I. C. C. LARVICIDE 



385 



" A number of experiments were carried out for the purpose of obtaining a 

 cheap and efficient preparation for destroying mosquito larvae. Crude petroleum 

 oil was frequently too viscid to have a spreading power of the highest efficiency. 

 When mixed with crude carbolic acid, however, its spreading powers were in- 

 creased. From laboratory tests it was determined that crude petroleum for 

 surface use on pools should not be heavier than — ° Baume (American standard) . 



" Much of the crude carbolic acid supplied had been found upon analyses to 

 consist chiefly of inert neutral oils with a small proportion, 5 to 10 per cent, 

 of tar acids, and, as this crude acid was used extensively as a disinfectant, ex- 

 periments were conducted for the purpose of utilizing, if possible, this crude 

 carbolic acid as a disinfectant and larvacide. It was found that crude carbolic 

 acid, having a specific gravity not greater than 0.96 or 0.97, and containing 

 about 20 per cent of phenols or tar acids, when made into a soap, with common 

 resin and an alkali, yielded a product which was an ideal larvacide, having ex- 

 cellent diffusing and toxic powers, and at the same time was a very efficient 

 germacide. It diffused perfectly with water, forming a milky emulsion very 

 destructive to mosquito larva, and having a germicidal value of, or greater 

 than, that of pure carbolic acid of a Eideal-Walker coefficient of 1 to 2. In this 

 way a very valuable larvacide and disinfectant, miscible with water, was pro- 

 duced from a very inferior insoluble disinfectant. 



" The larvacidal powers, when tried with Culex and Anopheles larvae, varied 

 sKghtly with the quality of the crude carbolic acid, but an average result is as 

 follows : 



" Dilution 1 to 1000 : Culex larvae dead in five minutes 



Anopheles larvae, half grown, dead in five minutes. 

 Anopheles larvse, full grown, dead in ten minutes. 

 " Dilution 1 to 5000 : Anopheles larvae, half and full grown, dead in five 



minutes. 

 Culex larvae, half grown, dead in three minutes. 

 " Dilution 1 to 10,000 : Culex larvae, half grown, dead in sixty-four minutes. 



Anopheles larvas, young, dead in fifty-two minutes. 

 Anopheles larvae, full grown, dead in one hundred and 

 thirty-five minutes. 

 " Dilution 1 to 15,000 : Small Culex larvae, dead in thirty-two minutes. 



Anopheles larvae, full grown, dead in one hundred and 

 twenty-three minutes. 



" Anopheline larvae seem to be slightly more resistant than Culex larvae, and 

 all pupae are more resistant to the effects of the larvacide than larvae are." 



As the result of the experimental work with larvicides Colonel Gorgas and 

 his assistants have constructed a larvicide plant at Ancon, and in the monthly 

 report of the Department of Sanitation of the Isthmian Canal Commission for 

 August, 1909, it is stated that 14,G00 gallons of larvicide were made at a cost 

 of $0.1416 per gallon. The method of preparing this larvicide is quoted from 

 this report : 



" The method of making same is as follows : 150 gallons of carbolic acid is 

 heated in a tank to a temperature of 212° F. ; then 150 pounds of powdered or 

 finely broken resin is poured in. The mixture is kept at a temperature of 212° 

 F., 30 pounds of caustic soda is then added and solution kept at 212° F. until 

 a perfectly dark emulsion, without sediment, is obtained. The mixture is 

 thoroughly stirred from the time the resin is used until the end. 



" The resultant emulsion makes a very good disinfectant or larvacide. In 

 fact 1 part of it to 10,000 parts of water will kill anopheles larvae in less than 



