INDUSTRIAL AND ENGINEERING CHEMISTRY
850
twenty-three perfumes tested in both laboratories except in the case of sweet-orange where the difference is 0.00004 and artificial wintergreen where the difference is 0.00005. No allowance was made for the coefficient of expansion of the glass in the pycnometers. This should make a difference of about 0.0005 in the specific gravity at the maximum temperature of 35”. I n determining the specific gravity with a plummet balance a t the same temperature, however, this error would be exactly compensated, assuming that the glass of the plummet and that of the pycnometer have the same coefficient of expansion.
VOL. 28, NO. 7
Literature Cited (1)
Gildermeister and Hoffmann, “Volatile Oils,” 3rd German ed.,
Vol. I, p. 702 (1913); 2nd English ed., Vol. I, p. 559 (1928). (2) Irk, K,, p h a r m . Zentraihalle, 55, 831 (1914). (3) Lyons, Proc. ~ i c hPharm. . A S S O C . , 1885, 203. (4) Sohimme1 & Co., Report, April, 1887, p. 45; Pharm. Arch., 4, 167 (1901). ( 5 ) Schimmel co., Report, Oct., 1905, p. 87, (6) I b i d , , ~ ~ ~1906, i lp. ,71. (7) Schreiner and Downer, Pharm. Arch., 4, 167 (1901). ~
R~CEIVE .4pril D 16, 1936.
Compressibility of BUTANE-AIR MIXTURES below One Atmosphere F. W. JESSEN AND J. H. LIGHTFOOT Humble Oil & Refining C o m p a n y , Houston, Texas
+
TO R E S E R V O I R
ro
The method employed in this investigation was essentially t h a t of Guye and Batuecas (6). Since the apparatus and method have been fully described elsewhere ( 5 ) , only a brief outline is presented here. Figure 1illustrates the apparatus.
VACUUM
The gas chamber consisted of three glass bulbs of approximately 220-cc. capacity each, connected with I-mm. capillary tubing. The volume of the gas chamber was varied by filling the lower and middle bulb, respectively, with mercury. The gas under consideration was admitted t o volume I until the pressure was approximately one-third atmosphere. The mercury in the manometer was brought to the reference point and the mercury column height read. The data were completed by reading the mercury column height with the gas subsequently occupying volume I1 and then volume 111. The volume of the separate bulbs and “nuisance” volume (the volume of the capillary tubing and small volume to the reference point) were obtained by calibration with triple-distilled mercury. The results (in cc.) are as follows:
’HERMOM iEATER
;TI R R E R
Bulb 1 Bulbs 1 and 2
I
FIGURE1. DIAGRAM OF APPARATUS
@T
HE use of readily liquefiable gases for fuel, light, and domestic purposes has led to a n ever-increasing demand for commercia1 butane and propane. Recently a number of municipal gas systems which use a mixture of butane and air have been installed. A knowledge of the compressibility of such a gas mixture is of importance in the design and operation of plants that use this type of fuel supply. The purpose of this investigation was to determine the pressure-volumetemperature relations of gaseous mixtures of air and butane a t pressures below one atmosphere. The literature records no compressibility measurements for butane-air mixtures. For air (1 A) = 1.00061 at 0” C. and one atmosphere (6). Lebeau ( 7 ) and Oudinoff (8) report a value of (1 A) = 1.0437 for n-butane at 0 ” C. and one atmosphere. Beckers (2) found that for n-butane ( p u ) = ~ ~0.997013; ~ Felsing and Jessen (4) obtained a value of (1 A) = 1.04212 a t 0’ C. and one atmosphere. Batuecas ( 1 ) has calculated (1 A) = 1.0419 from the data of Seibert and Burrell (9).
+
+
+
+
220.1372 438.8484
Bulbs 1, 2, and 3 “Nuisance” volume
665.8070 1.9694
The temperature of the water bath surrounding the gas chamber was maintained at 30” C. =t0.01’ by means of supersensitive thermoregulator and relay. A temperature correction of the “nuisance” volume was made for any variation in room temperature compared to that of the bath. All pressure measurements were observed by means of an absolute manometer, the mercury column heights being read to 0.03 mm. with a sensitive cathetometer. Proper correction for the meniscus was made. A 3-liter, round-bottom flask served as a mixing chamber and reservoir for the gases under consideration. The flask was first evacuated and then filled with one gaseous component until the partial pressure was that required for a definite mole per cent mixture. The other gaseous component was then allowed to fill the flask until the pressure reached atmospheric. To test the method of obtaining mixtures of definite mole percentages,
The compressibility of n-butane-air mixtures and of n-butane was determined at 30” C. I t is shown that the additive rule for determining the compressibility of gas mixtures at low pressure does not hold for butane and air, the maximum deviation being 23 per cent. Thevariation of the compressibility coefficient of nbutane with temperature is presented.
