Micromethod for Determining Boiling Points of Liquids at Different Pressures EDWIN E. HAYS, F. W. HART, AND R. G.GUSTAVSON, University of Denver, Denver, Colo.
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pressure may be varied and observed. A small capillary tube sealed about 7 mm. from the open end is placed in the liquid. The authors have found it convenient to blow a slight bulge near the bottom of the tube for the capillary tube to rest in. The bulb of the thermometer is immersed in the liquid in the test tube, which is surrounded by a system of brass baffle plates as shown. This baffle system has been found to be very important if accurate results are to be obtained. The bottom baffle plate holds the test tube in place. The pressure is increased by use of a small baumanometer bulb and low pressures may be obtained in any convenient fashion. Pressures are read on the mercur barometer on a meter stick, which is adjustable by means o?a screw. The bath is heated until there is a rapid evolution of bubbles at the pressure desired, and then allowed to cool. The temperature at which the liquid starts t o rise in the capillary tube is taken as the boiling point. As soon as this temperature is reached the pressure and temperature are recorded. The pressure is then reduced about 10 cm. immediately, causing a further rapid evolution of bubbles. The liquid is again allowed to cool until the liquid rises in the capillary tube and the temperature and pressure are again noted. I n this way a vapor pressure curve may be obtained in a very short time.
HAND BULB
Figure 2 shows t h e vapor pressure curve for water as determined and as given in t h e literature. Table I records boiling points for sea level as determined at Denver for ten common organic liquids, together with boiling points recorded by Kamm (1). The boiling point of ethyl oxalate at 10 mm. is also included. All t h e temperatures are uncorrected.
FIGURE1. DIAGRAM OF APPARATUS
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44BORATORIES located a t altitudes other than sea
level have difficulty with courses in qualitative organic analysis because in standard reference works boiling points of most organic compounds are given only for sea-level conditions. This has been the experience in Denver, where the barometric pressure varies between 623 and 631 mm. The authors have been successful in designing an apparatus for obtaining boiling points for pressures between 900 and 10 mm. with sufficient accuracy for t h e purposes of qualitative organic analysis. Figure 1 shows the design of the apparatus used.
TABLE I. BOILINQ POINTDETERMINATIONS
A small test tube 9 by 70 mm., containing a few drops of the liquid to be tested, is enclosed in a closed system in which the
Compound
Experimental
Ethyl iodide n-Amyl alcohol Methyl acetate %-Butyl carbonate Ethyl acetate, n-Amyl chloride o-Chlorophenol E t h 1 carbonate Cargon disulfide Chloroform Diethyl oxalate
72.5 137 57 206.5 77 108.2 174.5 126.5 47 61.6 75
Literature
c.
c.
72 137 57 205 77 108 176 126.0 46 61 72-74
Pressure
Mm. 760 760 760 760 760 760 760 760 760 760 10
The bath liquids in Table I1 have been found suitable for t h e indicated temperatures and pressures.
0 0
9 TABLE11. BATHLIQUIDS Maximum Temperature
$8 2-
22
c.
Mineral oil (Squibb’s) Glycerol
150 260 150 250
Pressure Mm. Ha 10 760 20 780
0
g?
Literature Cited (1) Ksmm, O., “Qualitative Organic Analysis,” 2nd ed., N e w York, John Wiley & Sons, 1932.
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83
p“ $
EXP ERIUENTAL
R E C ~ I Y EMarch D 21, 1936.
--L / TERATURE
95 100 /os DEGREES CENTIGRADE FIGURE 2. VAPOR-PRESSURE CURVE 90
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