INDUSTRIAL FUMIGATION AGAINST INSECTS 



23 



1,000 cubic feet. Allowance is made for the fact that the fumigator 

 is constantly moving away from the discoids and that the full quan- 

 tity of the gas is not given off immediately. If the discoids are 

 chilled before being used, the concentration to which the fumigator 

 is exposed will be less. 



From the foregoing data it is evident that, where large quantities 

 of discoids are used, the fumigating crew must be large enough so 

 that the distribution of the fumigant will be speedy and no one man 



Figuke 20. — Man, protected by gas mask, removing the top from a tin can contain- 

 ing discoids impregnated with liquid hydrocyanic acid. 



is exposed to the gas for a dangerously long period. The use of this 

 material is not recommended for any but professional f umigators. 



DISPOSING OF SPENT DISCOIDS 



When the fumigation is finished and the building has been well 

 ventilated, the spent discoids and the empty cans can be gathered up 

 and thrown away. At the end of a 24-hour fumigation the discoids 

 will retain not more than a trace of hydrocyanic acid. 



THE POWDER METHOD 



Calcium cyanide in dust form is used in much the same way as the 

 discoids. On exposure to the air the powder absorbs moisture and a 



