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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. 31