Nov., 1963
THERMODYNAMIC PROPERTIES
gelatin and ids coagulating action is different on silver bromide and silver iodide sols. The amount of gelatin irreversibly a,dsorbed onto silver bromide is less than 10/04646 and is less than our analytical techniques could measure. Increasing the temperature of the system has multiple effects. Fjrst, it reduces the viscosity of the system, and this, a5 explained earlier, should reduce the agglomeration by facilitating the movemeiit of the initially formed positive particles to the bulk solution where they become stabilized. Second, the adsorption of gelatin should be reduced a t higher temperatures, and this should reduce agglomeration. Third, the solubility of silver salts of gelatin are increased, which should again reduce the adsorption and therefore the agglomeration. Fourth, the solubility of the silver halides is increased and so the silver ion concentration does not have to be reduced to the same extent to stabilize the particles with the bromide ions. Fifth, relative to the bromide ions, the silver ions are more readily adsorbed than at lower temperatures, as evidenced by the shift of the isoionic pAg from the silver excess region towards the equivalence point. 26 Added polyvalent anions-the heteropoly acids and salts-did not reduce agglomeration. However, Mathai and O t t e ~ i 1 have 1 ~ ~ shown that in the presence of nonionic surfactants the effect of coagulating electrolytes is greatly reduced, and above a minimum concentration (the critical micelle concentration for surfactants) is nil. I t would appear that the adsorbed gelatin reduces the effect of added electrolyte. However, in the absence of gelatin, where coagulation was much greater, and in the presence and absence of gelatin using solutions diluted 100-fold, the heteropoly salts still did not reduce agglomeration noticeably. We suggest that in the presence of gelatin, the gelatin reduces the effect of added electrolyte, while in the absence of gelatin the over-all system is unstable be-
OF
3-AZABICYCLO NOSANE NO SANE
2373
cause the over-all electrolyte concentration makes the particles coagulate. Added surfactants, a8 shown in Table IV, did not reduce agglomeration materially, and in one case increased it. The cationic surfactant did reduce the volume of agglomerates, but the agglomerates settle rapidly and probably had a much higher packed density. One would expect a cationic surfactant to tend to flocculate particles protected by an anionic gelatin. The anionic surfactant had little effect, for it would not act much differently than the anionic gelatin. The nonionic material greatly increased the volume of agglomerate. We suspect that it could have been preferentially adsorbed and yet, because of its lack of charge, it may not have protected the particles sufficiently. Coiiclusions To summarize, we have confirmed earlier work that agglomeration of silver halide emulsions may be reduced by: (a) diluting the silver nitrate; (b) working at a pH above neutrality as by using ammonia; (c) working a t higher temperatures; (d) increasing the gelatin content (up to a certain point) ; and (e) reducing the iodide content in bromoiodide systems. We have also found that: (a) the isoelectric point and viscosity of the gelatin have little effect on agglonieration during the precipitation stage; (b) increased agitation reduces agglomeration; (c) the iodide content of the agglomerate in a broimoiodide system was less than the average value; and (id) the agglomeration tendency of gelatins increases with increasing reactivity toward silver nitrate. Acknowledgment.-The exploratory work of Jerome Reid is gratefully acknowledged. Much of the experimental program was cairried out by Richard Varney and George Whitehouse. Analyses were done by Peter Kliem. The heteropoly salts were kindly supplied by Prof. Matijevic of Clarkson College.
HEAT CAPA.CITIES AND THERMODYNAMIC PROPERTIES OF GLOBULAR MOLECULES. V. 3-AZABICYCLO [3,2,2]NO;"\'ANEFROM 5 TO 350°K. BY
CAROLYX
31. B.4RBER
ASD
EDGAR F. T~ESTRUM, J R . ~
Deparlmenl of Chemistry, Unzuersity of Michigan, Ann Arbor, Michigan Received M a y 14, 2963 The heat capacity of the globular molecule 3-azabicyclo[3,2,2]nonanewas determined by adiabatic calorimetry from 5 to 350°K. A transition to the plastically crystalline ("rotator") state was found a t 297.78'K. with an associated transitional entropy increment of 11.63 cal./mole-OK. At 298.15"K.the entropy ( S O ) , the enthalpy function [(HC - H'o)/T], and the Gibbs free energy function [ ( G O - H " o ) / T ]are 56.14, 33.39, and -22.75 cal./mole-'N:., respectively.
