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BELL SYSTEM TECHNICAL JOURNAL 



entire process as safe as possible from the hazards that are always 

 present when using a solvent such as acetone. 



Fig. 8 illustrates the general arrangement of the equipment. Two 

 buildings are used instead of one to separate the large quantities of 

 solution present in the mixing room from the room in which the coating 

 machines with their electrical equipment are located. The acetone is 

 pumped from the underground storage tanks to the mixers. The cellu- 

 lose acetate is weighed out from bins and added to the mixers and the 



TO ACETONE 



■CONCENTRATION 



RECORDER 



TO RECOVERY 

 PLANT 



EXPLOSION 

 VENTS 



SECTION A-A 



Fig. 7 — -Schematic view of one coating head. 



whole stirred for se^■eral hours until fully dissolved. One gallon of 

 acetone is used to ten ounces of cellulose acetate. The solution is then 

 pumped continuously from the mixers to the machines. From the 

 machines it flows to a sump by gravity and from the sump is forced 

 back to the mixers. The reasons for circulating the cellulose acetate 

 solution are to keep it homogeneous, to keep the amount of solution 

 in or near the machines as small as possible, and to permit control 

 and maintenance of its viscosity at one location instead of in the indi- 

 vidual dope pots. 



