26 



FUMIGATION FOR THE CITRUS WHITE FLY. 



more than the actual requirement is ordinarily used, while it is gen- 

 erally considered that the use of three or four times as much water 

 as acid reduces the danger of shedding of the leaves from excessive 

 dosage. The experiments conducted by the writer relating to this 

 point have thus far given only negative results by failing to show 

 any relation between the proportion of the water and acid and the 

 effect of the gas upon the insects or the foliage. In 66 of the experi- 

 ments summarized hereafter a record was made of the proportion 

 of the water and acid. In nearly every case the object was to 

 determine the minimum dosage required, and while the record 

 included the proportions of the water and acid no effect of the varia- 

 tion in this regard was looked for until the results were summarized. 

 The chances, therefore, were ecpial in regard to the selection of a dose 

 of the required amount for greatest utility in the various tests. The 

 results in connection with the proportion of water and acid used 

 are given in the Table III : 



Tabi-e III. — Results obtained with varying proportions of irate r and arid. 



It will be observed from the table that the results seem to favor the 

 smaller amounts of water in proportion to the acid rather than the 

 larger amounts. The data are not extensive enough to establish this 

 conclusively, and it is not improbable that the difference in the 

 percentage of white flies killed has no conn.ection with the propor- 

 tion of water and acid. It is at least evident, however, that there 

 is no marked difference in favor of the use of water in a proportion 

 greater than necessary for the complete chemical reaction. The 

 Association of Horticultural Inspectors in 1903 adopted the formula 

 usually expressed 1-2-4, meaning 1 part of cyanid, 2 of acid, and 

 4 of water. Mr. Wilmon Newell's laboratory experiments « lead 

 him to conclude that this formula permits the volatilization of an 

 apparently maximum amount of prussic (hydrocyanic) acid. 



''B\il. IT), Georgia State Board of Entomology, i)p. 21-24, 1905.. 



