174 The Control of Mosquitoes 



air or light, i.e., it must have good keeping 

 quality. 



7. It must be inexpensive. 



A number of commercial products now on the 

 market satisfy these conditions to a large extent. 

 Many of these have been tried and a few have 

 proved equal to some of the requirements. Others 

 were frauds. None ftilfilled all the requirements 

 desired. All commercial products were quoted 

 at high prices. The larvacide we finally adopted 

 cost one half less than commercial products. 



While working out the problem of a satisfactory 

 larvacide, Mr. Jacobs, the chemist of the Board of 

 Health laboratory in Panama, suggested the fol- 

 lowing formula for a larvacide : 



Resin, 150 to 200 pounds 



Soda, 30 pounds 



Carbolic acid, 150 gallons 



This product is a black liquid resin soap, that 

 freely emulsifies with fresh water. In brackish 

 or alkaline water emulsion does not take place. 



The active ingredient of the larvacide being 

 carbolic acid, to secvire uniformity in the larvacidal 

 power of the product it is necessary that the active 

 constituent of crude carbolic acid, phenol, shall be 

 tmiform in quantity. It is found that the best 