Introduction In conjunction with a series of studies on the thermodynamics of the transitions involved in the formation and fusion of the "p1,astically crystalline" or "rotator" phaseJ2+ the family of molecules of which bicyclo[2,2,2]octane is the prototype has proven interesting for study. Previoudy, triethylenediamine (1,4-diaza(1) To whom correspondence concerning this work should be addressed. S.8. Chang and E. F. 'Weatrum, Jr., J. Phgs. Chem., 64, 1547 (1960). (3) S. S. Chang and E. F. Westrum, Jr., i b i d . , 64, 1651 (1960). (4) S. S. Chang a.nd E. F. 'Westrum, Jr., ihid., 66, 834 (1962). ( 5 ) Jl. H. I'ltyne and E. F'. Weahrum, Jr., ( b i d . , 66, 748 (1962).
bicyclo [2,2,2]octane) has been studied over the low3 and intermediate6 temperature ranges, and low temperature data on iiorbornylane have received preliminary mention by Guthrie and McC~llough.~Another member of the family, 3-azabicyclo [3,2,2]iionane (CBHISN, hereafter AZBK) , offers further interesting possibilities for investigation of the nature of the plastically crystalline phase, for the t'ransitioii producing this phase occurs
(2)
( 6 ) . I . ( 2 . 'Tronhndee and E. F. \Vestrum, Jr., i b i d . , 67, 2381 (1963). ( 7 ) C;. 13. (:utllrie c t i i d ,I. 1'. h I ~ C u l l o u p 1 .I. ~ , P h p . Chsm. Solids, 16, 53 (I!Jtil),
CAROLYN M. BARBER AXD EDGAR F. WEST RUM^ JR.
2374
7; 'K.
100 I
0 I
8o
tt
200 1
I
Crystal
300
'
i l l
i
18
I
0
IO
20
30
7; 'K
Fig. 1.-Heat
capacity of 3-axabicyclo[3,2,2]nonane.
a t almost exactly 25'. AZBN is assumed to be a relatively new composition of matter since no references describing its preparation or properties have been found in the chemical literature. It has, however, recently been made commercially available by Eastman Chemical Products, Inc., and is stmatedto melt a t approximately 180°.8 Experimental Preparation and Characterization of Sample.--A reputedly 987, pure sample of the AZBN obtained from the Eastman Chemical Products, Inc. (Kingsport, Tennessee), was subsequently purified by several consecutive sublimations under high vacuum in a simple sublimation apparatus contained within the nitrogen atmosphere of a drybox. The resultant transparent crystals, apparently stable in dry air, become translucent in ambient air, possibly as a conEequence of the reported tendency of these hygroscopic crystals to adsorb water and carbon dioxide rapidly. For this reason handling of the sublimed crystals was minimized and the calorimeter was loaded with AZBN (43.087 g. i n vacuo) in the drybox to prevent contamination of the sample. Duplicate microchemical analysis indicate the composition t o be 12.14 i 0.077, hydrogen, 76.71 =t 0.08% carbon, 11.15 i 0.037, nitrogen (theoretical: 12.077, H , 76.747, C, and 11.19%
N). Cryostat and Calorimeter.-The Mark I1 adiabatic cryostat, a gold-plated copper calorimeter (laboratory designation W-28) and a calibrated platinum resistance thermometer (laboratory designation A-5) were used in measuring the heat capacity of this sample. The cryostatg and the adiabatic technique employed'O have been previously described. Helium gas a t 9.6 em. pressure at 300°K. provided thermal contact between the calorimeter and sample. A sample density of 1.14 g./cm.a was assumed for the buoyancy correction. The heat capacity of the calorimeterheater-thermometer assembly was determined in a separate series of measurements with small adjustments applied as needed for slight differences in the quantities of helium, thermal conductivity grease, and solder between the runs with and without sample. The heat capacity of the sample decreased from 90% of the total observed a t 15°K. to a minimum of 55y0 a t 110°K.; above this temperature (except in the transition) it steadily increases t o about 75% a t 350'K. Manual shield control %-as used below 100°K. Above this temperature, three separate channels of recording electronic circuitry provided with proportional, rate, and reset control (8) Technical D a t a Report No. X-119, Eastman Chemical Products, Inc., Kingsport, Tennessee, May, 1962. (9) E. F. Westrum. Jr., J . Chenz. Educ., 39, 443 (1962). (10) E. F. Westrum, Jr., J. B. Hatcher, and D. W. Osborne, J . Chem. Phys., 21, 419 (1953).
troi. 67
actions gave control of the temperature of the adiabatic shield to within approximately a millidegree, thereby reducing the energy exchanged between the calorimeter and surroundings t o a n amount negligible in comparison with other sources of error. All measurements of temperature, time, potential, resistance, and mass refer to calibrations or standards of the National Bureau of Standards.
