commercial storage conditions. Sample operations were set up and performed 

 with the use of Navy material and equipment, 5 as shown in figure 4. Test appli- 

 cations which were exposed to weather conditions were examined 60 days later 

 and found to be intact and to have retained their sealing properties. After com- 

 pletion of the sealing on two groups of warehouses, inspections were made 4 

 months from the date of application and very little deterioration was noted in 

 excess of that shown in the earlier experiments. Industrial fumigation engineers 

 cooperated with the Department in making these tests and suggested methods of 

 application insofar as they applied to fumigation and use of HCN gas. 



Laboratory Tests 



One outstanding difference in the method of application used by the Navy and 

 that developed by the Department of Agriculture is the thickness of the material 

 when applied. Tests of plastic film made at the Richmond Laboratory of the 

 Bureau of Entomology and Plant Quarantine showed that the material effectively 

 prevented the transmission of hydrogen cyanide (HCN) at thicknesses above 

 0.005 of an inch. This finding made it possible to reduce gready the quantity of 

 material required and the cost of application as established by the Navy. 



PMA 1750 



p ; gure ^.—Experimental truck equipped by the Naval Ordnance Laboratory, Silver 

 Spring, Md., and used by the United States Department of Agriculture in experi- 

 mental work. 



Penetration of air under pressure on plastic 0.005 of an inch thick resulted in 

 the passage of 1 cubic centimeter of air per square foot in 24 hours. It was also 

 found that the material was not chemically affected by the exposure to hydrogen 



cyanide. 



Tests of Chemical Effect on Tobacco 



Further investigation revealed that the solvents used in the various types of 

 plastic materials tested were acetone and methyl ethyl ketone. To check the sus- 

 ceptibility and retentive qualities of tobacco to the vapors given off by the plastic 

 samples were exposed to the fumes under controlled conditions to a point beyond 



5 Material and equipment were obtained from the Atlantic Reserve Fleet at Norfolk Va., 

 with tie cooperation of the Navy Bureau of Ordnance and the Norfolk Naval Supply Depot. 



831768°— 49- 



