2g CIRCULAR 369, U. S. DEPT. OF AGRICULTURE 



is more quickly effective if it is first passed through a vaporizer and 

 introduced as a gas, as is the practice in vacuum fumigation. 



FUMIGATION WITH METHYL FORMATE-CARBON DIOXIDE 



MIXTURES 



Warehouses and storage rooms that are thoroughly modern in 

 construction can be fumigated with mixtures of methyl formate and 

 carbon dioxide. Ordinarily these mixtures are used only in special 

 fumigation vaults. The value of methyl formate as a fumigant was 

 first established by the experimental work of this Department. 

 Alone, its vapors are explosive and inflammable in the presence of 

 fire in any form; hence, mixtures with carbon dioxide have been 

 developed, the vapors of which are entirely free from the fire and 

 explosion hazard. 



The methyl formate-carbon dioxide mixtures are sold at from 10 to 

 35 cents per pound, depending upon the size of the cylinders and the 

 percentage of methyl formate used. They can be obtained in steel 

 pressure cylinders containing a net weight of 5, 8, 25, 50, or 60 

 pounds. When used in connection with vault fumigation, the cylin- 

 der is set on platform scales close to the vault wall, through which 

 the desired dosage is discharged. The method of application is the 

 same as that recommended for the methyl bromide-carbon dioxide 

 mixture. 



The vapors seem to be harmless to food and other commodities 

 thus far treated, and they are only slightly toxic to man as he ordi- 

 narily comes in contact with them in fumigation work. The recom- 

 mended dosage is 28 pounds per 1,000 cubic feet of empty space, with 

 an exposure of from 12 to 24 hours. Several mixtures have been 

 offered to the public, but one containing about 15 percent of the 

 methyl formate seems to be the most effective and safe. This fumi- 

 gating mixture is similar to the ethylene oxide-carbon dioxide mix- 

 ture in the manner in which it is marketed and used. 



VAULT FUMIGATION 



Many establishments have use for a small fumigation vault for the 

 treatment of incoming raw materials, returned goods, outgoing prod- 

 ucts, etc. Such a vault may be constructed of any material that can 

 be made gastight or reasonably so. 



Several types of metal vaults (fig. 27) can be purchased knocked 

 down ready for assembling. These are excellent in every way. 

 Highly satisfactory vaults can be constructed of concrete, brick, or 

 hollow tile, The brick (fig. 28) and hollow-tile (fig. 29) vaults 

 should be finished inside with a layer of Keen's cement and one or 

 two coats of paint. Wooden vaults with a metal lining are also • 



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 2-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 



