16 CIRCULAR 3 6 9, U. 8. DEPARTMENT OE AGRICULTURE 



and the operator must work with dispatch. The evolution of gas 

 can be delayed by wrapping the sack in paper and tying the bundle 

 with cord strong enough so that the bundle can be lifted and lowered 

 into the barrel without danger of breakage. A person can then lower 

 several charges before gas is discharged from the first. 



Placing the Generators 



In the fumigation of large open mills or warehouses, all the gener- 

 ators for one floor can be grouped in a position reasonably close to 

 the exit. It is not necessary to distribute them throughout the room, 

 for the gas is quickly dispersed to all parts of the enclosed space. In 

 fact, where it is impractical to seal off the several floors of a rather 

 small, tight building, excellent results can be obtained in calm weather 

 by placing all the generators on the lower floor so that the gas will 

 rise from floor to floor. 



How to Generate the Gas 



After the mill or warehouse has been prepared for the fumigation 

 and the generators have been placed in their proper positions, the 

 water and acid are measured out and distributed in the generators. 

 The acid can be poured from the carboys into heavy galvanized-iron 

 buckets, which will resist the action of the acid long enough for it to 

 be distributed without accident. If crocks are used for generators, 

 the acid must be poured into the water slowly with a rotating motion, 

 lest the heat developed by the chemical reaction between the acid and 

 water cause the crocks to break. If the crock should crack, the 

 operator must empty it immediately into some handy container pro- 

 vided for such an eventuality. 



When the water and acid have been mixed, the sodium cyanide, 

 which has previously been weighed into the proper quantities and 

 wrapped, should be lowered carefully into the generators. If several 

 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 exit (previously determined), proceed from generator to gener- 

 ator calmly and without delay. Do not retrace steps to a generator 

 accidentally overlooked. If several lines of generators converge at 

 one exit, an operator should be assigned to each line and at a prede- 

 termined signal each should start dropping the cyanide in the most 

 distant generator in his line. 



Since the gas is generated as soon as tha 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 1 or 2 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. 



