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.) 



