Distribution of HCN Gas in Greenhouse Fumigation 17 



over the ends of the tubes to prevent their escape. When the 

 desired atmosphere of HCN had been produced, the tubes con- 

 taining the aphids were dropped into the flasks quickly, and 

 placed in incubators and in the ice-box, so that the insects v^ere 

 subjected to various temperatures. 



There were four temperatures tried, 40°F. ; room tempera- 

 ture, or about 65 °F.; 80° F. and 100° F. Two periods of time 

 also were tried, 15 minutes and 30 minutes. 



CAPACITY 

 4,666 cu.fi. 



02. 4 6 e 10 la 14. lb le ao zz 24 26 t& ao 32 34 



Fig. 10. Graph of Fumigation No. 10 



A, left bench; B, middle bench; C, right bench; D, left col- 

 lecting tube; E, middle collecting tube; F, right collecting tube; 

 G, comb collecting tube. 



After the aphids had been removed from the flasks at the 

 end of the desired period of time, the flasks were connected to 

 an absorption apparatus similar to the one used in the green- 

 house experiments, and the HCN in the flask absorbed in the 

 same way, and titrated with o.ooiiV silver nitrate. In this way 

 an absolute check could be kept on the amount of HCN in the 

 atmosphere in the flasks. 



Using this method, it was found that as w^ould be expected, 

 the effectiveness of the fumigation was much increased by an 

 increase of temperature. The results of a number of tests for 

 minimum dosage are given in table 1. 



