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 3oth 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 



