320 CONTROLLING INSECTS AND DISEASES 



A carburetor adjustable at a single point, the needle valve 

 controlling the gasoline flow, is desirable. When the point 

 where combustion is best has been located, it should be marked 

 and changes made only as the temperature varies or as the 

 engine through prolonged use varies in the internal relation- 

 ships of its parts. 



The oiling system should be thorough but simple, requiring 

 a minimum number of operations to care for it. 



Engines are mounted either in front or rear. On a team- 

 handled outfit, especially if the horses are uneasy, a front- 

 mounted engine is inconvenient to start. Turn the front 

 trucks at right angles so that the engine is more accessible. 

 On the other hand, the heavy load of material when the tank 

 is full moves more easily over the rear axle than over the front, 

 which should turn freely. In a few outfits engines are mounted 

 on top of the tank, but they are relatively inaccessible, in the 

 way of branches, and on the whole inconvenient. 



3. The Tank. Either wooden or steel tanks are used on 

 all standard makes of sprayers. The best Western cypress or 

 fir is not affected by corrosives used in spray mixtures, and 

 for many years they have been very satisfactory woods for 

 the manufacture of good spray tanks. Steel tanks are also 

 strong and tight. They may be made in almost any shape 

 and may be electrically welded and treated to give special 

 corrosion-resisting qualities. Wooden stave tanks of a 

 U-shape permit the withdrawal of all the material from the 

 corners. 



The tank may be mounted above the axles on bed pieces, 

 or underslung with the rear axle passing through the tank. 

 On hillsides, where it is important to have the center of 

 gravity as low as possible to reduce the danger of overturning, 

 the underslung tank, though more expensive, is preferable. 



Tank capacity will vary with the topography of the ground 

 and with the power available to haul the sprayer. The large 

 tank requires few trips to the filling points and is a time saver. 



