MILLS AND OTHER BUILDINGS 157 
This experiment was thoroughly satisfactory, and 
being the first of the kind ever tried in a mill, so far 
as known, was of special importance. Where only a 
single floor is fumigated, we would naturally expect 
some insects in the floor and beneath it to escape, as 
the gas is lighter than air and rises. A room, there- 
fore, would have to be perfectly tight, and enough 
gas generated to fill it before the fumes would reach 
the floor and penetrate the cracks and crevices. It 
would be only a few moments after fumigation before 
insects would again come through the cracks in the 
floor from the basement below and perhaps the floor 
above. 
To be successful in the greatest degree the mill 
should be thoroughly filled at one time with the gas. 
For instance, if only a single room or floor is used and 
the gas is generated, the insects become very uneasy 
when they begin to feel uncomfortable, and run here 
and there in search of a crack through which to 
escape; but if every room is full of gas there is no 
possible means of escape, except through some crack 
leading outdoors. 
Second experiment in mills—In an Ohio mill, 
June 20, 1899, we tried another experiment on one 
floor only, using ten pounds of cyanide at the rate of 
0.12 gramme per cubic foot of air space. The 
chemicals were placed, according to my directions, in 
the hands of an expert chemist. June 30th the owner 
sent a sample of web and material from the room, and 
wrote me as follows: ‘‘I send you by mail, under 
separate cover, a sample of moth, weevil, and bugs the 
gas destroyed. I wish to thank you for what you 
