26 CIRCULAR 8 6 9, U. S. DEPARTMENT OF AGRICULTURE 



hydrogen cyanide. The operator should wear a gas mask with a 

 suitable canister, and leave the chamber as quickly as possible 

 after scattering the discoids. This is a dangerous operation and 

 should not be undertaken by an inexperienced person. 



If hydrogen cyanide is used, the dosage should be at least 16 ounces 

 per 1,000 cubic feet, and as much as 24 ounces may sometimes be used 

 to advantage. The exposure should be 72 hours. If acrylonitrile- 

 carbon tetrachloride is used, the amount should be 32 to 40 ounces 

 per 1,000 cubic feet with an exposure of 72 hours for flue-cured 

 tobacco in hogsheads. For bales of Turkish tobacco and for bales or 

 cases of cigar filler or binder tobacco, 32 ounces with an exposure of 

 48 hours has proved satisfactory. All dosages given are to be used 

 at a temperature not lower than 70° F. 



In the fumigation of tobacco in atmospheric chambers, bales and 

 cases should be stacked with slats between them and with air spaces 

 on all sides to permit the gas to penetrate the tobacco. Better pene- 

 tration is usually obtained in atmospheric-chamber fumigation than 

 in warehouse fumigation. However, fumigation is not so effective 

 in atmospheric chambers as in vacuum chambers. 



Vacuum Chamber 



The fumigation of tobacco in partial vacuum is the most effective 

 method known for destroying insect infestations. When properly 

 performed it should kill all stages of the cigarette beetle and the 

 tobacco moth, at all depths in the tobacco (fig. 19) . Vacuum chambers 

 are expensive, but they are extensively used because of their efficiency 

 and the rapidity with which they can be operated. 



Figure 19. — Perforated capsules containing cigarette beetle larvae or eggs that 

 were placed in the cigars at the time of manufacture to test the effectiveness of 

 fumigation. 



