2O6 F. J. BRIXLEY AND R. H. BAKER. 



HUMIDITY. 



Several humidity experiments were conducted using Aphis 

 rumicis, Sitophilus granarius and S. oryza under various relative 

 humidities, other factors being the same. The result of these 

 experiments indicate that humidity is not an important factor in 

 determining the toxicity of HCN. 



COMPARISON OF THE TOXICITY OF LIQUID HCN AND CA(CN) 2 . 



During the course of the experiment, the question arose as 

 to the comparative toxicity of hydrocyanic acid resulting from the 

 action of water vapor on Ca(CN) 2 and the HCN volatilizing 

 from liquid HCN. It is known that in addition to HCN, 

 there are other compounds, such as ammonia and hydrogen 

 sulphide, which arise from hydrolysis of Ca(CN)2, and so it was 

 thought advisable to ascertain what effect these foreign gases 

 would have upon the toxicity of HCN. 



The results indicate that the pure HCN coming from liquid 

 HCN is slightly more toxic than the gas mixture which arises 

 from Ca(CN)2. These results are also confirmed in a number of 

 experiments by adding slight quantities of NH 3 and H 2 S to the 

 gas which arises from liquid HCN, showing that there is some 

 antagonistic action between the ammonia, hydrogen sulphide 

 and HCN, thus lowering the toxicity of HCN. 



EFFECT OF METHYL ACETATE ON THE TOXICITY OF HCN. 



Some insects, such as Melanoplus differentialis, when placed 

 in a sublethal concentration of HCN, close their spiracles and 

 thus prevent, to a certain extent, the entrance of the cyanide 

 gas. 



It was thought that if some chemical could be mixed with 

 the HCN, which would keep the spiracles open, the insects would 

 be more easily killed by cyanide than if the spiracles are allowed 

 to close. Methyl acetate is found to keep the spiracles open in 

 M. differentialis when the insect is placed in an atmosphere of 

 HCN. Experiments were conducted to determine what effect 

 the addition of a small amount of methyl acetate would have 

 upon the toxicity of pure HCN. The only insects available at 

 the time of the experiments were 6 1 . granarius (grain beetle), 



