INDUSTRIAL FUMIGATION AGAINST LN SECTS 



31 



popular. It is possible to purchase 14-gage sheet metal cut up into 

 sections for constructing a vault 8 by 10 by 12 feet. When welded 

 together, the sections form an excellent gastight lining. 



The cheapest type of vault is made of wood. A useful vault can 

 be constructed of two layers of 1-inch standard flooring separated by 

 a layer of heavy roofing paper. If the edges of each board are 

 painted with heavy white lead paint just before the tongue and 

 groove are forced tightly together, the walls are even tighter. The 

 floor, walls, and roof should be of the same tight construction. The 

 interior should be given two or three coats of any good paint. An 

 aluminum paint is sometimes used to advantage. 



Figure 26. — Outdoor structure built for fumigation of dried fruits. It is made 

 of hollow tile, plastered on the inside with Keen's cement, and equipped with 

 a refrigerator-type door. Note funnel-shaped openings above the door, through 

 which a liquid fumigant can be poured into evaporating trays suspended from 

 the ceiling of the vault. (Photograph by Perez Simmons.) 



All types of vaults should be equipped with a refrigerator or safe 

 type of door, well gasketed to make it gastight. 



A ventilating system capable bf quickly removing the fumigant 

 from the vault after the fumigation is essential. If the vault is set 

 up inside a building, the ventilating stack must extend outside the 

 building and preferably above the roof. 



It is sometimes desirable to install an electrical heating unit, con- 

 trolled by a thermostat, so that a constant high temperature can be 

 maintained throughout the fumigation. The heating unit should not 

 be operated, however, while inflammable fumigants are being used. 



For applying the fumigant several different methods can be used. 

 For heavier-than-air gases a shallow evaporating pan or trough 

 should be installed near the ceiling of the vault, with a feed pipe ex- 

 tending outside (fig. 26). The fumigant can then be run into the 

 evaporating pan by gravity or compressed air. If liquid hydro- 

 cyanic acid or any of the commercial mixtures is to be used, a short 



