DUSTING COTTON FROM AIRPLANES. 
15 
a. m. The most favorable conditions for dusting are those existing 
from daybreak until very nearly the end of the dusting period, as 
the air is especially humid and hazy at that time, and the dust hangs 
among the plants well. As a general rule, in the daytime, the dust 
is whipped away from the nozzles of the dusting machine and blows 
off in the air without reaching the plant. 
The first series of flights were made during the day over Shirley 
cut Xo. 2. which immediately adjoined the landing field and offered 
a convenient opportunity for studying the behavior of the- dust in 
a fairly typical field. 
These first flights furnished an absolute surprise. It was found 
that when the calcium arsenate was dropped from the plane it was 
immediately broken up into a circular cloud which was quickly 
Fig. 13. — Dusting plane directly anproaching camera, showing trend of dust cloud. Note 
how this is blown both downward and to the left of the line of flight of the plane. 
blown down among the plants. This was obviously due to the tre- 
mendous rush of air past the plane and the additional blast created 
by the propeller, or. as it is commonly termed, the u slip stream." 
This combined air blast was so terrific that the powder encountering 
it became entirely subjected to its force and the effect of ordinary 
air conditions was very largely overcome. Throughout the experi- 
mental period flights were made at varying elevations, ranging from 
5 feet above the cotton plants to 50 feet above them, and it was almost 
always possible to distribute the poison from 25 feet or lower, regard- 
less of air conditions. It was sometimes possible to distribute the 
dust down among the cotton plants from even as high as 50 fett or 
more. Apparently the explanation of this fact lies in the air cur- 
rents set up by the plane and its propeller. 
Owing to the combined influence of the forward movement of the 
plane and the rotation of the propeller, the plane in flight is sur- 
