2.2.12. Boiling point
2.2.12. Boiling point
EUROPEAN PHARMACOPOEIA 5.0
Figure 2.2.11.-1. – Apparatus for the determination of distillation range
Dimensions in millimetres
adaptor. A thermometer is inserted in the neck of the flask
so that the upper end of the mercury reservoir is 5 mm lower
than the junction of the lower wall of the lateral tube. The
thermometer is graduated at 0.2 °C intervals and the scale
covers a range of about 50 °C. During the determination,
the flask, including its neck, is protected from draughts by
a suitable screen.
Method. Place in the flask (A) 50.0 ml of the liquid to be
examined and a few pieces of porous material. Collect the
distillate in a 50 ml cylinder graduated in 1 ml. Cooling
by circulating water is essential for liquids distilling below
150 °C. Heat the flask so that boiling is rapidly achieved and
note the temperature at which the first drop of distillate falls
into the cylinder. Adjust the heating to give a regular rate
of distillation of 2-3 ml/min and note the temperature when
the whole or the prescribed fraction of the liquid, measured
at 20 °C, has distilled.
Table 2.2.11.-1. — Temperature correction in relation to
the pressure
Distillation temperature
Correction factor k
up to 100 °C
0.30
above 100 °C up to 140 °C
0.34
above 140 °C up to 190 °C
0.38
above 190 °C up to 240 °C
0.41
above 240 °C
0.45
Correct the observed temperatures for barometric pressure
by means of the formula :
t1
=
the corrected temperature,
t2
=
the observed temperature, at the barometric
pressure b,
General Notices (1) apply to all monographs and other texts
k
=
the correction factor taken from Table 2.2.11.-1
unless the factor is given,
b
=
the barometric pressure, expressed in kilopascals,
during the distillation.
01/2005:20212
2.2.12. BOILING POINT
The boiling point is the corrected temperature at which the
vapour pressure of a liquid is equal to 101.3 kPa.
Apparatus. The apparatus is that used for Distillation Range
(2.2.11) with the exception that the thermometer is inserted
in the neck of the flask so that the lower end of the mercury
reservoir is level with the lower end of the neck of the
distillation flask and that the flask is placed on a plate of
isolating material pierced by a hole 35 mm in diameter.
Method. Place in the flask (A) 20 ml of the liquid to be
examined and a few pieces of porous material. Heat the flask
so that boiling is rapidly achieved and record the temperature
at which liquid runs from the side-arm into the condenser.
Correct the observed temperature for barometric pressure
by means of the formula :
t1
=
the corrected temperature,
t2
=
the observed temperature at barometric
pressure b,
k
=
the correction factor as shown in Table 2.2.11.-1
under Distillation Range,
b
=
the barometric pressure, in kilopascals, at the
time of the determination.
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