36 



CIRCULAR 369. U. S.'DEPT. OF AGRICULTURE 



runs through this steam-heated tank and is so designed that the 

 fumigant is in gaseous form by the time it reaches the vacuum 

 chamber. If carbon disulphide is used, a specially designed vapor- 

 izer is required, since it must be mixed with carbon dioxide before 

 it is admitted to the fumigating chamber. 



In some modern vacuum outfits an accumulator tank is utilized to 

 vaporize and heat the fumigant before drawing it into the vacuum 

 chamber. It consists of a tank with a heating coil into which the 

 dosage is drawn, and in which it can be held until ready for use. 



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Figure 31. — End view of vacuum equipment shown in figure 30. Tank at left closed and 

 under fumigation. Tank at right nearly loaded with 43,000 pounds of Turkish 

 tobacco. These tanks will treat all incoming tobacco placed in this storage establish- 

 ment. Note end of cylindrical accumulator on top of tank at right. . 



Hydrocyanic acid, chloropicrin, and mixtures of carbon dioxide 

 with ethylene oxide, methyl bromide, methyl formate, and carbon di- 

 sulphide are used in vacuum fumigation. The dosage required de- 

 pends on the type and quantity of the commodity to be fumigated, its 

 temperature, and the length of exposure. 



PROCEDURE 



The commodity to be fumigated is loaded into the vacuum tank, 

 the doors are closed, and air is removed until the vacuum gage regis- 

 ters 28 or 29 inches. The proper dosage of fumigant is then admitted 

 through the vaporizer or accumulator. 



If the tank is equipped with multiple gas inlets and a gas-circu- 

 lating system, the fumigant should be pumped from the accumulator 

 tank into the vacuum tank through the circulating system. When 

 all the fumigant is in the tank, the valve to the accumulator tank 



