2. The Clarke-Rahrs methyl ester column
2 is illustrated in
.htmFig. 20.
A is the stopcock, above which the aqueous phase collects and is drawn off as necessary.
B is a standard-taper ground joint;
C is a
trap whose outside diameter is 12 mm. At
D the space between the consecutive bubblers is shown.
E is the thermometer tube, set in at an angle of about 45°; it carries a piece of rubber tubing
H which holds the thermometer.
F is a solid spot in the top return tube
only, where that tube has been sealed off; the apparatus will not function without this seal. It should be pointed out that the upper ends of all the return tubes should terminate just above the bends, as shown at
J; otherwise there will be too great a pressure due to the height of the liquid. The overall length as given is not critical.
4. A tarry residue of
10–17 g. is obtained. If an efficient column is not used in the distillation, the fore-runs will contain
5–10 g. of recoverable ester. The yield given is the total yield.