ISDUSTRIAL AND ENGINEERING CHEMISTRY
JULY, 1936
871
FIG 3-PV ISOTHERMAL5 AT 30" CENTIGRADE
FIG.~~COMPRESSIBILITY
018
FIG 4- VARIATION OF COEFFICIENT OF N-BUTPNE WITH TEMPERATURE
/i
d
* 03 034
,,/ CALCULATED
1
25 50 75 MOL. PER CENT BUTANE
0
AIR 400 MMHG
.OS SO0
600
700
800
,0038 ,0036 0034 ,0932 ,0030 .0028 0026
100
i
equal known volumes of but,ane and air at atmos heric pressure were mixed and allowed to reach equilibrium. g o measurable change in volume occurred. Density determinations showed that the composition of the mixturd was identical with that resulting when the composition was obtained by using partial pressures. Before making any compressibility det,ermination, the a paratus was evacuated for several hours. Gas was admittes t o the system from t,he reservoir (3-liter fla,.sk), and the system thoroughly flushed several times. It was then filled wit.h t'he gas for subsequent measurements. %-Butane of 99.5 per cent purity was obtained from the Ohio Chemical and Manufacturing Company. Carbon-dioxide-free and moisturefree air was used in all experiments.
Results The results of this investigation are presented in Table I. Values for (1 X) were calculated, using the expression
+
(1 + A) =
00
(1)
b)760
where ( P V ) ~ = pressure X volume at 0 pressure ( p o ) . ~= ~ pressure X volume at 760-nim. mercury
+
The separate (1 X) values listed are average values of three determinations. The maximum deviation between any two isolated values is 13 X 10-4; the largest variation Any error occurring in obtaining from the mean is 7 X definite compositions of the gas mixture is well v,+thin the h i t of experimental error, a one per cent error in composition resulting in a difference of *0.0005 in the compressibility value. Figure 2 shows the deviation of the compressibility from the additive rute. I n Figure 3 are plotted the pu isothermak a t 30" C. It has been shown (3, 6) that a t pressures not exceeding one atmosphere the compressibility coefficient thus obtained varies only slightly from that which results when the p 2 term is used in calculating pv and is generally within the limit of experimental error, This point is substantiated by the results of this investigation, although some curvature of the isothermals is indicated. From theoretical considerations Cawood and Patterson (8) hare derived the following relation between the compressibility coefficient A. and temperature:
The product of pressure X volume was obtained by means of the expression pv = a bp 4 cpz
+
where a, b, and c are constants which xere found from the experimental data. The pressure ( p ) and volume (v) are expressed in mm. of mercury and cc., respectively. TABLE I, V A L G EOF ~ (1 t X) FOR BETAXE-AIR MIXTCRES AT 8-_ n O c _. Mole % Butane 0
PI
....
pi
.. . . . .
Pz
.. . .
P,
12
.. ..
.
.,. ,
l;a
.. .. .
.
c, n =
constants
In order to determine the compressibility of n-butane at 30" C. from that a t 0" C., A, is plotted against 1/T as in Figure 4; the resulting value of A0 is 0.03642. Smce (1 X) is related (3)to AOby the equation
+
(1 $. X) =
+
1 X 1.000554
(1
+ A)
1 (1 - Ao)
= 1.03779
(3)
+
The experimentally determined value for (1 A) = 1.03278. The discrepancy between the calculated and obsened value of (1 X) a t 30" C. is beyond the limit of experimental error and may be due to the variation of the "constants" Q and b of the van der Waal equation from vhich the equation relating the conipressibility coefficient and the temperature was deduced.
+
I
50
252.99 253.04 253.16 230.20 230.39
657.7965 657.7965 657.7961 657.7888 657.7888
376.64 440.8379 376.69 440.8379 376.87 440.8375 342.79 440,8302 343.01 440.8302
743.76 222.1249 743.89 222.1256 744.36 222.1263 677.02 222.1191 677.43 222.1191 Average
1.01311 1,01338 1.01328 1,01290 1.01340 1.01391
75
236.76 236.69 243.13 243.18 260.94
657.7879 657.7897 657.7879 657.7940 667.7961
352.05 440.8293 351.98 440.8311 361.53 440.8311 361.48 440.8361 387.83 440.8435
692.68 692.55 211.24 ,11.13 762.74
222.1181 222.1199 222.1181 222.1249 222.1343 Average
1.02186 1.02146 1.02144 1.02293 1.02261 1.02206
100
246.94 241.30 258.93 248.86 258.98
657.7928 657.7961 657.8039 657,7940 651.7961
366.51 358.29 384.22 366.43 304.39
717.14 222.1249 701.19 222.1263 751.62 322.1304 716.93 222.1444 751.83 222.1263 Average
1.03345 1.03213 1.03332 1.03281 1.03216 1.03278
Calculated from Equation 3,
-
440.8361 410.8375 440,8416 440.8556 440.8416
Literature Cited (1) Batuecas, J . ckzm. phjis., 31, 165-83 (1931). (2) Beckers. Bull. soc. chim. Belg., 39, 470-95 (1930). (3) Cawood and Patterson, J. Chem. Soc., 1933, 619-24. (4) Felsing and Jessen, unpublished data, 1932. (5) Guve and Batuecas, J . china. phvs., 20, 308-36 (1923). (6) International Critical Tables, Vol. 111,p. 3, New York, McGrawHill Book Co., 1928. (7) Lebeau, Compt. r e n d , 140, 1454 (1905). (8) Oudinoff, Bull. soc. chim. Belg., 23, 266 (1909). (9) Seibert and Burrell, J. Am. Chem. Soc., 37, 2683 (1915). RECEIYBD Maroh 27, 1936.
