28 CIRCULAR 635, U. S. DEPARTMENT OF AGRICULTURE 



operation should protect themselves against possible gas pockets by 

 wearing approved gas masks. The liquid hydrocyanic acid is applied 

 through a piping system similar in design to that described above 

 for closed warehouses. Slats should be placed between the stacked 

 bales of tobacco for the duration of the fumigation period so that 

 the maximum penetration may be obtained. Dosages below 16 ounces 

 per 1,000 cubic feet are not recommended for gaslight chambers. 

 When tobacco is heavily infested and several inches of penetration 

 is desired, a dosage of 24 ounces should be applied. The exposure 

 should be 72 hours for all types of unmanufactured tobacco, and the 

 best results are obtained when the temperature of the tobacco is 70° 

 F. or above. 



From Sodium Cyanide and Sulfuric Acid 



Hydrocyanic acid gas can also be generated from sodium cyanide 

 and sulfuric acid by the barrel or pot method. For mixing the 

 materials the most satisfactory formula is as follows : Sodium cyan- 

 ide (96 to 98 percent) 1 pound, sulfuric acid (commercial grade, 66° 

 Baume) 1% pints, and water 3 pints. 



The required quantity of water should be placed in the barrel or 

 crock first, after which the sulfuric acid should be poured into the 

 water with care. The charge of sodium cyanide for each container 

 should be placed in double thicknesses of paper bags and put beside 

 the container before the fumigation is begun. When sealing is com- 

 plete and the chamber vacated, the bags of cyanide are placed in the 

 acid-water mixture. The operator should wear a gas mask with 

 suitable canister for protection against hydrocyanic acid gas and 

 should leave the fumigated space and immediately seal the exit 

 from the outside. All entrances to the warehouses should be 

 securely locked to prevent the entry of persons who may not know 

 of the danger. (See figure 21.) 



In crocks not more than 4 pounds of sodium cyanide is used for 

 each fumigation and in barrels (fig. 21) not over 30 pounds. Sodium 

 cyanide in 1-ounce egg-shaped balls is equivalent to about 53 percent 

 of hydrocyanic acid, but this figure may be reduced as much as 10 

 percent because of the retention of a portion of the gas by the acid 

 residue. Under practical conditions, therefore, the yield of hydro- 

 cyanic acid gas is only about 43 percent of the weight of sodium 

 cyanide used, and the dosage should be calculated on the basis that 

 2!/2 pounds of sodium cyanide will yield the equivalent of 1 pound 

 of commercial liquid hydrocyanic acid. The volume of space to 

 be fumigated should be computed in cubic feet and a sufficient number 

 of generators placed to accommodate the sodium cyanide required for 

 the fumigation. 



When the fumigation is completed and the chamber thoroughly 

 ventilated, the liquid residue in the barrels or crocks must be 

 disposed of promptly. When the generator is moved and the 

 liquid residue shaken about, a small amount of hydrocyanic acid 

 gas may be given off, and it is necessary for operators to avoid 

 breathing this gas. The liquid residue should be buried beneath 



