MIL-DTL-38219D(USAF)
APPENDIX A
A4.3 Procedure
a. Sample preparation
(1) Transfer 600 mL of the sample into a large separatory funnel.
(2) Shake the funnel for 1 to 2 minutes and then let contents settle for 15 to 20 minutes.
(3) Draw off lower 100 mL of fuel and discard.
b. Assemble apparatus in accordance with figure A2.
c. Place 300 mL of the prepared sample in the 500-mL flask.
d. Place ice around cold finger in the Dewar flask.
e. Begin the stirring action and carefully evacuate the system to degas the sample. The system shall be
evacuated at ambient temperatures for a period of 10 minutes.
f. Control of temperature and pressure
(1) Slowly increase the temperature of the contents of the flask by varying the powerstat.
(2) At no time shall the sample be allowed to bump the flask or boil up into the condenser.
(3) If the magnetic stirrer makes a thumping sound, an indication of too rapid increase in
temperature, reduce the setting of the powerstat.
(4) A bleed valve is provided so that a continuous, stable vacuum is maintained.
(5) With proper adjustment of temperature and pressure, a reflux action is noted within the neck
of the condenser. (Refluxing shall be to the same height for each run.)
(6) When refluxing reaches an equilibrium at this level, the temperature of the reflux vapor will
agree within 4°C of the liquid.
(a) If the two temperatures do not agree within 4°C, change the system pressure, increase
temperature, and repeat temperature-pressure measurements until stable reflux conditions
are met.
(b) Stable reflux conditions shall be those where the temperatures, pressure, and height
of reflux in the condenser do not change on three successive readings at 3-minute
intervals.
g. Change the system pressure, increase the temperature, and repeat the temperature-pressure
measurements over the entire pressure range up to atmospheric pressure. A minimum of four stable reflux conditions
(boiling points) shall be obtained.
h. Record the temperature of the liquid, temperature of the vapor, and pressure of the system at stable
reflux conditions.
i. Correct the pressure as shown by the manometer for variations in barometric pressures.
j. Allow the fuel to cool to ambient temperature and pressure.
k. Remove sufficient fuel from the flask and perform distillation according to ASTM D86.
A4.4 Calculations
A4.4.1 Report of results
a. Plot on semilog paper the reciprocal of absolute temperature on the abscissa versus the log of vapor
pressure in psi on the ordinate for each boiling point.
b. Draw a smooth curve through the boiling points obtained, and extend the lines slightly at each end.
c. Report the results of corrected vapor pressure as determined by the vapor reflux method from the
prepared graph at desired temperature.
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