Coefficient of Thermal Expansion of, and Sound Speed through,
Nitromet ha ne a nd Four Bis( difluora mino)aIkanes B. 0.REESE, 1. 8. SEELY, ROBERT SHAW, and DEREK TEGG Calif. 94025
Stanford Research Institute, Menlo Park,
Measurements have been made of the coefficients of thermal expansion of, and the sound speed through, the following liquids: nitromethane, 1,2-bis(difluoramino)propane, 2,2-bis(difluoramino)propane, 1,2-bis(difluoramino)butane, and 1,2-bis(difluoramino)-2-methylpropane. These results have been combined with previously measured or estimated heat capacities at constant pressure, C,, for these liquids to obtain values for the heat capacities at constant volume, C?;. C, for trinitrotoluene has been calculated from similar experimental values already reported.
THEH E A T CAPACITY a t constant volume, c,, is a n
important quantity in thermal explosion theory ( 1 , 4, 7 ) . It is difficult to measure C, and i t has been the practice to assume t h a t C, is equal to the heat capacity a t constant pressure C,. The two heat capacities a r e related thermodynamically ( 1 5 ) by
pane [ (CH,) ,CH ( N F , ) CH2NF2, IBA] , a measurement of the heat capacity a t constant pressure and 25" C. of 1,2-DP, and estimates of t h e C, of the other bis(difluoramino) alkanes. F r o m the above results and previously reported d a t a f o r nitromethane and trinitrotoluene, Equation 3 was used to calculate C, for t h e six liquid explosives, EXPERIMENTAL
T h e thermodynamic equation f o r U , the velocity of sound through a substance ( 1 2 ) , is
Eliminating
cu =
($)* from 1
Equations 1 and 2 gives
c, + [ ( M Ta2U2) (2.39 X 10--8)/Cn]
(3)
where M is the molecular weight, T is the temperature 1 av is t h e volumetric coefficient of in OK,, a o r -
(z) 1)
thermal expansion in deg.-l, U is the velocity of sound in cm. set.-', and 2.39 X converts t h e units from e r g s to calories. C, and C, a r e in units of cal. mole-' deg.-'. F o r solids ( 2 1 ) the difference between C, and C, is small. F o r example, in the case of copper a t 20" C., C, = 5.7 and C, = 5.9 cal. mole-' deg.-', a difference of about 3 % . However, for liquids the approximation is not so good. From tables (15) of heat capacities a t 25" C., for benzene C, = 23.0 and C, = 32.5 cal. mole-' deg.-', for n-heptane C, = 41.8 and C, = 53.0 cal. mole-' deg.-', f o r diethyl ether C, = 30.1 and C, = 41.0 cal. mole-' deg.-l, and f o r carbon tetrachloride C, = 21.8 and C, = 31.6 cal. mole-' deg.-'. I n each case, C, is about 70% of the corresponding C,. This article reports measurements at 25" C. of t h e coefficients of expansion and sound velocities of nitromethane ( CH,N02, N M ) ; 1,2-bis( difluoramino) propane, [CH,(NF,) C H ( N F , ) CH,, 1,2-DP] ; 2,2-bis(difluoramino) propane, [CH,3C(NF,) rCH,, 2,2-DP] ; 1,2b i s ( d i f l u o r a m i n o ) b u t a n e [ C H , ( N F , ) C H ( N F 2 ) CH2CH,, 1,2-DBl ; and 1,2-bis (difluoramino)-2-methylpro140
Journal of Chemical and Engineering Dota, Vol. 15, No. 1, 1970
Materials. Nitromethane was obtained from the Commercial Solvents Corp., S a n Jose, Calif. GLC analysis gave 96.5% nitromethane, 2 . 3 7 ~nitroethane, and 1.2% nitropropane. Karl Fischer analysis by E . Willis showed 0.1% water. A solution of 1,2-DP in methylene chloride was obtained f r o m Rohm and Haas. The methylene chloride was distilled off. The 1,2-DP was shown to be 99.0% pure by GLC. A solution of 2,2-DP in the high-boiling chlorinated solvent, Arochlor 1248, was obtained from the AerojetGeneral Corp. The 2,2-DP was distilled. No impurities could be detected by GLC, and i t was inferred t h a t t h e 2,2-DP was essentially 100% pure. A solution of 1,2-DB in methylene chloride was obtained from the Naval Propellant P l a n t a t Indian Head, Md. The methylene chloride was distilled and the residual 1,2-DB shown to be 99.0% pure by GLC. A solution of IBA in Arochlor 1248 was obtained from Rohm and Haas. The I B A was distilled and shown to be 99.2% pure by GLC. Heat Capacity at Constant Pressure. Eding has measured C, of 1,2-DP a t 25" C. to be 0.348 0.005 cal. gram-' deg:', which corresponds to 5 1 f 1 cal. mole-' deg.