OILING METHODS 



Kinds of Oil. — Oil forms a perfect film over the 

 surface of the water, which prevents the mosquito 

 larvae and pupae from breathing and thus results in 

 suffocation. The most desirable oil for the purpose 

 is one that will spread most readily without breaking 

 up into patches and that will remain on the water in 

 an effective condition. Crude oil breaks up in patches 

 between which the water is not affected, so that the 

 wrigglers have been found by the writer developing 

 in such places where this oil has been liberally used. 

 Crude oil, furthermore, cannot be used as such in ordi- 

 nary spray pumps. Therefore this material is not to 

 be recommended in this form for mosquito control. 

 Its lasting qualities are very good, however. Kero- 

 sene spreads most satisfactorily and does its work 

 quickly, but evaporates in a comparatively short 

 time, thus requiring frequent repetition. A combina- 

 tion can very well be made of the two which will 

 bring about more nearly the desired results. Our 

 best results have been obtained with a mixture of equal 

 parts of crude oil and kerosene, though the proportion 

 may perhaps safely range to three parts of the former 

 to one of the latter. We have also used successfully 

 a treated stove oil of about 3 2° Beaume gravity. 



Oil purchased on the market as "crude oil" varies 



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