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 fully realized by entomologists and 
orchardists there is no doubt that better and more satisfactory 
results will be obtained. 
&t 
