at least about 10 minutes preferably about 12 to about 90 minutes the resulting mixture will be less tacky and less susceptible to crystallization of the components with storage a recirculating apparatus for the thermal dimerization of allene was designed as follows the heated reactor was a bank of approximately 110 segments each about 30 cm long of stainless steel tubing 1 27 cm in outside diameter the segments were arranged vertically in series and connected to one another by u shaped stainless steel connectors to which they wer welded the volume of the heated portion of the reactor was about 3 4 liters the bank of tubes was immersed in a fluidized bed of aluminum oxide particles thermocouples wedged between the connectors of the reactor at various points allowed one to monitor the wall temperature of different segments of the reactor downstream from the reactor was a cold trap containing a cooling fluid at approximately 65 u00b0 c above a flask which functioned as a gas liquid separator downstream from the first trap was a second trap filled with dry ice in dichloromethane guarding the outlet to the system through an oil bubbler to condense any allene which otherwise could have escaped from the system.