FORMALDEHYDE GAS NOT EFFECTIVE UPON FLIES. 



By E. S. Tucker. 



(Published by permission of the Chief of the Bureau of Entomology, U. S. Department 



of Agriculture.) 



DURING the disinfection of the contents of a room 12 by 14 

 feet, and having a height of 8 feet and 8 inches, for which 

 2 pounds of formalin and |- pound of permanganate of potash 

 crystals were used to produce formaldehyde gas, a number of 

 house flies were imprisoned. This treatment was put into action 

 at six p. M., on April 19, 1911, at Dallas, Texas, and the room was 

 kept tightly closed until the following morning. No effect upon 

 the flies could be detected after their confinement in the fumes 

 over night. To all appearances they were just as numerous and 

 active as they had been before the generation of the gas. Inspec- 

 tion failed to disclose a single dead fly, yet a strong odor of the 

 gas remained in the room on opening it for venti ation. 



Four hours of exposure to this gas, when it is produced accord- 

 ing to prescribed directions and in ratio with the space to be filled, 

 is considered an ample time for germicidal effect, if atmospheric 

 conditions are suitable. But in this case the gas was confined 

 fully 13 hours. The temperature of the air was moderate through- 

 out the night of the treatment, the minimum of 56° being regis- 

 tered early in the morning, and water had been sprinkled liberally 

 on the floor of the room to increase the humidity. These condi- 

 tions should have brought about perfect chemical action. Besides, 

 as may be noticed in the statement of amount of chemicals used, a 

 double quantity of formalin was poured on the requisite quantity 

 of permanganate of potash, the prescribed proportions being 10 

 ounces of the former to 5 ounces of the latter per 1000 cubic feet 

 of space with suitable atmospheric conditions. 



The test affords definite proof that formaldehyde gas, even in 

 nearly double disinfectant strength, is useless as an insecticide, at 

 least against flies. It is in fact only claimed to be effective upon 

 insects when they are confined in concentrated gas for some time. 



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