12 MISC. PUBLICATION 4 84, U. S. DEPT. OF AGRICULTURE 



like the cart machine, but has a gasoline motor on the platform to 

 furnish the power. Another kind of power duster is bolted on the 

 rear of a tractor and is operated from the power take-off of the tractor. 

 The power-operated dusting machines are best suited for large farms, 

 with 100 to 300 acres of cotton. 



Since about 1922 the airplane, too, has come to be used as a dusting 

 machine (fig. 9). Of course this does not mean that any airplane can 

 be used for this work. The low flying that is done in cotton dusting 

 is more dangerous than that done high up in the air. The plane has 

 to be flown so close to the ground that it almost touches the cotton 

 plants, and it cannot be flown so fast as those high up in the air. 



S 



Figure 9. — Calcium arsenate dust being applied to a field of cotton by airplane. 



Fortunately for this kind of work there are specially built planes 

 that can stay in the air while going much more slowly than ordinary 

 planes. 



The dusting planes must also have special machinery for carrying 

 and releasing the poison dust. There is a little door to the dust 

 compartment that can be opened when the airplane pilot is ready for 

 dusting work. This opening can be so regulated as to let out just the 

 quantity of calcium arsenate needed and then closed when no more is 

 necessary. When the door is opened, a stream of dust falls through 

 and is violently driven backward and downward by the current of 

 air from the airplane propeller. Gradually the dust cloud spreads 

 outward to each side of the plane and drifts in very fine particles to all 

 parts of the cotton plants (fig. 9). One airplane will dust as much 

 cotton as 50 cart dusters. 



Airplanes for cotton dusting are not owned by individual planters, 

 as is the usual dusting machinery, for they are far too expensive for 

 most farmers to own. Instead, they are owned by commercial com- 

 panies that do the work for the planter at a definite price per acre. 



