VAPOR PRESSURES O F SOME HYDROCARBONS BY ERNEST G . LINDER*
In making a series of vapor pressure measurements for use in an investigation of some electrical properties of hydrocarbons, serious disagreements were found with published data in standard tables, such as the International Critical Tables and the Landolt-Bornstein Tables. The purpose of this note is to give the new data obtained and to indicate the disagreements and likely reason therefor. Data also have been included on some hydrocarbons
,
M
~
L
E
~
O
\
I
A
B
FIG.I Vapor Pressure Apparatus
on which no previous determinations of vapor pressure seem to have been made. The measurements extend over only a rather small temperature range, because it was desired merely to obtain sufficient data to determine the vapor pressure at o°C. The method used for these measurements was a slight modification of that due to Ramsay and Young.' The apparatus is shown in Fig. I . The essential part is the glass chamber A, containing a thermometer T, with the bulb wrapped with two or three layers of cheesecloth saturated with the hydrocarbon whose vapor pressure is to be measured. B is a trap, cooled either by * Research associate, Cornel1 University. This work is a part of an investigation of organic reactions in electrical discharge, being carried on with a fund maintained by the Detroit Edison Co. J. Chem. SOC.,47, 45 (1885).
ERNEST G. LINDER
53 2
TABLE I Vapor Pressure of Hydrocarbons mm
t"C
V.P. Hg.
toluene - 9.7 3.53 - 8.7 3,77 - 7 .2 4.17 - 4'4 4.98
-
4.35
j
.oo
- 3.7 5.30 - 3.5 5.36 - 2.75 5.57 tetrahydronaphthalene - 2.4 ,015 ,0235 - I .2 .o
.40
65 . o
.83
25
m-xylene
-
8.4
6.75 - 2.8
.90 I .03 I .37
5.0
.IO
.5 3.3 11.75 14.25
'25 .3I
.55 .75
o-xylene
- 17 . o .6
1.10
p -x y 1ene - 9'5 - 2.5 .2
1.7 2.3 3.2
.34 50 .53
.33 .87 1.16
ethylbenzene -11.6 .S6 - I .2 I .38
t"C
n-octane - 9.3 .I .47 - 3.0 2 .32 3.7
3.65
durene
-
1.7 - 1.3 1. 3 S .f5
.o13 .or6 ,033 .033?'
19
.21
.*3 .47
5 5
. 2 j
.48
6 . 2
-
2.6
.32 .53
.82
1.051 I
.08
.49
.54 .83 1.35
m-diethylbenzene .8 6.8 10.8 15.7
"5 .30 .43 .74
n-propylbenzene
-
6.8 '7 3.6 13.9
.35 '58 .8j 1.95
iso-propylbenzene -
8.2
1.3 3 .7
sec-but ylbenzene - 8.6 .IO - 3.0 .18 9.8
.43
6.7 j.6 - 0.7
n-butylbenzene - 4'7 .IO 12.2
.27
2.3 10.8 13 . o 13.7
p-diethylbenzene
n-decane - 3.8 ,165 .5 8.5
2.0
-
.OOj - 2
.2
mm
V.P. Hg.
tert-butylbenzene
-
'
.20
.42
-10.7
mesitylene (E)
-
n-tetradecane
dipentene
-
mm V.P. Hg.
t"C
octylene - 9.0 - 2 .o 9.5
-
.43 .93 2.25
I . j j 2 . 7 0
6.02
di-iso-but ylene 9.5 8.3
5.12
5.75
VAPOR PRESSURES
OF SOXE HYDROCARBONS
533
TABLE I (Continued) Vapor Pressure of Hydrocarbons mm V.P. Hg.
t"C
2-2-4-trimethylpentane -30.5 - 19 . o
I
2
,ox .58
decane (di-iso-amyl) - 2.25 .43 '5 5 '5 10.3
'52 '"
1.10
hexameth ylet hane -10.3
1.33
-
2.08?'
5.0
.3
6 .O
3.55 j .80?
mm V.P. Hg.
t"C
phenylcyclohexane 12.4 ,017
2
.o
11.8
6.5 1.j
3.15 5.25
-
.23
.8 13.3
.25
.68
19.5
.02--?
mesitylene (Kb) .29 - 2.75
-
I .20
1.5
10.6
.33 .43 .9I
-
mesitylene (E) .28
4.2
.IO
2.7
.SO
2.5
.23
10.2
.9I
12.2
.54
acenaphthene
pinene
-
.o
diphenylmethane
- 5.3
1.17
.I 4 .I4
.80
'
- 9.6
'54
5'5 5.3
-38
3 I9 6 . SO?
--ri.o
.03 I
cyclohexene .65 I . I3 2.16
methylcyclohexene I .30 -26.2
.32?
