INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1930
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Vapor Pressure of Toluene up to the Critical Temperature' Norman W. Krase and J. B. Goodman CHEMISTRY DEPARTMENT, UNIVERSITY OF ILLINOIS, URBANA, ILL.
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HE development of industrial processes involving high temperatures and high pressures is becoming so rapid that knowledge of the properties of substances under these conditions is quite essential. As part of the program of fundamental research in this field started by this laboratory, apparatus and methods for the measurement of vapor pressures were developed. This paper describes the work and includes new data on toluene from the normal boiling point up to the critical temperature.
F
1
U
Power
Figure I-Apparatus
fii-cuif
c
for Determining Vapor Pressures a t High Temperatures
insulation. External resistance in the heating circuit manually regulated, permitted adjustment of the temperature. A chromel-alumel thermoelement placed in a small hole drilled in the steel wall of the bomb was read by means of a Leeds and Northrup type K potentiometer and galvanometer. Before connecting the bomb to the pressure measuring apparatus, the valve F was opened and a small amount of toluene boiled out to expel air. The valve was then closed and connected as shorn. C was a steel U-tube about half full of mercury. Above the left column was liquid toluene and above the right column a hydrocarbon oil which also filled all the tubing leading to the gage and to the mercury column. The U-tube C was shielded from room-temperature changes by asbestos paper insulation. By opening valve H the pressure was read by means of the p i s t o n g a g e , D. By closing this valve and opening G , the pressure was read on the mercury column, E. The e x p e r i m e n t s c o n s i s t e d simply in maintaining a c o n stant temperature in A as indicated by the thermocouple and read- g ing the vapor pressure o KandG on the appropriate inx Barher strument. Up to 161" C., where the vapor pressure is 3.85 atmospheres, measurements were made with the c o l u m n ; a b o v e this Figure 3-variation of LO^ of Vapor t e m p e r a t u r e up to Temperature Pressure with Reciprocal of Absolute 320.6' C. (the critical temperature), where the vapor pressure is 41.6 atmospheres, the piston gage was used. Table I contains the data. For completeness, vapor pressures below 1 atmosphere as determined by Barker (1) down to 0" C. have been included.
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For substances having a normal boiling point below about 150" C. the static or direct measurement seemed most simple and accurate. The pure substance was enclosed in a suitable container, heated to a known temperature, and the equilibrium pressure measured by suitable means. In this laboratory a mercury column 28 f e e t (8.54 m e t e r s ) long served for pressures up to about 10 atmospheres; above this pressure a deadweight p i s t o n gage was used. Figure 1 shows the Table I-Vapor Pressures of Toluene a t Different Temperatures TEMPERA- PRES- TEMPERA- PRES- TEMPERA- PRESapparatus diagramTURE SURE TURE SURE TUR3 SURE matically. R e d i s c. Aim. c. Aim. c. Afm. t i l l e d t o l u e n e was n 0.0093 186.5 6.12 257.2 17.69 0,0533 194.0 6.98 264.0 21.39 3 1 : 6 placed in the steel 0,202 203.5 8.26 279.5 24.81 62.0 0.533 214.4 9.89 280.0 25.10 89.7 bomb, A . The ca1.00 110.7 226.0 283,O 11.88 26.00 pacity of this bomb 234.5 301.5 129.5 13.25 1.68 32.40 246.0 320.0 149.5 16.00 41.48 2.80 was 50 cc.; the outside 250.0 161.0 17.06 3.85 320.6(ic) 41.60(Dc) diameter was 2 inches 253.5 175.5 17.46 5.18 (5 cm.), the length 8 i n c h e s (20 c m . ) . Figures 2 and 3 show the data graphically. I n Figure 2 Temp OC. This container. when the temperature is plotted against the pressure, and in Figure Figure 2-Variation of Vapor Pressure of assembled and con3 the reciprocal of the absolute temperature is plotted against Toluene with Temperature nected to the valve F. the log of the pressure. was placed in the copper casting, B, which fitted the bomb Literature Cited closely. Around this casting was wound a heating coil and O
1
Received October 10, 1929.
(1) Barker, Z. 9 h y s i k . Chem., 71, 235 (1910).
