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4.5 DETERMINATION OF BOILING RANGE (DISTILLATION RANGE) 

      The boiling range is the temperature interval, corrected for a pressure of 101.3 kPa (760 Torr), within which a liquid, or a specified fraction of a liquid, distils in the following conditions.

Apparatus

      The apparatus (Fig. 1) consists of a distillation flask (A), a straight tube condenser (B) which fits onto the side arm of the flask and a plain-bend adaptor (C) attached to the end of the condenser. The lower end of the condenser may, alternatively, be bent to replace the 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 0.2ºintervals and the scale covers a range of about 50º. 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 150º. 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 to 3 ml per minute and note the temperature when the whole or the prescribed fraction of the liquid, measured at 20º, has distilled.

      Correct the observed temperatures for barometric pressure by means of the formula:

t₁ = t₂ + k (101.3 – b),

where t₁ = the corrected temperature,

t₂ = the observed temperature,

k = the correction factor taken from Table 1 unless the factor is given, and

b = the barometric pressure, expressed in kilopascals, during the distillation.

Table 1 Temperature Correction in Relation to the Pressure