36 



CIRCULAR 3 6 9, U. S. DEPARTMENT ■ OP AGRICULTURE 



29 inches is drawn. The proper dosage of f umigant is then admitted 

 through the vaporizer or accumulator. The remaining vacuum 

 should be held without change for the duration of the fumigation, 

 since it. has been found that better results are obtained if the vac- 

 uum is held instead of being broken with air. A chart record (fig. 

 34) should be made of each fumigation in case it is needed for 

 future reference. 



At the end of the fumigation the gas is pumped out of the cham- 

 ber and the vacuum is broken with air. If desired, the fumigated 



Figure 33. — Portion of vacuum fumigator installed in a large candy establishment. 

 Note vacuum pump in left foreground ; cylindrical accumulator on tank ; gages for 

 automatically recording pressure, vacuum, and temperature ; and cylinder of the 

 ethylene oxide-carbon dioxide mixture in front of operator. Cylinders of methyl 

 formate-carbon dioxide mixture are attached in the same manner. 



products can be " air-washed " several times by alternately drawing 

 and breaking a vacuum of about 27 inches. 



Commodities taken from cold storage should be allowed to come 

 up to room temperature before they are loaded into the vacuum 

 tank. Insects that have been chilled, are in a dormant state, and 

 their resistance to fumigants is increased. This resistance is re- 

 tained for several hours after they are brought into a heated atmos- 

 phere, and is therefore not overcome during the time they are in 

 the heated vacuum chamber. If the infested commodities are 

 allowed to warm up to room temperature before fumigation, the 

 insects will regain their normal activity and lose their resistance 

 to fumigants. 



