INSECT CONTROL IN FLOUR MILLS. 25 



been arranged, the generators should be placed and the water and 



acid added. Each generator should then be moved at least 2 feet 



away from where the cyanid will be suspended. Men should then 



go through the mill, tying firmly the sacks of cyanid to the strings, so 



that they will hang suspended about 2 or 3 inches above the tops of 



the generators. This done, the generators are placed beneath the 



suspended sacks. All persons should then leave the building. One 



man can now pass from the top to the lower floors lowering the 



cyanid into the generators by the simple manipulation of the central 



cord at the exit of each floor. The basement charge should, of course, 



be lowered last, and preferably by means of a cord running to the 



outside mill door or to the outside through some slight opening about 



a window. 



Closing Buildings and Guarding Dooes. 



After the last charge has been set off and the last person has left 

 the building, the door or doors used as exits should be locked. If 

 such doors do not fit tightly, it will pay to paste strips of paper about 

 their edges. Guards should be placed about the building in such a 

 manner as to prevent persons entering the building. Guards should 

 not stand where they can smell any amount of escaping gas. There 

 should be several guards who keep in touch with one another, espe- 

 cially during the first one or two hours after the generation of gas. 



Time to Fumigate and Length of Exposure. 



Fumigate only during calm weather. During high winds the gas 

 is carried to one side of the room or building and, unless the building- 

 is very tight, it is dissipated more quickly. Experiments have proved 

 that insects are not active at temperatures lower than 50° to 60° F. 

 and are not then so easily killed by the gas. Best results follow fumi- 

 gations when the temperature is 70° F. or above. Everything for 

 fumigation should be in readiness before dark. When possible the 

 best time to fumigate is from Saturday afternoon to Sunday evening 

 or Monday morning. At this time fewer people are about. The 

 buildings should be allowed to remain closed for fumigation not less 

 than 12 to 18 hours, though exposures of from 24 to 36 hours, when 

 the building is tight and time is not an important factor, may effect 

 a better killing of pests. 



• Ventilation. 



Several hours should elapse after a mill has been opened for venti- 

 lation before laborers are allowed to enter for regular work. The 

 doors and the windows should be opened from without, according to 

 provision made before fumigation. In opening windows and doors, 

 open first those on the side of the building opposite to the 



