JOURNAL OF CHEMICAL EDUCATION
DISTILLATION BUBBLER S. HORWOOD TUCKER University of Glasgow, Glasgow, Scotland
SUPERHEATING, with the attendant danger of humping and frothing over, is a common occurrence during distillation; it has always to he anticipated and allowed for. Devices to this end are numerous: porous or even anthracite chips, platinum, glass wool, capillary tubes, an air-leak through a capillary tube, all provide the necessary points at which air bubbles can form and promote active ebullition. A form of bubbler which possesses several advantages can he easily made by any student with a rudimentary knowledge of glass blowing as follows. A piece of glass
B
C Pigure l
D
E
tubing is sealed a t one end, no effort being made to thin out the terminal lump of glass (A). A bulb is now blown a t this sealed end by heating the glass until the walls of the tube partially collapse and thereby thicken, followed by gentle blowing. A second bulb is now blown just above the first (B), and then the two are melted in the flame and merged into one bulb in the usual way, the thick end o'f glass being still retained (C). The thick end is now heated in the tip of the blow-pipe flame until red hot, time being allowed for the thinner parts to cool somewhat, and then the thick end is sucked in bv means of the mouth until a hemispherical cup is forked (D). The'upper end of the tube is then drawn off into a hook (E), not a loop, since removal of the bubbler from the distillation flask by means of a hooked copper wire is much more expeditiously accomplished when the tube has a hook than when it has a closed loop. The bubbler is inserted into the flask with hook uppermost and should he of such a length that the top rests in the neck of the flask. To accommodate flasks of different sizes bubblers of various lengths should he available. For large flasks the bubblers may conveniently he made of large tubing. Although primarily for use during distillation under ordinary atmospheric pressure the bubbler has been found to he efficient under reduced pressures if a few strands of fibre glass are added. The fine threads of glass probably function per se in preventing humping; but, furthermore, by winding themselves around the bubbler, they hold it down and, even if some humping occurs, prevent breakage.
OCTOBER, 1949
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