32 CIRCULAR 3 6 9, U. S. DEPARTMENT OF AGRICULTURE 



piping system with one or more spray nozzles can be installed (figs. 

 17, 18, and 23). 



Use of Fumigants Suitable Also for Large Spaces 



Hydrocyanic acid, chloropicrin, methyl bromide, and mixtures of 

 carbon dioxide with ethylene oxide and methyl formate are all suitable 

 for vault fumigation, and they can be used in the manner described 

 for the fumigation of large spaces. The method selected for gener- 

 ating hydrocyanic acid will depend largely upon the preference of 

 the operator. Any of the previously described methods is suitable. 

 If calcium cyanide is used, it can be sprinkled in a thin layer on a 

 strip of paper laid on the floor or on shelves built for the purpose. 

 Chloropicrin can be applied by pouring the dosage into the evapo- 

 rating pan or by forcing it in through a piping system with compressed 

 air. The mixtures of ethylene oxide and methyl formate with carbon 

 dioxide are applied through a piping system and can be administered 

 by connecting the cylinder to the system (fig. 23) and opening the 

 valve. If the cylinder is placed on a platform scale, it is an easy 

 matter to let in the quantity desired. 



Use of Other Fumigants 



Various other fumigants, not suitable for warehouse fumigation, 

 can be used successfully for vault fumigation. They are carbon 

 disulfide, ethylene oxide, ethylene dichloride-carbon tetrachloride, and 

 carbon tetrachloride. 



CARBON DISULFIDE 



Carbon disulfide is a colorless, volatile liquid, which boils at 114.8° F. 

 On exposure to air it evaporates, forming a heavy vapor that is very 

 toxic to insects. 



It is applied by pouring the liquid into the evaporating pan of a 

 vault at the rate of about 5 pounds per 1,000 cubic feet of space. If 

 the vault is not tight or if highly absorbent commodities are being 

 treated, the dosage should be increased proportionately. It is not un- 

 common to use from 20 to 30 pounds per 1,000 cubic feet. 



Unfortunately, the value of carbon disulfide as a fumigant is greatly 

 limited owing to the highly inflammable nature of its vapors, which 

 restricts its use to situations where the fire hazard can be effectively 

 controlled. In admixture with air the vapors, which are both in- 

 flammable and explosive, may ignite from fire or even without the 

 presence of flame at temperatures of 212° F. or above. Fire insurance 

 is void while carbon disulfide is being used. It should be remembered 

 that lighted lanterns, cigars, pipes, cigarettes, pilot lights in gas stoves ^ 



and heaters, sparks from electric switches, static or frictional elec- 

 tricity, sparks caused by hammering on metal, and even hot steam 

 pipes may cause an explosion of the vapor. For this reason carbon 

 disulfide should be used only where the fumigation vault is isolated 

 from other buildings and the fire hazard can be controlled. 



Mixtures of carbon disulfide with other chemicals, such as carbon 

 tetrachloride and sulfur dioxide, for the purpose of reducing the fire 

 hazard are now on the market. 'Although not absolutely noninflam- 

 mable, they can be usee} with comparative safety. Their efficacy is 



