INSECTICIDES, FUNGICIDES, AND SPRAYING 211 



will be found equally satisfactory for spraying shade-trees 

 when only a limited number are to be treated. 



Power-Sprayers. — For spraying very large trees and for 

 city work in general, power sprayers are absolutely neces- 

 sary. There are many kinds of spray outfits of which those 

 run by gasoline and by liquid carbon dioxid are now the 

 most common in use. Gasoline sprayers consist of a gaso- 

 line motor, pump, and insecticide tank. The transmission 

 of power from the motor to the pump is either by means of 

 a belt, or the pump and engine are directly connected by 

 reduction gearing. The latter arrangement is much the 

 better. The insecticide tanks are usually of about two 

 hundred gallons capacity. 



A very necessary accessory of the insecticide tank is an 

 agitator to stir the spraying mixture while the machine is in 

 operation. This may be either a mechanical contrivance 

 operated by the engine or of the jet type. The latter con- 

 sists of a jet of the spraying mixture sent back into the 

 tank by the pump. If the capacity of the motor is ample, an 

 agitator' of the jet type is excellent; but if the pressure is 

 very much reduced by sending some of the liquid back to 

 the tank, a mechanical agitator is to be preferred. 



Whether the agitator be of the jet or the mechanical type, 

 it is very important that it should be worked by the engine 

 and not by man power. When a man is put to turning a 

 crank for eight or ten hours a day, the chances are that the 

 agitator will not work very uniformly. As a result, when 

 such mixtures as arsenate of lead are used, the precipitate 

 will settle and the spraying will be done with clear water. 

 The writer has known of many cases of ineffective spraying 

 work due to inefficient agitating devices. 



The sprayers operated by liquid carbon dioxid have 



