24 



CIRCULAR 6 3 5, U. S. DEPARTMENT OF AGRICULTURE 



cold, is satisfactory for attaching the cardboard and paper to the walls. 

 The doors can be sealed with gummed paper. For sliding doors it is 

 recommended that a mixture of 4 parts of asbestos and 1 part of cal- 

 cium chloride with water, worked into a stiff dough, be used. Cracks 

 in the walls, ceiling, and floors, sometimes caused by weather changes, 

 natural decay, or sinking of fundations, should be filled with the elastic 

 roofing cement (fig. 19). 



PIPING OF WAREHOUSES 



For best results from fumigation with hydrocyanic acid gas the 

 warehouse should be equipped with %-inch copper tubing and one 

 small spray nozzle installed for each 15,000 to 25.000 cubic feet. The 

 nozzles should be distributed about the building so as to provide the 

 proper dispersion of the gas. The piping system should be ar- 

 ranged so that the gas pressure is about the same on all nozzles. 

 Large tobacco warehouses containing several floors require branch 



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Figure 18. — Weekly catches of tobacco moths following periodic fumigations with hydro- 

 cyanic acid gas in tobacco warehouses having a total capacity of 3,318,000 cubic feet, 

 Richmond, Va., 1932. 



lines with separate risers. From 10 to 18 nozzles may be used to 

 a riser with satisfactory results. Detailed plans for piping ware- 

 houses can be obtained from the fumigating company after a survey 

 of the building and its contents has been made (fig. 20). 



When it is not advisable to pipe the warehouse to be fumigated, 

 a supply of rubber hose and nozzles can be obtained for use in 

 introducing the hydrocyanic acid. This hose for temporary use 

 can be rented from the fumigating company. 



APPLICATION OF HYDROCYANIC ACID 



Liquid hydrocyanic acid is shipped in steel cylinders equipped with 

 an inlet and an outlet valve. A small compressor is used to pump 

 air into the cylinder through the intake valve until a pressure of 

 about 100 pounds is obtained. Before connecting gas to piping, one 

 should be certain that all human beings and animals are out of the 

 warehouse. Read pages 39 and 40. The cylinder of hydrocyanic 

 acid is then joined to the piping system leading into the ware- 

 house, after which the outlet valve is opened. The pressure of about 



