14 CIRCULAR 9 7 7, U. S. DEPARTMENT OF AGRICULTURE 



hand, light solvents are sometimes desirable for use with refined 

 kerosene for household sprays to permit rapid and complete evapora- 

 tion from materials on which the spray falls. The flash point should 

 also be considered, as materials with a low flash point may be danger- 

 ous under some conditions of storage or transportation. The boiling 

 points and flash points of DDT solvents are shown in table 1. 



Lindane and technical BHC are less soluble than DDT in most 

 of the organic solvents. However, this disadvantage is largely 

 offset by the fact that they are more toxic than DDT and may there- 

 fore be applied at lower concentrations. Fuel oil alone will dissolve 

 about 2.5 percent of lindane or 6 to 8 percent of BHC (40-percent 

 gamma content) in 1 or 2 days in warm weather, but 10 percent of an 

 auxiliary solvent such as xylene, isophorone, or Sovacide 544-0 

 will hasten the process and may be necessary to insure complete 

 solution in cool weather. Two quarts per acre of these solutions 

 will closely approximate the dosage of 0.1 pound of gamma per acre 

 recommended for mosquito control. With airplane spray units 

 designed to emit only 1 or 2 pints per acre it is necessary to use cor- 

 respondingly higher concentrations of lindane and BHC to give the 

 desired dosage. Preparation of such concentrations requires the 

 use of increased amounts of auxiliary solvents. 



Chlordane, being a liquid and miscible in all proportions with 

 petroleum oils, offers no difficulties in its formulation. For residual 

 sprays a 2-percent solution is usually employed. One military 

 specification (No. 22) covers two types of residual spray for roach 

 and ant control, one containing 2 percent of chlordane and the other 

 5 percent of DDT and 2 percent of chlordane. 



Dieldrin and aldrin solutions have not been covered in military 

 specifications, and for most purposes emulsions or suspensions are 

 preferable. In experiments on mosquito control, fuel oil solutions 

 containing 1.25 and 2.5 percent of dieldrin have been applied by 

 airplane to give dosages of 0.05 and 0.1 pound per acre. At these 

 concentrations an auxiliary solvent is not needed. 



Pyrethrum extract is issued as a 20-percent pyrethrins concentrate 

 in refined kerosene and can be diluted to the desired concentration 

 with the same solvent for space sprays. Allethrin is also readily 

 soluble in refined kerosene at the concentrations employed, usually 

 less than 0.5 percent. A space spray for indoor use containing 

 pyrethrins, piperonyl butoxide, and DDT is covered by a military 

 specification, and three space sprays — one containing pyrethrins, 

 synergist, and DDT; one with allethrin, synergist, and DDT (No. 

 26); and one with pyrethrins and synergist but without DDT — 

 are covered by Federal specifications. 



Emulsifiable Concentrates 



An emulsifiable concentrate is a concentrated solution of the insecti- 

 cide in an organic solvent to which an emulsifying agent has been 

 added. It is usually diluted with water to o-ive an emulsion. 



One of the first DDT emulsifiable concentrates developed at the 

 Orlando laboratory contained 25 percent of DDT, 65 percent of 

 xylene, and 10 percent of Triton X-100. It was used extensively by 

 both military and civilian workers as a mosquito larvicide and as a 

 residual treatment for mosquito and fly control. It forms a stable 



