44 



FUMIGATION FOR THE CITRUS WHITE FLY. 



Table VI. — Data concerning dosage in those experiments in ivhich 100 per cent of vhite 



Jties were destroyed. 



These tables show that with tents of 8-ounce duck and untreated 

 with paint or sizing there is Httle or no advantage in exposures of 

 more than 40 minutes. The results with exposures of 30 and 40 

 minutes compare favorably with those ranging from 45 minutes to 

 2 hours and 50 minutes. It is evident that the gas escapes rapidly 

 and that in the course of a period of 80 to 40 minutes at the most 

 the gas from a dosage of maximum utility is so diluted as to be 

 practically ineffective. On the other hand, the table shows con- 

 clusively that the experiments afford no justification for reducing the 

 dosage on account of lengthening the exposure from 45 to 60 minutes 

 or longer. Everything considered, the writer adopted the 40-minute 

 period of exposure as probably affording the greatest benefit from a 

 given amount of cyanid. 



As an aid in determining the rates of dosage which could be safely 

 recommended for the various ratios of leakage surface to cubic con- 

 tents, the experiments referred to in Table V were arranged in accord- 

 ance with the ratio, and in each case the writer estimated the amount 

 of potassium cyanid which it seemed evident would have been amj^le 

 for the destruction of all the insects. The degree of success obtained 

 with the amount of potassium cyanid actually used was taken into 

 consideration in estimating the amount needed. The data thus 

 arranged, together with calculations of the rate, or number of cubic 

 feet of space per ounce of potassium cyanid, are given in Table VII. 



