SOME FACTORS AFFECTING THE TOXICITY OF 

 HYDROCYANIC ACID FOR INSECTS. 



F. J. BRINLEY AND R. H. BAKER,' 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF PENNSYLVANIA. 



During the last twenty years a vast amount of work has been 

 done on the control of injurious insects by the use of hydrocyanic 

 acid. Inasmuch as little quantitative work seems to have been 

 done on the influence of environmental factors, such as tempera- 

 ture and humidity, upon the toxicity of HCN to insects, and 

 since the relation of concentration of cyanide to length of exposure 

 also does not seem to have been thoroughly investigated, it was 

 thought advisable to study these points in some detail. 



APPARATUS AND METHOD. 



To determine the effect of concentration of cyanide, length of 

 exposure, temperature and humidity upon the toxicity of HCN 

 to insects, apparatus by which all these factors can be controlled 

 or varied must be employed. In the present experiments, such 

 apparatus was devised and proved to be very satisfactory. 2 



The apparatus, as shown in Fig. I, consists of the following 

 units: (^4) flow regulator (one-inch glass tube 5 feet long); 

 (B) humidifying unit, consisting of two half-liter bottles; (C) 

 two flow meters; (D) generating flask; (E) half-liter bottle 

 used as a fumigation chamber, placed in a water bath; (F) a 

 small absorption bottle used for collecting samples of gas for 

 analysis; (G) a one-liter bottle filled with NaOH for absorbing 

 the gas. The outlet at H is attached to a suction pump. 



The air flows in the direction indicated by the arrow. The 

 rate of flow can be regulated by raising or lowering the glass tube 



1 This work was done in cooperation with the American Cyanamid Sales 

 Company. 



2 The writers wish to acknowledge the assistance given by Mr. K. D. Ashley, 

 of the Chemical Staff of the American Cyanamid Sales Company, who furnished 

 valuable suggestions for devising the apparatus and for the colloidal silver iodide 

 method of analysis. 



2OI 



