INSECTICIDES AND REPELLENTS 15 



emulsion in hard and even sea water and may be diluted with either 

 of them if soft water is not available. Xylene, however, has a low 

 flash point (about 80° F.); so its handling, transportation, and storage 

 present a fire hazard. A nonexplosive concentrate therefore has been 

 developed with solvents having a higher flash point (140°). This is 

 covered in a Federal specification (No. 8) issued in September and 

 October 1950. The published specification contains a list of 13 com- 

 mercial hydrocarbon solvents that have been approved by the Quarter- 

 master General. The concentrate is diluted 1 to 24 with water for a 

 mosquito larvicide or 1 to 4 for the standard 5-percent spray for 

 residual applications in buildings and for airplane spraying. 



A Federal lindane emulsifiable concentrate (No. 10) contains 20 

 percent of lindane, 7.5 percent of emulsifier, 40 percent (minimum) 

 of isophorone, and 32.5 percent (maximum) of alkylated naphthalenes. 

 A minimum flash point of 140° F. is specified for the alkylated naph- 

 thalenes and also for the concentrate. This concentrate is diluted 

 with water in ratios of 1:3 to give a 5-percent emulsion for airplane 

 spraying, 1:49 to give a 0.4-percent emulsion for outdoor ground 

 spraying, and 1:19 for a 1 -percent emulsion for residual spraying in 

 buildings. 



A chlordane emulsifiable concentrate (No. 7) calls for 46 percent 

 of technical chlordane in odorless kerosene. It is diluted in ratios of 

 1:22 to give a 2-percent emulsion for residual sprays in buildings and 

 1:45 for a 1-percent emulsion for outdoor work. 



The dieldrin emulsifiable concentrate (No. 9) contains 18 percent 

 of dieldrin in xylene and has a flash point of only 81° F. It is diluted 

 1:29 (0.6 percent of dieldrin) for outdoor ground spraying, 1:35 (0.5 

 percent) for residual treatments in buildings, and 1:59 (0.3 percent) 

 for use as a mosquito larvicide. It may also be diluted 1:5 in fuel oil 

 (3 percent of dieldrin) for airplane spraying. 



A commercial aldrin emulsifiable concentrate contains 41.7 percent 

 of the 60-percent aldrin-equivalent solution (see p. 10), which is equal 

 to 25 percent of aldrin. The solvent is specified as a petroleum hydro- 

 carbon having a minimum flash point of 115° F. The concentrate is 

 diluted 1:37 (about 0.6 percent of aldrin) for ground spraying and use 

 as a mosquito larvicide and 1:45 (about 0.5 percent) for outdoor 

 residual spraying. 



Wettable Powders 



A wettable, or dispersible, powder is prepared by grinding or blending 

 the insecticide with a readily wettable inert dust and adding a suitable 

 wetting or wetting-dispersing agent as necessary. 



Specifications have been prepared at the Orlando and Beltsville 

 laboratories for wettable powders containing 75 percent of DDT 

 (No. 30), 75 percent of lindane (No. 29), and 50 percent of dieldrin 

 (No. 28). Water is added to these materials to give suspensions con- 

 taining about the same concentrations of insecticide as for emulsions 

 (pp. 14-15), and they are used for much the same purposes. 



Several laboratories have attempted to develop colloidal or very 

 finely divided suspensions of DDT such as are obtained when a solu- 

 tion of DDT in a water-miscible solvent is added to water. Such 

 formulations remain in suspension much better than the ordinary 

 wettable powders, which require continuous agitation to prevent 



350828°— 55 3 