p-cymene
14.6
I -met h ylcyclohexene
-
mm V.P. Hg.
methylnaphthalene
styrene - 7.7 - .5 8.2
limonene p-menthane - 4.9
t"C
6.00 I .oo 13.25
.4I .j2 I
.i8
20.0
.02-
o-diphenylbenzene 20
.o
.02-
dekahydronaphthalene - 4.2 ,IO - 0.2 '11
9.5 ,372 A question mark indicates doubt regarding presence of equilibrium when reading mas taken. 2 A minus sign after a figure indicates that the vapor pressure is less than the given figure. 1
liquid air or a carbon dioxide-ether slush. Connections are made as shown t o a McLeod gauge and vacuum pump. The three-liter flask C increases the
volume of the apparatus so that the McLeod gauge can function properly. I n operating the apparatus, the entire system was first pumped down until the thermometer, cooled by the evaporating hydrocarbon, registered a temperature near 0°C. The stopcock to the pump was then closed. After that, sufficient time was allowed for equilibrium to be reached, as indicated by a constant reading of the thermometer. Under equilibrium conditions the
534
ERSEST G. LINDER
part of the system to the left of trap B will be filled with hydrocarbon vapor, whereas nothing but air will be in the portion of the apparatus to the right of B. The air and vapor will be at the same pressure, hence the McLeod gauge will indicate the vapor pressure of the hydrocarbon at the temperature registered by the thermometer.
TABLE I1 Vapor Pressures at OC Suhstance
from published Tables
water toluene
\Toringer
4 55' 6 9i1
4.50
6.90
{ ;1:
naphthalene
Linder
.01;5
0 22
octylene n-decane p-menthane dipentene di-iso-amyl
4
o-xylene p-xylene mesitylene ethylbenzene n-propylbenzene n-octane iso-propylbenzene Landolt-Bornstein Tables. 2Wilson: Ind. Eng. Chem., 20,
002
3 . 2 0
3s2
.20
40'
.43
302 7 o2
'25 '
4.0
8.29 15.6
32j2
5.9 6.25 4 .oo 6.45
I
50
.06 .95
,375 1.57 .60
2.95 .82
l
I?,
1363 (1928).
This method is especially suited to the measurement of small vapor pressures, where considerable error is frequently committed due to gases absorbed in the liquid. This source of error is entirely absent in the method described here, since any gas given off by the hydrocarbon will be immediately swept over into the chamber C, and become merely a part of the gas contained there-in. Another advantage is that the vapor pressures of solids can be determined. To do this, it is only necessary to remove the cheesecloth wrapping from the thermometer bulb, and coat the bulb by dipping it in the molten hydrocarbon. The complete data are given in Table I. For some substances, e.g., n-tetradecane, the pump was incapable of reducing the pressure in the system down to the vapor pressure of the substance, hence, for these substances, it can be stated only that the vapor pressure is less than the given figure. Satisfactory checks of the accuracy of the method were made with water and toluene. These and some other comparisons are given in Table 11. Wilson's data were taken from a nomographic chart, and the agreement with
V.4POR PRESSURES O F SOME HYDROt2ARBONS
53 5
the writer’s data is very likely within the limits of accuracy of the chart in the region involved] especially since extrapolation on the chart was necessary in some cases. The writer’s data in the last column in the lower part of the table are in serious disagreement with Woringer’s data quoted in the other column.’ Woringer used a static method, Le., one in which the vapor is contained within a closed space and the pressure measured directly for different fixed temperatures. With such a method small traces of absorbed gases will cause serious errors at low pressures. I t seems likely that such an error was present. in Woringer’s measurements] especially since all his pressures, where there is a disagreement] are greater than the writer’s. I n the case of mesitylene (which shows the greatest disagreement) three runs were made by t,he writer. The first two were made on mesitylene from the Eastman Kodak Company, one being made with carbon dioxide-ether cooling and the other with liquid-air cooling on the trap. Both these runs gave 0 . 3 9 mm. of mercury for the vapor pressure at oo C. The third run was on Kahlbaum mesitylene. This gave 0.36 mm. of mercury. I t seems that these figures must be fairly correct.
Summnrv For thirty-nine hydrocarbons vapor pressure data in the neighborhood of 0°C. are presented. Some disagreements with published data in standard tables are pointed out and discussed. The writer wishes to express his appreciation to the Detroit Edison Company for the financial support which has made this investigation possible, and for the permission t o publish the data. Thanks are also due to the Physics Department of Cornel1 University for the laboratory facilities used. Cornell Unwerstty, Ithaea, ‘V. Y . J u l y , 1980. Z. physik. Chem., 34, 2j7
(1900).
