i66 The Control of Mosquitoes 



application to several times the initial value of the 

 oil. 



Heavy oils are best applied to water in the 

 form of a stream or spray. When applied in this 

 manner, the tendency to form a film is much 

 greater. A number of pumps on the market are 

 entirely satisfactory for this purpose. The pump 

 found most satisfactory in the Canal Zone was 

 called a "barrel pump" and was especially strong. 

 The smaller types of hand boiler-pumps are also 

 serviceable. The requisites of a good pump for 

 heavy oils are simplicity and strength of construc- 

 tion, and valves without rubber. 



It will be found occasionally that the heavier 

 fuel oils, those below 25° Baum6, are too thick for 

 the pumps ordinarily used. These oils may be 

 thinned by adding kerosene, two per cent, by 

 volume of crude carbolic acid, or five per cent, of 

 the "larvacide" described in this chapter. Other 

 compounds of a character similar to the "lar- 

 vacide" can also be used. 



A "knapsack sprayer" of the type used for 

 spraying in orchards has given satisfactory ser- 

 vice. This knapsack is made of heavy galvanized 

 steel, or of copper; it contains a small powerful 

 pump and has a capacity of five gallons. It 

 pumps very satisfactorily the asphaltum base 