-'. This result has not been previously reported. The appar a t u s was a drop calorimeter ( 2 ) . The values of C, f o r the other bis (difluoramino) alkanes were estimated by comparison with their hydrocarbon analogs ( 1 7 ) to be 2,2-DP 51, 1,Z-DB 58, and IBA 58 cal. mole-' deg.-l. Coefficient of Expansion. Two 1-ml. (approximately) pycnometers were calibrated (IO) a t 20" C., using freshly distilled water. The calibration was checked using benzene (analytical reagent g r a d e ) , and a value of 0.8816 g r a m ml.-' a t 20" C. was obtained. This may (IO), be compared with values of 0.87893 g r a m ml:' 0.87890 g r a m ml,-l ( 1 8 ) , and 0.87985 g r a m ml.-l (20). The experimental e r r o r of the density measurements is probably of the order of 0.002 gram rnl.-'.
*
Table I. Density as a Function of Temperature from NM, 1,2-DP, 2,2-DP, 1,2-DB, and IBA
Compound NM
Density, 5OC.
15'C.
1.154 1.156
1.140 1.141
p,
Grams M1.-' 30" C.
20°C.
25°C.
1.1382
1.126 1.128 1.1313
Ref. 40" C.
35°C.
Grams M1.-1 Deg.-'
1.112 1.114 1.1244
Deg.-l
1.40 f 0.00 1.39 f 0.05 1.377 f 0.00
1.24 1.23 1.217 1.321
This work This work
1.59 f 0.07
1.26
This work
(19 ) (8)
1,2-DP
1.296
1.282
1.265
2,2-DP
1.288 1.286
1.270 1.269
1.254 1.253
1.236 1.236
1.72 f 0.06 1.66 f 0.03
1.37 1.32
1.202
1.44 f 0.03
1.18
This work This work (14 ) This work
1.39 f 0.05
1.15
This work
1.241
1.259 1,2-DB
1.245
1.231
1.216
IBA
1.242
1.227
1.213
1.193
T h e densities of nitromethane ( i n duplicate), 2,Z-DP ( i n duplicate), 1,2-DP, 1,2-DB, and I B A were measured at four temperatures between 5" and 40" C. (Table I ) . T h e slopes of the density-temperature plots were found by t h e method of least squares. The e r r o r s quoted in Table I a r e twice the standard deviations. Velocity of Sound. The velocity of sound in nitromethane, 1,2-DP, 2,2-DP, IBA, and 1,2-DB was measured at 25" C. using t h e following technique ( 6 , 1 6 ) . The liquid column varying in length f r o m 4 to 1 2 mm. was contained in a Tygon vinyl tube 12.5 mm. in diameter. T h e tube was filled and a i r bubbles were removed by hypodermic needles. A PZT-4 piezoelectric transducer produced a sinusoidal 1-MHz. sec.-l mechanical wave a t the bottom of t h e column. A similar transducer at t h e end of t h e column received the sound wave and reconverted it to electrical output. Oscilloscopic display showed directly the time f o r traverse of t h e liquid column. A precision time-sweep generator was used to allow measurement of t h e t r a v e r s e time to kO.01 psec. The upper transducer was held in a sliding fixture which had a micrometer attached so t h a t the column length could be measured to t 0 . 0 1 mm. The distance-time d a t a were fitted by least squares t o a straight-line velocity. A typical plot is in F i g u r e 1. I n t h e absence of liquid no signal was detected. T h e straight-line velocity did not go through the origin because of brass shims on t h e ends of the transducers and because of electronic delays. The results, in units of mm. psec.", were 1,2-DP 0.96 0.02, 2,2-DP 0.89 0.03, I B A 0.90 -+ 0.05, and 1,2-DB 1.00 -+ 0.07. For nitromethane, the results of duplicate
*
*
0
2
4 6 TIME. T - p w
8
10
I2
Figure 1. Measurement of velocity of sound in 1,2-DB
experiments r u n several weeks a p a r t were 1.29 2 0.05 and 1.31 0.05 mm. psec.-'. These values a r e in good agreement with 1.34 (3, 1 1 ) and 1.28 mm. psec.-l ( 5 ) .
