TOXICITY OF HYDROCYANIC ACID. 2QJ 



and it was not determined whether or not the insects close their 

 spiracles. However, when the methyl acetate was added to 

 liquid HCN, the average kill as shown from ten experiments 

 was 77.4 per cent, as compared with a 59 per cent, kill when 

 pure HCN was used. 



SUMMARY. 



A detailed study was made of the toxicity of HCN for certain 

 insects. The insects used in this work were two species of aphids, 

 Aphis rumicis and Macro siphoniella sanborni, one species of 

 thrips, Thrips (abaci, and two species of grain beetles, Sitophilus 

 granarius and S. oryza. Apparatus by which all factors can be 

 controlled or varied was employed. 



The results of over a thousand experiments indicate that, 

 within certain limits, concentration and length of exposure are 

 inversely related or that toxicity - - concentration X the time. 



The higher the temperature, the more susceptible were the 

 insects; this susceptibility was more pronounced with the 

 shorter exposures. 



Present indications are that humidity is not an important 

 factor affecting the toxicity of HCN. Comparative studies on 

 calcium cyanide and liquid cyanide show that the liquid HCN 

 is more toxic than the gases from hydrolysis of calcium cyanide. 

 A small amount of methyl acetate added to liquid HCN seemed 

 to increase the toxicity of the gas arising from the liquid HCN, 

 which may be due to the fact that a small amount of methyl 

 acetate kept the spiracles open, while in pure HCN the spiracles 

 were quickly closed. 



