26 BULLETIN 872, IT. S. DEPARTMENT OF AGRICULTURE. 



direction from which the wind is coming. After the preliminary 

 ventilation has been in progress for one or two hours, it is safe for 

 an operator to enter and open all windows and doors, but he 

 should not remain in the building until it has been thoroughly aired. 

 Specific directions as to the length of time for ventilation can not be 

 given to meet all cases. Much depends upon the movement of air 

 currents, the humidity of the air, and the rate of gas leaking from the 

 building during the hours of fumigation. To be absolutely safe, 

 buildings should be ventilated until there is no odor of gas before 

 persons are allowed to resume their work. Men accustomed to fumi- 

 gate soon acquire from experience knowledge which governs their 

 action in remaining in buildings during the period of ventilation. 



Procedure Afteb Ventilation. 



After the mill has been ventilated thoroughly an operator should 

 tour the building and make certain that no charge of cyanid was 

 overlooked in the dropping or that no charge failed to be lowered 

 into the generators if the stringing method was used. Any such 

 charges should be removed from the building and placed with the 

 stock of unused cyanid. Laborers should now be sent through the 

 building to remove the generators, dumping their contents into a 

 sewer or into a hole dug in the ground and giving the generators a 

 thorough washing. If the chemical action has been complete, the 

 residue in the jars after fumigation may not be particularly poison- 

 ous, 3 r et it is acid, and will burn clothing and skin, and should be 

 handled with care by reliable men. Men should be warned against 

 deliberately inhaling any fumes that may be given off by the residue, 

 either while they are removing the generators or emptying them. 

 Generators that begin to bubble when disturbed should be avoided 

 until the bubbling has ceased. When the residue has been absorbed, 

 after it has been poured in the hole in the ground, the soil should be 

 replaced. 



Efficiency of Fumigation. 



Experiments prove that in an air-tight chamber hydrocyanic-acid 

 gas will penetrate in killing concentrations to a depth of 3 inches, but 

 in mill fumigation the gas does not penetrate flour and mill products 

 much beyond 1 inch, and often, particularly near the floor, not even 

 that far. Not all mill pests are equally affected by the gas. In a mill 

 infested by the Mediterranean flour moth hydrocyanic-acid gas is a 

 very effective treatment. All stages of the moth, including the egg, 

 if not covered with more than 1 inch of flour, are killed, but upon the 

 several stages of the flour beetles, " bran bugs," and the cadelle the 

 gas treatment is of less value. Many of these pests hide in places 



