Aug. 13, 1917 



Volatility of Organic Compounds 



369 



gummy mass without completely evaporating. The toxicity of these 

 compounds, particularly piene and terpinol, is variable. Pinene usually 

 fails to kill the flies, while terpinol may kill with a certain dose one day, 

 while the following day the same dose is not fatal. Usually unless the 

 fli^s die in a short time after the introduction of the material, they will 

 survive the fumigation. These erratic results are no doubt due to the 

 oxidation of the terpene on exposure to the 

 air, thus producing a substance which is not 

 so toxic to the iiisect. Inasmuch as many 

 of the essential oils contain terpenes produc- 

 ing such gummy residues on exposure to the 

 air, it is at once apparent why varying results 

 have been reported as to their value as 

 insecticides. 



Table I and figures i, 2, and 3 show 

 that the toxicity of volatile organic com- 

 pounds is closely correlated with their 

 volatility. In general, the less volatile the 

 chemical the more toxic it is even where the 

 compounds are strikingly different in their 

 chemical composition. When related com- 

 pounds are considered, as in figures 4, 5, 6, 

 and 7, this agreement is even more marked. 

 Exceptions are noted, as in carbon bisulphid, 

 ethyl mercaptan, and particularly chlorpicrin. 

 These exceptions are not due to vapor 

 density, nor primarily to water solubility, but 

 are no doubt due to their chemical com- 

 position or to some peculiar action of the 

 chemical. Hydrocyanic acid, although not 

 included in this paper, would be an exception, 

 owing to its extreme solubility in water and the fact that such 

 minute quantities are sufficient to inhibit the action of oxidizing enzyms. 

 Chlorpicrin may be likewise an enzym poison. The remarkable point 

 of data here presented is not that there are a few exceptions, but the fact 

 that there are so few exceptions among so large a number of very different 

 chemicals which are strikingly different in their toxicological action on 

 higher animals. It is interesting to note that ethyl alcohol is more toxic 

 to insects than methyl alcohol, the reverse of that which takes place in 

 higher animals 



5! ^ 



I 



I 



Fig. 7. — Comparison of volatility and 

 toxicity of the hydrocarbons. 



