since been improved b y using a very small (I/* X mm.) flame obtained by burning HZ at the end of a very fine capillary. This technique was demonstrated !,y Lars 13jelleriip r , f t h e University clf 1,und. Sweclen. (1.7) {:II At s a t u r a t i o n presiure (600 mm.1, rhl at unit fujiacity (11:) I: \\. l V , ~ 4 , l > t \ r n.I R i $ c , i ,ill \ i i / i Iiir: ' I!J.i.l
Sept. 20, 1952
THERMODYNAMIC PROPERTIES OF FURAN
the real gases a t 1a t m . The heat of formation of liquid furan \vas calculated using the values -68.3174""and -94.051817b kcal. mole-' for the heats of formation of water and carbon dioxide from the elements in their respective standard itates.Ig The heats of formation of furan a t saturation pressure and a t unit fugacity were obtained using the heat of vaporization and gas imperfection data reported elsewhere in this paper. Discussion.--Landrieu, Baylocq and Johnson1) have reported 7352 t a l . g.-' for -AL.B,'JI for the combustion of liquid furan. The disagreement with the value found in the present research can be attributed principally to the absence of certsin corrections in the earlier work and to tliffcrence b e t w e n the purity of the t\vo samples. The resonance energy of furan has been calculated from the old value of the heat of combustion by Pauling, by \Vheland and by l?rctiiklin.2 Ysing the present value, the resonance energy cnlculated by the different methods of these authors will he raised about 1 kcsl. mole-' to 23.7, 24.6 arid 33.6 kcal. inole-:, respectively. I n '111 alternative calculation using heat of hydrogenation data, \Vheland?l has obt,iinetl 1, kc:il. mole-' for the resonance energy of furan. The differelice I,etn.ecn thii value aiid the value obtained from heat of combustion d a t d is far greater than the experi:]]ental uncertainties of the tivo thermocheniical mcasurc:iients. 'This dixrepancy probably arises from the different approximatioris used i n the two methods of estimating the cnergy of rioii-resonating furan. Low Temperature Thermal Data The Apparatus.-The meawrements \Yere made in an adiabatic calorimetric Yystem described by Kuehrwein and Huffman.22 .$bout J . , mole of furan was contained in a healed, copptr c,iloriinc.ter, which t v 2 > inounted in the calorimetric syitcm. Measured amouuts of electrical energy were supplied to the czilorirncter, and t h t initial and final ternperaturci \vert' Littcrmincd ivith a platinum resistance therrnomettr. During niea;ureinet~t~,the temperature of the environlnciit \ v a s Inaintaincd equal to that of the calorimeter to prevtnr he.it i:iterchLcnge. The precisioii of the measurements \ v a s . in general, better than U.170; and above 30°K. it is believed that the absolute uncertainty is not greater than (J.25.$. The Results. --Thermal measurements on furan beriveen 12 and 3 ~ 0 ' K .sho\v 3 small lambda point a t 56'K., a transition a t 1.jIJ'K. and fusion a t ld7.55'1;. The heat capacity, heat of ftision, melting point, heat of transition and transition temperature were determined. The experimental heat cdpacitv data are giver] i n Tctble I\.. The temperatures listed i t r r nieaii telilperhturcj oi the individual measureinelits. C'+,.i. is rht hecatcapacity of the condensed phase under its t ~ \ v i iv;,por 1Jrtsurt. The lainbd;, point b e t w e n 311 sild t>UCK.,\ \ - i t t i I niaxiinuni a t Libout one day) through the transition showed no further observable dependence on the thermal treatment of the sample, and i t is believed that the measurements below 150' reported in Table IV are characteristic of the equilibrium phase.
TABLE IV
MOLAL HEATCAPACITY O F FURAN. CAL. DEG.-1 T , OK.
AT
Csatd.
Crystals I 11.72 0.704 0,919 12.64 1.151 1.096 12.73 1.520 1.125 13.97 1.517 1.416 14.58 2.204 1.546 15.67 1.895 1.795 16.90 2.443 2.073 17.74 2.232 2.267 19.38 2.512 2.657 20.04 2.373 2.814 22.04 2.793 3.287 22.45 2.437 3.384 24.82 2.302 3.922 25.03 3.184 3.974 27.55 3.151 4.523 28.15 3.054 4.649 30.50 2.727 5.140 31.32 3.280 5.314 33.37 3.009 5,723 34.50 3.094 5.939 37.88 3.666 6.552 41.76 4.091 7.194 46.10 4.588 7 . 8 2 4 50.49 4.184 8.404 53.53 1.882 8.765 53.56 1.902 8.769 54.02 4.915 8.809 54.80 3.879 8 . 8 9 0 55.00 4.836 8.915 55.44 1.847 8.956 55.68 2.427 8.988 57.26 1.801 9.100 58.36 2.935 9.168 5 8 . 7 8 4.600 9.201 59.03 4.584 9.224 59.20 2.074 9 . 2 2 1 61.52 3.381 9.422 63.91 5.173 9 . 6 2 3 68.43 4.931 9.945 69.97 6.962 10.059 73.63 5.471 10.290 78.98 5.226 10.619 84.10 5.019 10.927 89.03 4.853 11.181 93.82 4.723 11.382 95.54 6.716 11.452 103.50 9 . 2 0 6 11.789 112.51 8.816 12.192 119.44 6,776 12.545
T , OK.
4T
Csatd.
121.16 125.55 126.11 129.48 129.72 132.22 132.58 136.72 142.18
8.474 12.604 6.774 12.851 6.570 12.857 8.165 13.033 6.670 13.038 6.563 13.224 6.374 13.219 6.317 13.468 4.612 13.849 Crystals 11 153.27 5.231 17.169 153.38 5.336 17.188 154.41 5.201 17.278 155.47 4.458 17.345 156.75 5.226 17.392 158.66 5.236 17.496 158.88 5.987 17.503 159.57 5.118 17.547 160.77 6.135 17.624 163.85 5,145 17.792 166.84 6.005 18,008 169.36 5.878 18.176 172.78 5.870 18.448 175.18 5.747 18.627 178.58 5.727 18.961 183.75 4.612 20.488 Liquid 191.00 3.498 23.857 194.14 5.299 23.899 196.23 6.955 23.921 200.31 7 . 0 2 5 23.990 203.16 6.9U5 24.033 207.74 7.844 24.122 210.04 6.854 24.161 217.29 7.650 24.309 225.32 8.416 24.520 233.64 8 . 3 2 5 24.755 241.97 8.230 25.030 250.15 8.135 25.312 256.25 9.530 25.540 258.24 8.032 25.637 265.71 9.396 25.917 266.22 7.911 25.933 274.11 7.840 26 284 275.42 10.022 26.319 282.29 8.517 26.630 0 864 26.778 285.36 290.75 8.398 27.038 294.77 8 . S(i5 27,229 299.09 8 . 2 8 5 27.440
i L) D \\ . a ; r n . t ~ i , J I: K l l p d t r l c k , \\' J 'U.iyi\sr, K 5 . Pirrer 1). I < < . - i n i , : L i ! , 3 4 , I 4 3 1,1.1-, , 1 ) I: J l'r#.
