FUMIGATION" OF CITRUS TREES. 
75 
result of the use of heavy dosages of fine fragments of cyanid is the 
burning and ultimate dropping of many of the leaves directly above 
the generator in the pathway of the rapidly rising gas. This result is 
usually spoken of as the "chimney" effect. The generator cover 
eliminates this " chimney" burning. 
A second and highly important point is the effect of open generators 
on the tent. The outer part, or skirt, as it is sometimes called, of 
fumigating tents is constantly being perforated with small holes, even 
when used by the most careful of workers. This effect has been 
noticed to some extent in the outfit of this investigation, which is 
believed to have been as carefully handled as any fumigation outfit 
could be. These holes are 
known to be acid burns. A 
few simple tests have demon- 
strated conclusively that 
many of these acid holes are 
due to acid carried along 
with the escaping gas and 
reaching that part of the tent 
nearest the generator. By 
placing large pieces of canvas 
in the path of gas escaping 
from open generators in 
which dosages similar to 
those often used in field work 
are employed it was found 
that drops of acid reached 
the canvas as high as 5 feet 
from the ground. The writer 
has frequently seen generat- 
ing vessels placed not more 
than 2 feet inside the tent. 
At such a distance one can 
readily see that drops of acid might reach the tent . The cover described 
above so deflects the gas, and incidentally such acid as is carried with 
it, that the drops are thrown to the ground, thus saving the tents. 
The decreased cost in mending of tents will doubtless pay for the cost 
of such a cover device several times over in a season of fumigation. 
A third advantage, which has not as yet been demonstrated, but 
which there is reason to believe will develop, is a better distribution 
of gas through the tent. Heretofore the most difficult part of the tree 
in which to destroy insects has been the lower part. This is also the 
part of the tree in which the purple scale is largely to be found. 
With the open generator the gas rises straight up in a narrow column 
for several feet, being broken up and distributed through the top of 
the tree first. As the gas is lighter than air, it is not to be expected 
Fig. 12.— A cover device attached to a fumigation generator. 
Corrugations in cover allow gas to escape. (Author's 
illustration.) 
