38 MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



of apparatus similar to that shown in figure 10. The apparatus should 

 be used only under a fume hood. 



All connections and stoppers used in this set-up should be of glass; 

 rubber and cork generally contain extractable substances which tend to 

 discolor the monomer or interfere with its polymerization. For the 

 same reason the use of stopcock grease and other lubricants, with the 

 exception of those consisting of silicone material, should be avoided for 

 joints exposed to the monomer or its vapor. 



For the purpose of heating the monomer to vaporize it, a retort heater 

 or heating mantle as indicated in the diagram is preferable. If one is 

 not available, however, an electric hot plate will serve satisfactorily 

 if a sand or water bath is used with it to distribute the heat evenly over 

 the lower surface of the retort flask. The hot plate should have ad- 

 justable heat control and must be of the enclosed element type to avoid 

 undue fire hazard. Gas burners or other open-flame heat sources should 

 never be used in this connection. 



If distillation is to be carried out at full atmospheric pressure, the 

 receiving flask must be provided with a relief vent in place of the vacuum 

 connection. This vent should be loosely packed with soft paper or cello- 

 phane to allow equalization of pressure without undesirable escape of 

 vapor. When the monomer is distilled under full atmospheric pressure 

 it may show a tendency to polymerize in the retort flask because of the 

 higher temperature required for keeping the liquid boiling under these 

 conditions. This can usually be prevented by putting a small addi- 

 tional quantity of hydroquinone into the retort flask to increase the 

 inhibitor concentration. One-tenth of a gram per liter should be suffi- 

 cient for this purpose, and it is not necessary to add any in subsequent 

 lots if the residue is left in the flask after the first run. 



The general procedure for carrying out the distilling operation follows: 



1. After making sure the apparatus is clean and dry throughout, set 

 it up in a fume hood or other enclosure where all escaping vapor will be 

 effectively prevented from diffusing into the room. 



2. Pour into the retort flask inhibited monomer until the flask is 

 nearly half full. 



3. Start the cold water circulation in the condenser jacket. 



4. Turn on the aspirator pump and adjust the flow of water through 

 it to maintain a vacuum of approximately 200 millimeters in the system. 



5. Turn on the retort heater and regulate it to keep the monomer 

 in the retort flask boiling gently. 



6. Replenish the supply of monomer in the retort flask, preferably 

 just before the flask becomes empty. 



7. Empty the receiving flask at sufficiently frequent intervals to 

 prevent overflow into the vacuum line. Pour the distilled monomer 

 from this flask into clean dry bottles, fitted with metal-lined screw-caps, 

 or into flasks stoppered with tinfoil-wrapped corks. Store this inhibitor- 

 free monomer at a reduced temperature of 4° C. (approximately 40° F.) 

 or lower. 



8. Take the apparatus apart and allow the monomer to evaporate 

 completely from all joints in order to eliminate the possibility of their 

 "freezing" in place as a result of polymerization. The packed column 

 and the retort flask should be rinsed with a solvent, such as acetone, or 

 toluene to which a little denatured alcohol has been added, in order to 

 remove any partial polymer that may tend to adhere to them. 