*
RESULTS AND DISCUSSION
T h e heat capacity a t constant volume was calculated from Equation 3 f o r t h e six liquid explosives (Table 11). The values of C,. a r e between 61 and 83% of the corresponding values of C,.
Table II. Data for the Calculation of C,:
Compound NM TN Tc 1,2-DP 2,2-DP 1,Z-DB IBA
Mol. Weight
Temp.,
103 1,
OK.
Deg.-l
61 227 146 146 160 160
298 354 298 298 298 298
1.22 1.05 1.26 1.34
10-5
Ref. (3) d d
1.18
d
1.15
d
c,
C,.
CP,
Cm. Sec.-l
Ref.
1.30 1.61 0.96 0.89 1.00 0.90
h
(13) h h
h
Cal. Mole-' Deg.-' 25.4 87 51 51 58 58
9
Ref. (9)
( 31
Cal. Mole-' Deg.-l 17.8 53.3 39.3 39.5 45.5 47.9
Table I, (19). This work, see text. Trinitrotoluene, CH,C6H2 d Table I. Estimated, see text.
Journal of Chemical and Engineering Data, Vol. 15, No. 1, 1970
141
ACKNOWLEDGMENT We are indebted t o B. Y. Lew, J. H. Blackburn, Michael Cowperthwaite, M. E. Hill, and R. W. Woolfolk, Stanford Research Institute, f o r helpful discussion. LITERATURE CITED
Campbell, A. W., Davis, W. C., Travis, J. R., Phys. Fluids 4, 498 (1961). Cubicciotti, D., Eding, _. H., J. CHEM. ENG. DATA 10, 345 (1965). Enig, J. W., Petrone, F. J., P h y s . Fluids 9, 398 (1966). Evans. M. W.. J . C h e m . Phws. 36. 193 (1962). Gibson, F. C.,’ Watson, R. Hay, J: E., Summers, C. R., Ribovich, J., Scott, F. H., Quarterly Report, U. S. Dept. Interior, Bur. Mines, Pittsburgh, Pa., prepared for Bur. Naval Weapons, Order 19-65-8023WEPS, 1964. Goettelman, R. C., Evans, M. W., N a t u r e 198, 679 (1963). Hubbard, H. W., Johnson, M. H., J . A p p l . Phys. 30, 765 (1959). Kretschmar, G. G., J e t Propulsion 24, 379 (1954). Jones, W. M., Giauque, W. F., J . Am. Chem. SOC.69, 983 (1947). Lipkin, M. R., Davidson, J. A., Harvey, W. T., Kurtz, S. S., I n d . Eng. C h e m . 16, 55 (1944). Mader, C. L., personal communication t o Enig and Petrone, quoted in (3).
