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CIRCULAR 07 7. 1". S. DEPARTMENT OF AGRICULTURE 



gasoline burner before it is mixed with the insecticide and forced 

 through the nozzle, or the atomized solution is vaporized by a blast 

 of hot ah. Another model uses a small jet engine to produce a high- 

 velocity blast of heated air into which the insecticide is introduced 

 (fig. 12). 



The heated exhaust gas from motor vehicles has also been utilized 

 for the production of insecticide smoke (fig. 13). A venturi is in- 

 serted in the exhaust pipe, and the insecticide is introduced into this 

 constricted throat, where it becomes heated and then broken up by 

 the expansion of the gases after passing through the exhaust pipe. 



The droplets in such smokes or fogs are very small and remain air- 

 borne much longer than in most types of spray. For this reason the}' 

 are even more at the mercy of atmospheric conditions and may 

 therefore show much more variable results. In moderate breezes the 

 fog ma}' be carried long distances, and in rising air currents it will 

 rise immediately above the lower strata where the insects are resting; 



«■ - * 5 



Figure 10. — Portable Microsol machine. 



Figure 11. — Thermal fog generator mounted in a jeep. 



