CHEMISTRY OF FUMIGATION. 105 



the amount of hydrocyanic-acid gas that can be used falls within 

 narrow limits. If the application is too strong serious injury will 

 result to the trees, while on the other hand if too weak many of the 

 insects will escape the poisonous action of the gas, thus necessitating 

 a second fumigation or giving inefficient results. It is therefore 

 necessary that the strength and quality of the reagents used be 

 known and that the conditions under which the work is done be 

 uniform. When these points are full}' realized by entomologists and 

 orchardists there is no doubt that better and more satisfactory 

 results will be obtained. 



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