162 MOSQUITO ERADICATION 



tank. The product is ready in a few minutes, yielding about 3}i 

 barrels. As a mosquito larvicide, it is used by spraying an aqueous 

 emulsion (1 part of larvicide to 5 of water) over the surface to be treated 

 and along the margins of pools and ponds or other mosquito-breeding 

 places, so that the resultant dilution of the larvicide has a thin, milky 

 opalescence, representing approximately a dilution of 1 to 5,000. A 

 1 to 1,000 dilution kills the larvae more rapidly, and was used for destruc- 

 tion of larvae in overflowing pools, etc., and where the use of oil was 

 not practicable." 



This mixture, LePrince reports, in addition to being a good 

 larvicide and a good disinfectant, also proved to be very useful in 

 destroying algae. He also found it very useful for thinning 

 down heavy oil. 



OTHER LARVICIDAL SUBSTANCES 



Niter cake is a by-product of the manufacture of fertilizer, the 

 active principle of it being free sulphuric acid. It has been used 

 successfully for fire-barrels, 3 or 4 pounds of it being dropped 

 into each barrel. It has not proven altogether satisfactory for 

 pools, catch-basins, etc., as, it is believed, the alkalinity of the 

 soil often neutralizes much of the acid. As niter cake, where it is 

 available at all, can generally be obtained gratis, it may be 

 used profitably in artificial containers, provided its poisonous 

 properties do not make it objectionable. 



Creosote has been used successfully on a small scale, parallel 

 with the Panama, mixture, as a substitute for oil. It is, of 

 course, open to the same objections regarding its poisonous 

 properties as the Panama mixture. It is said to be particularly 

 useful in protecting the edges of ponds and streams and in places 

 where heavy verdure interferes with oil spraying. Fish in a 

 flowing stream or in a large body of water are not injured by 

 spraying the margins with creosote, it is reported. 



Water gas tar, a by-product of the manufacture of gas, con- 

 taining phenol, creosote and other larvicidal substances, has also 

 been reported as a satisfactory substitute for oil. It is applied 

 similarly to oil. It is said to make a very effective mixture with 

 kerosene or with kerosene and fuel oil. The proportions recom- 

 mended by Bishop 1 are: 1 gallon tar to 5 gallons kerosene, and 1 

 gallon tar to 2 gallons fuel oil and 5 gallons kerosene. He states 



1 Transactions of the First Annual Conference of Sanitary Engineers, 

 U. S. Public Health Service, 1919. 



