28 



BULLETIN 1313, U. S. DEPARTMENT OF AGRICULTURE 



Many of the fumigants and combinations of fumigants which 

 operated successfully in glass jars and in the presence of wheat in 

 bottles, boxes, and barrels gave disappointing results when used on a 

 large scale. A mixture, in equal proportions by weight, of ethylene 

 bromide and carbon tetrachloride, used at the rate of 16 pounds per 

 1,000 cubic feet, was successful when applied to weevils in wheat in a 

 box, but this mixture, even with the addition of 50 per cent more 

 carbon tetrachloride, was ineffective when used in box cars. This 

 is probably explained by the facts that in a box car the weevils may 

 be in the grain at a much greater depth than in a small box or barrel 

 and that the grain is much more tightly packed. Also, a box car is 

 not a tight container and the vapors of the fumigant may not be 

 long retained. 



The most successful fumigants used in the box-car tests were ethyl 

 formate in combination with carbon tetrachloride (12.1 pounds each 

 per 1,000 cubic feet) and ethyl acetate (12. 5 6 pounds per 1,000 cubic 

 feet) in combination with carbon tetrachloride- (25 pounds per 1,000 

 cubic feet). 



FIRE HAZARD FROM FUMIGANTS 



The vapor pressures of ethyl acetate and carbon tetrachloride are 

 very close for all temperatures up to their boiling points (Table 9, 

 Fig. l). 



Table 9.— Vapor pressures of ethyl acetate and carbon tetrachloride 



Temper- 

 ature 



Observed vapor 

 pressure 1 



Temper- 

 ature 



Observed vapor 

 pressure 1 



Ethyl 

 acetate 2 



Carbon 

 tetra- 

 chloride 3 



Ethyl 

 acetate 2 



Carbon 

 tetra- 

 chloride 3 



°C. 

 -20 



-10 







10 



20 



30 



mm. 

 6.55 

 12.95 

 24.30 

 42.70 

 72.80 

 118. 70 



mm. 

 9.92 

 18.81 

 33.08 

 55.65 

 89.55 

 139. 60 



°C. 

 40 

 50 

 60 

 70 

 80 



mm. 

 186. 20 

 282.20 

 415. 40 

 596. 30 

 832. 70 



mm. 

 210. 90 

 309.00 

 439.00 

 613. 80 

 * 836. 35 







1 Sydney Young. The vapor-pressures, specific volumes, heats of vaporization, and critical constants 

 of 30 pure substances. In Sci. Proc. Roy. Dublin Soc, n. s. (1909-10), / 2:374-443. 



2 Boiling point at 760 millimeters, 77.15° C. 



3 Boiling point at 760 millimeters, 76.75° C. 

 * Calculated. 



A mixture of 3 volumes of carbon tetrachloride and 2 volumes of 

 ethyl acetate (equivalent to 72.5 per cent carbon tetrachloride and 

 27.5 per cent ethyl acetate by weight) is noninnammable at ordinary 

 temperatures. Moreover, in this mixture the vapors of the two 

 components tend to separate but very slightly, thus making the 

 mixture safe from fire hazard. 



On the other hand, carbon disulphide has a much higher vapor 

 pressure than carbon tetrachloride at ordinary temperatures, thus 

 making mixtures of these compounds unsafe. The experiments of 

 the Underwriters Laboratories at Chicago (Grain Dealers Journal, 

 December 10, 1921, vol. 47, p. 798) show that a mixture of 75 per 

 cent carbon tetrachloride and 25 per cent carbon disulphide by vol- 



6 A mixture of ethyl acetate and carbon tetrachloride containing 33f per cent by weight of the acetate 

 will flash slightly at ordinary temperatures but will not continue to burn. 



