Precision fractional distillation under diminished pressure

PRECISION FRACTIONAL DISTILLATION UNDER DIMINISHED PRESSURE 

An elementary account of the subject has been given in the previous Section. For the fractional distillation under diminished pressure of liquids differing only slightly in boiling point, a fractionating column (see Sections 11,15 and II, 17) must be used. Provision must, of course, be made for the insertion of a capillary tube into the flask containing the mixture. This can be done by any of the following methods — 

If a bolt-head flask is used and a rubber stopper is permissible, there is ample room for the insertion of a capillary tube and the fractionating column in the wide neck. 

A flask is provided with a long side neck (Fig. II, 25, 1) through which a capillary is inserted and attached externally by a short length of rubber pressure tubing. With this type of connexion there is essentially no contact of hot vapours with the rubber and little or no contamination results. The neck of the flask is preferably fitted with a standard ground joint if attack of the organic vapours on the rubber stopper is likely to occur. 

A two-necked flask (compare Fig. II, 56, 13), with the wide neck for the fractionating column and the small neck for the capillary tube, is widely employed. 

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PRECISION FRACTIONAL DISTILLATION UNDER DIMINISHED PRESSURE... 

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