54 CIRCULAR 369, IT. S. DEPT, OF AGRICULTURE 



LOCAL FUMIGATION 



A general fumigation once or twice a year does not entirely solve 

 the insect problem in a flour mill, since small infestations are con- 

 tinually developing here and there throughout the milling system. 

 Many millers guard against these infestations by establishing a 

 regular schedule of local fumigations, or treatment of individual 

 machines. Local fumigations can be conducted on . week ends or 

 any night after the mill is shut down. Chloropicrin, hydrocyanic 

 acid, and the ethylene dichloride-carbon tetrachloride mixture are 

 used extensively for this purpose. 



Fumigation With Chloropicrin 



Chloropicrin is used in local fumigations in the same way as de- 

 scribed for general fumigations, except that the individual machines 

 are sealed off from the others. The fumigator should, of course, 

 wear a gas mask. 



Fumigation With Ethylene Dichloribe-Carbon Tetrachloride Mixture 



The ethylene dichloride-carbon tetrachloride mixture is applied 

 by spraying or pouring it into the individual units at the following 

 dosages : 



Purifier and reels 16 to 29 ounces in each conveyor. 



Sifters 12 ounces in each section. 



Flour conveyors 1 to 2 ounces per linear foot. 



Elevator boots 12 ounces. 



Elevator heads 12 ounces to each leg. 



Other machinery in proportion to size. 



Fumigation With Hydrocyanic Acid 



Hydrocyanic acid can be applied in several different ways. The 

 same safety precautions should be taken as in a general fumigation. 

 Workmen handling the material should be equipped with gas masks 

 and all others kept out of the mill. 



The machines should be prepared by cleaning out all accumula- 

 tions as outlined in the directions for preparing a mill for a general 

 open-space fumigation. Machines treated separately should be sealed 

 off and made as tight as possible. 



Calcium cyanide containing 22 to 28 percent of available hydro- 

 cyanic acid is frequently used for this purpose and is easily applied. 

 A dosage of about 12 ounces for each machine is applied to rolls, 

 purifiers, and sifters. It is spread evenly on dry newspapers in the 

 lower part of the machine. If sifters are equipped with blanks, 

 they should be removed from one section or opening to allow free 

 circulation of the gas. All machines should be made as tight as 

 possible, sheets of wrapping paper being placed behind the ventilat- 

 ing doors on the sides of the purifiers. Each elevator leg should 

 be treated with 2 ounces of the calcium cyanide. 



Calcium cyanide containing 51 to 52 percent of available hydro- 

 cyanic acid is also used for local fumigation work and is applied by 

 means of the special apparatus illustrated in figure 41. This ma- 

 chine draws in calcium cyanide dust through a blower intake, mixes 

 it with air and moisture, and blows the liberated hydrocyanic acid 



