Vapor-Pressure Chart for Volatile Hydrocarbons Page: 2
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I.C. 7215
under the direct supervision of Kenneth Eilerts, physical chemist, and R. E.
Heithecker, senior petroleum engineer, Bureau of Mines, Bartlesville, Okla.
The va.por-pressure chart was prepared by S. B. Thomas. The manu-
script was read and criticised by the following members of the Bureau of
Mines: E. S. Burnett, C. B. Carpenter, Kenneth Eilerts, H. C. Miller, M. A.
Schellhardt, and Gustav Wade. To them the writer is deeply indebted.
DISCUSSION OF VAPOR PRESSURE
When the vapor of a single component liquid is exposed to "free" space
above it there is a continuous movement of the molecules of the liquid from
the surface of the liquid into the "free" space, and. at the same time a
continuous passing of molecules of the vapor into the liquid. If these two
phenomena exactly balance one another, the liquid and its vapor will be in
equilibrium, and the vapor will be saturated with liquid. The resultant pres-
sure exerted by the saturated vapor is known as its vapor pressure.
Vapor pressures of single component liquids are independent of the
quantities of vapor or liquid in equilibrium but vary with temperature, and
for every temperature below the critical pressure a definite pressure is
exerted by a vapor in equilibrium with liquid.
Many vapor-pressure charts have as their basis the coorCdinates
(logarithm of vapor pressure and reciprocal of absolute temperature) sug-
gested by an integrated form of the Clausius-Clapeyron equationV, which
is as follows:
A
logp = - T + B,
where p = vapor pressure,
T = absolute temperature, and
A and B = constants.
Experimental data, however, do not yield straight lines when plotted upon this
basis but yield curves in which the curvature is small throughout their extent.
Consequently, the logarithm of pressure and the reciprocal of absolute term-
perature were chosen as coordinates for a convenient graphic means for
presenting data on vapor pressures of hydrocarbons.
A vapor-pressure chart using a special nonuniform temperature scale
has been suggested by Cox (16) in an effort to present vapor-pressure data as
4/ A derivation of the equation is given by Getman and Daniels (22).8848
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Smith, R. Vincent. Vapor-Pressure Chart for Volatile Hydrocarbons, report, August 1942; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc67019/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.