(12) Pitzer, K. S., Brewer, L., “Thermodynamics,” by G. N. Lewis and M. Randall, 2nd ed., p, 109, McGraw-Hill, New York, 1961. (13) Ramsay, J. B., Popolato, A., 4th Symposium on Detonation, ACR-126, sponsored by U. S. Naval Ordnance Laboratory in cooDeration with Office of Naval Research, Dept. of Ngvy, Washington, D. C., Oct. 12-15, 1965, p. 233. (14) Rohm and Haas, Report P-63-9, Contract Nos. DA-01021-ORD-11878 and 11879, “Process Research,” June 17, 1963. (15) Rowlinson, J. S., “Liquids and Liquid Mixtures,” pp. 14, 37, Academic Press, New York, 1959. (16) Schmidt, D. N., Linde, R. K., Stanford Research Institute, SRI Project PGU 6127, Contract A F 261601)7236, Tech. Rept. AFWL-TR-68-33 (July 1968). (17) Shaw, R., J. CHEM.ENG.DATA14,461 (1969). (18) Timmermans, J., Martin, F., J . Chem. Phys. 23, 747 (1926). (19) Toops, E. E., J . P h y s . Chem. 60, 304 (1956). (20) Wojciechowski, M., J . Res. Natl. Bur. S t d . 19, 347 (1937). (21) Worthing, A. G., Halliday, D., “Heat,” p. 135, Wiley, New York, 1948.
RECEIVED f o r review December 11, 1968. Accepted September 18, 1969. Work supported by the Office of Naval Research under Contract Nonr 3760 (00).
Solubility of Lithium Bromide in Water between
-500 and +lo00 C. (45 to 70% Lithium Bromide) DANIEL A. BORYTA Research & Engineering Laboratories, Foote Mineral Co., Exton, Pa.
19341
The solubility curve between 45 and 70 weight % lithium bromide was studied and compared with published results. Solubility measurements were i n good agreement with reported values obtained using the same technique. The addition of a small amount of lithium hydroxide or hydrogen bromide has a minimal effect on the solubility of lithium bromide.
T H E SOLUBILITY of lithium bromide i n w a t e r has been studied by many investigators as listed by Linke and Seidell ( 6 ) , who point out t h a t there is poor agreement among published values, especially in the range of interest to t h e air-conditioning field (2, 9 ) . T h e spread of these values is demonstrated in F i g u r e 1, which illust r a t e s why this system has remained a subject f o r continuing research. The present study attempts to define t h e solubility curve, correlate t h e results with literature values, and show the effects of a small excess of lithium hydroxide and hydrogen bromide on t h e solubility, in the temperat u r e range between -50” and f 1 0 0 ” C. which encompasses a concentration of 45 and 75 weight % lithium bromide. EXPERIMENTAL
P u r e L i B r w a s prepared i n solution f r o m certified
ACS HBr ( F i s h e r Scientific Go.) and spectrographically 142
Journal of Chemical and Engineering Data, Vol. 15, No. 1, 1970
pure Li,CO, (Foote Mineral Co.) . Recrystallized LiOH . H 2 0 o r H B r was added to adjust t h e p H to 7. T h e p H of t h e neutral brine was measured on a diluted sample (1 p a r t of brine to 10 p a r t s of distilled w a t e r ) , The desired concentration was finally obtained by evaporation o r addition of water to ensure t h e presence of both a solid and a liquid phase. The bromide ion concentration i n t h e saturated solution w a s determined by titration techniques using standardized silver n i t r a t e and potassium chromate as a n indicator. The solubility technique involved maintaining the solid and liquid phase together in a sealed polypropylene container submerged i n a constant temperature bath f o r a minimum of 3 hours, with stirring. Samples maintained a t constant temperature f o r a longer time (15 hours) did not give different values, indicating t h a t equilibrium w a s attained. A f t e r t h e 3-hour period, t h e temperature of t h e mixture was measured at 1-hour intervals using copper-constantan thermocouples and a Wheatstone bridge.
