18 



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



copper tubing three-eighths inch in diameter (fig. 17) is suitable. 

 Since it can be readily bent, elbow fittings are unnecessary, and com- 

 pression couplings can be used, except at the main inlet, where the 

 cylinders are connected. 



In large buildings, where there are several floors and numerous 

 branch lines must be used, each floor should be provided with a sepa- 

 rate riser, which should be of larger tubing. A spray nozzle (fig. 18) 

 should be provided for every 15,000 to 25,000 cubic feet of space. It is 

 customary to use from 10 to 18 nozzles to a riser, but the latter number 

 should not be exceeded. 



The piping system should be so arranged that the gas pressure will 

 be approximately the same at all nozzles, thus insuring an even distri- 





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Figure 15. — Fumigating a tobacco warehouse with hydrocyanic acid gas, using 

 the liquid method. The liquid hydrocyanic acid in the cylinder on the scales 

 is being forced, by air pressure generated by a small electrically driven com- 

 pressor, through the rubber tubing from the cylinder to the piping system in- 

 stalled inside but protruding through the walls. The operator shown should 

 be wearing a gas mask to protect against an accidental breaking of rubber 

 tubing or leakage from valves. 



bution. Each riser is connected to a special inlet pipe leading through 

 the outside wall of the building to the cylinders of gas. Piping plans 

 are usually made by the fumigating company after it has made a 

 survey of the building. Should blueprints or rough sketches and 

 measurements be forwarded for making piping plans, special attention 

 should be given to offsets and whole or part partitions. Any other 

 special conditions, such as heavily infested machinery, rows of packing 

 machines, or other places of heavy infestation, should be noted in 

 order that an extra nozzle may be added if it is thought desirable. 



APPLYING THE GAS 



Each cylinder of liquid hydrocyanic acid is supplied with an inlet 

 valve and an outlet valve. The outlet valve is attached to a steel tube 



