INDUSTRIAL FUMIGATION AGAINST INSECTS 17 



eral floors are to be fumigated separately, the cyanide should be 

 dropped first into the generators on the top floor, and then on the 

 next lower floor, and so on to the bottom. Starting with the one 

 farthest from the exist (previously determined), proceed from gen- 

 erator to generator calmly and without delay. Do not retrace steps 

 to a generator accidentally overlooked, as you might encounter 

 higher concentrations of gas than your canister could protect 

 you against. 



If several lines of generators converge at one exit, an operator 

 should be assigned to each line and at a predetermined signal each 

 should start dropping the cyanide in the most distant generator in 

 his line. 



Since the gas is generated as soon as the acid- water mixture comes 

 in contact with the sodium cyanide, the operators engaged in drop- 

 ping the cyanide should wear gas masks, except for very small jobs 

 where only one or two generators are used. 



Emptying the Generators 



When the fumigation is finished and the building has been thor- 

 oughly ventilated, the residue must be emptied from the generators. 

 Sometimes the chemical reaction is incomplete because some of the 

 sodium cyanide has not come in contact with the acid-water mixture 

 or because the wrong proportions of the materials have been used. 

 Therefore, when the generator is moved, the contents are shaken up 

 and additional small quantities of gas may be given off. For this 

 reason the operator should always wear a gas mask while handling 

 the barrels and should not hold his head over the barrel. 



The residue, which is poisonous, can be disposed of by dumping it 

 down a street drain or by pouring it into a hole in the ground and cover- 

 ing it with soil. 



THE LIQUID METHOD 



Liquid hydrocyanic acid is a volatile, colorless liquid, which boils at 

 79° F. It is marketed in cylinders containing 30 or 75 pounds. On 

 exposure to air it gives off the same gas that is generated by mixing 

 sodium cyanide with sulfuric acid and water. In the hands of an expert 

 fumigator it is an almost ideal fumigant for use in large enclosures. 



After a building has been prepared for fumigation, the gas is ap- 

 plied entirely from the outside (figs. 15 and 16). The cylinders con- 

 taining the liquid hydrocyanic acid are lined up near the building, 

 and the fumigant is forced in by compressed air. A proper distribu- 

 tion of the gas within the building is obtained by means of lines of 

 pressure rubber tubing or metal piping equipped with spray nozzles. 

 A gas mask should be worn at all times by the operator introducing 

 the gas. 



PIPING THE BUILDING 



In small enclosures the gas can be distributed through rubber tub- 

 ing, but in large warehouses or mills it is desirable to install a perma- 

 nent system of piping. This may be constructed of iron, brass, or 

 copper. The iron piping is the least expensive, but, owing to its 

 tendency to rust and cause clogging of the spray nozzles, it is rarely 

 used. Either brass or copper tubing is recommended. A flexible 



464673°— 42 -3 



