INSECTICIDES AND REPELLENTS 17 



and W. N. Sullivan of the former Bureau of Entomology and Plant 

 Quarantine and later developed in cooperation with the Army and 

 Navy for greater economy in the use of pyre thrum. The insecticide 

 was dissolved in liquefied Freon-12 (dichlorodifluorome thane) and 

 confined in refillable seamless steel cylinders, or "bombs," which have 

 a capacity of 1 pound. When the liquefied gas containing the insecti- 

 cide was released through its own pressure (82 pounds per square 

 inch at 68° F.), the insecticide was dispersed in the air in very fine 

 particles, providing an effective and convenient method of destroying 

 mosquitoes in tents, barracks, billets, bomb shelters, and other con- 

 fined spaces. Later DDT was added to the formula. The specifica- 

 tion issued in January 1950 (No. 1) contains 0.4 percent of pyrethrins, 

 3 percent of DDT, cyclohexanone and hydrocarbon oil 5.0 to 5.5 

 percent each, and Ireon-12 to make 100 percent. 



After World War II it was found that a 50-50 mixture of Freon- 

 1 1 (trichloromonofluorome thane) and Freon-12 provided a satisfactory 

 aerosol propellent having a pressure of less than 55 pounds per square 

 inch at 70° F., which permitted the use of a low-cost tinplate con- 

 tainer (fig. 1). Two types of low-pressure aerosols in 12-ounce con- 

 tainers have been used by the Armed Forces, one containing 0.6 

 percent of allethrin (No. 2) and the other 0.4 percent of pyrethrins 

 (2 percent of a 20-percent extract) plus 1 percent of piperonyl bu- 

 toxide. Both types contain 2 percent of DDT, 5 percent of alky- 

 lated naphthalenes, 5 to 7.4 percent of deodorized kerosene, and 41.2 

 to 42.5 percent each of Freon-11 and Freon-12. A valve delivery 

 rate of 0.65 to 1.25 grams per second at 80° is specified. 



Figure 1. — A low-pressure aerosol dispenser. 



