EEPLACEMENT OF THE HYDROXYL GROUP OF ALCOHOLS 73 Various mechanical means of providing a constantly renewed surface have been proposed, 66-66 of which the following one is simple and efficient. 67 The apparatus shown in Fig. 2 is constructed from brass tubing with silver soldered joints. One arm of the U-shaped vessel is closed by a rubber stopper which supports the fluorine inlet tube, as indicated in the drawing. The rubber stopper is protected on the inside by a covering of thin copper foil, and, in case of a too sudden reaction, functions as a safety valve. In use, the vessel is filled up to the hori-zontal division. The stirrer then acts as a pump to force a rapid counter-current flow of liquid along the horizontal section which divides the lower part of the vessel. Fluorine is passed in through a roll of copper gauze, and temperature control is obtained by surrounding the reaction vessel with a suitable bath.
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