2 BULLETIN 167, U. S. DEPARTMENT OF AGRICULTURE. 
benzene is harmful to human beings only in cases of internal applica- 
tion of large quantities, say from 30 to 40 grains. 
It is not advisable for sensitive persons to remain for a long time 
in a closed room where para-dichlorobenzene is freely exposed, as the 
odor may cause annoyance. On the other hand, para-dichloro- 
benzene can be used in closed or occasionally opened cupboards and 
even in sitting rooms without causing any inconvenience whatsoever. 
PARA-DICHLOROBENZENE AS AN INSECTICIDE. 
Experiments were conducted by the writer with para-dichloro- 
benzene to ascertain the practicability of its use and its insecticidal 
value against various insects. Para-dichlorobenzene as an insec- 
ticide is applicable to a large variety of insects, but under certain 
conditions depending on the variations in life history and environ- 
ment, and therefore necessitating specific methods of application. 
In a general way para-dichlorobenzene is effective only where its 
vapors can be closely confined, and when used in a higher tempera- 
ture than 74° F.; furthermore, it is recommended only where poison 
bait and contact sprays are either impractical or undesirable. The 
vapor is diffused through the air very rapidly and must, therefore, 
be closely confined in order to maintain a sufficient proportion in the 
air to prove fatal to insect life. 
The amount of material requged, under ordinary conditions, to 
bring about the desired effect is about 12. ounces of para-dichloro- 
benzene to every 100 cubic feet of space. The writer, however, 
suggests the use of a larger amount, 1 pound to 100 cubic feet, which 
will take effect more quickly and diminish the chances of revival, 
although revival is aberrent. At temperatures between 75° and 85° 
F. an exposure of at leagt 36 hours is necessary for best results. 
Temperatures above 85° F. require only 24 hours exposure, due to the 
fact that heat facilitates the diffusion of the vapors. 
Most warehouses and repositories contain several species of insects 
which possess very great tenacity of life, either in the adult or larval 
stages. In view of the fact that unless para-dichlorobenzene is used 
in enormous quantities or is permitted to remain in the respository 
over 48 hours, it does not injure plant life or render fruit, etc., inedible, 
we should, by preference, use as large a dose as possible for the com- 
plete eradication of the insects in the shortest possible time. As 
generally employed, the time would vary inversely to the amount of 
para-dichlorobenzene used. Since this substance is comparatively 
cheap and all unvolatilized material can be kept indefinitely, with 
very slight deterioration if the proper precautions are exercised, the 
additional amount of material required for a larger dose would be an 
insignificant item. Para-dichlorobenzene is insoluble in water and 
does not deliquesce when exposed to the air, but completely volatil- 
izes, and should therefore be kept in an air-tight can or glass jar. 
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