30 CIRCULAR 6 3 5, U. S. DEPARTMENT OF AGRICULTURE 



Chemical tests have indicated that a l-iy 2 -2 formula (i. e., 1 

 pound of sodium cyanide, iy 2 pints of sulfuric acid, and 2 pints of 

 water) yields somewhat more hydrocyanic acid gas than the 1-1 1^-3 

 formula, but the larger quantity of water in the latter avoids danger 

 of crystallization of the residue in the containers and. is the most 

 practical for general use. 



From Calcium Cyanide 



Calcium cyanide is a granulated material packed in tin containers 

 of various sizes. When exposed to the air the granules absorb mois- 

 ture and a chemical reaction takes place which liberates hydrocyanic 

 acid gas. Strips of paper should be placed on the floor of the chamber 

 to be fumigated and on this the calcium cyanide should be spread, 

 about 9 square feet of floor space being allowed for each pound of 

 the material to be scattered. After the material is properly distrib- 

 uted, hydrocyanic acid gas is evolved rather rapidly, and the 

 operator must wear a suitable gas mask at all times when 

 applying it. 



The highest grade of calcium cyanide is reported to be equivalent 

 to 50 to 55 percent of hydrocyanic acid and the lower grades equivalent 

 to 23 to 29 percent. In practical fumigation work some of the hydro- 

 cyanic acid may be retained in the residue. For example, if the high- 

 grade material is equivalent to 50 percent of hydrocyanic acid, then 

 16 ounces would be required to produce a concentration of gas equiva- 

 lent to that of 8 ounces of liquid hydrocyanic acid. For the best 

 results the exposure should be 72 hours and the temperature of the 

 tobacco 70° F. or above. 



CARBON DISULFIDE 



Carbon disulfide is a colorless, volatile liquid, which evaporates 

 upon exposure to the air, forming a heavy gas toxic to stored 

 tobacco insects and human beings. Owing to the fire risk in- 

 volved, its use is greatly restricted in chamber fumigation. Ap- 

 proved gas masks should be worn by operators of fumigation 

 chambers in which this gas is used. 



In the fumigation of tobacco the liquid carbon disulfide is poured 

 into shallow metal pans suspended from the ceiling of the fumigation 

 chamber. The dosage recommended for stored tobacco is 10 pounds 

 of the liquid per 1,000 cubic feet of space, with an exposure of 72 

 hours. The temperature of the tobacco should be 70° F. or above for 

 the best results. The vapors of carbon disulfide are highly inflam- 

 mable and explosive, and this gas should not be used except in 

 accordance with the regulations of fire insurance underwriters. 



The following permit for the use of carbon disulfide as a fumigant 

 is endorsed by the Southeastern Underwriters' Association and the 

 Virginia Insurance Rating Bureau : 



In consideration of the following warranties, permission is hereby granted for 

 the keeping on premises and for the use of carbon disulfide as a fumigant or 

 insecticide. 