Results and Discussion Heat Capacity.-The experimental data on the heat capacity of AZBN are presented in Table I in chronological order of the determinations so that the approximate temperature increments used usually may be estimated from the adjacent mean temperatures. A small adjustment for curvature has been applied to correct for the finite temperature increments used in the measurements. Precision reflected by probable errors decreasing from 5% a t 5', to 1% a t 12', to 0.1% a t 20'K., and to less than 0.1% a t higher temperatures is considered to characterize these data. The heat capacity data are depicted graphically in Fig. 1. These data are based on the molecular weight of 125.216 g., the defined thermochemical calorie of 4.184 abs. j., and an ice point of 273.15'K. The values of heat capacity at selected temperatures derived from a computer leastsquares fitted smooth curve through the experimental data points are presented in Table 11. These values accord well with those from a large-scale plot of the data. The Thermodynamic Functions.-The thermodynamic functions (also presented in Table 11) were obtained by exact integration of ai1 analytical expression through the experimental points by means of an IBM digital computer program.ll These functions are considered to have a probable error of less than 0.1% above 100'K. An additional digit beyond those significant often is included in order to provide internal consistency and to permit interpolation within the table. The heat capacity was extrapolated below 5'K. by means of the Debye T 3limiting relationship. Solid-Solid Transition-A very sharp, presumably first-order transition was discovered at 297.78"K. with apparent heat capacities as high as 5600 cal./mole-OK. The very slow rate of attainment of equilibrium occasioned corrections for drifts extending over periods as long as 12 to 14 hr. and rendered the small transitional temperature increments uncertain. Since it was not possible to determine heat capacity in the transition region with high accuracy, a number of enthalpy-type runs of various magnitudes were taken over the transition region to provide direct experimental values of enthalpy increments rather than heat capacity values. The results of these determinations are summarized in Table 111. It was noted from cooling curves made in the cryostat that an undercooling of about 7" was typical for this transition. To evaluate the transitional enthalpy and entropy, it is necessary to obtain an estimate of the "normal" lattice-vibrational heat capacity for this substance over the transition region. In this illstance it appears appropriate to extrapolate the heat capacity of the crystal I1 phase to the transition temperature and like(11) E. H. Justice, "Calculation of Heat Capacities and Derived Thermodynamic Functions from Thermal D a t a u i t h a Digltal Computer," Appendix t o Ph.D. dissertation, Cniversitq of Michigan; U. S. Atomic Eneigy Commission Report TID-12722, 1961.
Nov., 1963
TABLEI HEATCAPACITY OF 3-AZABICYCLO [3,2,2]NOXANE [Units: cal., mole, OK.] Ta
CPb
Series I 253.28 36.04 262.09 37.78 270.92 39.38 279.77 41.41 Trans. runs A Series I1 Trans. runs B 317.30 56.83 326.47 56.55 335.82 56.48 345.37 56.57 Series I11 5.20 5.73 6.18 6.67 7.33 8.14 9.02 9.95 10.99 12.20 13.31 TQ
0.036 .052 .070 .091 .140 .215 .330 ,478 ,645 .868 1.143
T
CP
14.68 16.23 17.68 19.10 20.75 22.84 25.25 27.69 30.29 33.60 37.64 41.99 46.35 50.82 55.39 60.20 65.36 70.59 76.07 82.06
1.505 1.950 2.396 2.845 3.378 4.059 4.818 5.559 6.281 7.143 8.066 8.909 9.648 10.329 10.950 11.594 12.232 12.803 13.415 14.122
Series IV 76.40 83.92 91.21 99.47 108.00 116.72
A TC
Transition runs A
CP
13.442 14.343 15.14 15.96 16.90 17.87 T
T
CP
125.57 18.79 134.23 19.78 20.73 142.88 21.75 151.79 160.88 22.81 169.64 23.85 178.33 24.91 25.98 187.03 195.85 27.15 204.88 28.39 213.92 29.68 31.05 223.09 32.51 232.29 34.03 241.28 35.25 248.66 36.51 225.94 38.99 269.16 Trans. runs C Series V 266.28 38.43 274.94 40.32 AHt run D Series V I
AHt run E AT
297.50 0.099 297.59 .074 297.67 ,081 297.73 .049 297.78 .045 297.82 .051 297.91 .116 298.09 ,242 299.44 2.465 302.33 3.316 308.36 8.758 Transition runs 281.88 7.730 286.79 2.048 288.93 2.240 291.03 1.046 301.05 18.0!)5
CP
2584 3444 3320 5219 5640 5002 2254 1032 84.69 57.64 57.21
287.96 7.934 45.05 294.29 4.967 101.0 296.87 0.899 644 297.40 .476 1231 297.63 .313 1885 297.85 ,430 1364 298.52 1.332 628 303.85 10.667 61.66 Transition runs B 291.45 2.740 58.81 C 293.88 2.155 99.61 41.83 295.39 0.946 161.0 43.20 2!)6.3 0 .507 317 47.04 2!16.70 ,762 651 56.86 297.17 ,185 1362 243.0 297.36 .I00 1331 a 2' is the incan temperature of the individual heat rapacity determinations. * Cp is the heat capacity of the crystal a t the essentially constant pressure (
