24 



CIRCULAR 3 6 9, IT. S. DEPARTMENT OF AGRICULTURE 



chemical reaction takes place by which hydrocyanic acid gas is 

 given off. 



APPLYING THE POWDER 



The required number of cans of calcium cyanide are distributed 

 throughout the building. They are then opened and the contents 

 scattered over the floor in a layer not more than half an inch thick. 

 To facilitate removal of the dust after the fumigation, it may be 

 scattered on strips of paper previously laid on the floor, although it is 

 sometimes placed directly upon the floor (fig. 21). Each can of 

 fumigant is equipped with a special perforated top, which the fumi- 

 gator puts in place of the friction top when he is ready to use it. 



Inasmuch as the gas is given off very rapidly after the dust is 

 exposed to the air, the fumigator should wear a gas mask while dis- 



Figtjre 21. — Warehouse being fumigated with hydrocyanic acid gas by the pow- 

 der method. Calcium cyanide in dust form is spread on the floor, usually 

 from tin cans with perforated covers. 



tributing it. As in the case of the discoids, he should begin distrib- 

 uting the dust at the point farthest from the exit, so that he will be 

 working away from the gas that is being given off. 



After the fumigation, the paper on which the dust is spread can 

 be rolled up and thrown away, or the dust can be swept from the 

 floor and placed in containers, to be disposed of immediately. The 

 residue, which is mostly calcium hydroxide, is likely to absorb some 

 of the hydrocyanic acid from the air ; hence it is advisable to dispose 

 of it outside the building, where small quantities of escaping hydro- 

 cyanic acid gas will harm no one. After all the hydrocyanic acid 

 has been given off, the residue is nonpoisonous. 



i^s the dust may be blown about while the building is being ven- 

 tilated, it should be removed as soon as possible. To obviate this 

 difficulty, as well as for other reasons, the gas is sometimes liberated 

 in a special apparatus (fig. 38). Air is forced by a small motor into 

 a rubberized sack containing the calcium cyanide dust, which is kept 



