152 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



thpnnoinoters except on the first floor. However, realizing that it 

 required time to heat through heavy machinery and to penetrate 

 into several inches of flour, the heat was continued until (i a. m., by 

 which time it had penetrated the innermost recesses of the mill, save 

 the first floor. On the first floor the highest temperature was 105", 

 while one thermometer in four inches of wheat near the floor regis- 

 tered only 96°. (Chart VI.) On the second floor the highest tem- 

 perature, 133.5°, was registered by a thermometer hanging in the 

 open, while the lowest temperature, 117.6°, was registered by a ther- 

 mometer three inches in a sack of flour three feet above the floor. 

 (Chart VII.) On the third floor the thermometer in the open regis- 

 tered 141°, and the lowest temperature, 129°, was registered in a 

 flour conveyor spout four feet above the floor, ((^hart VIII.) On 

 the fourth floor the thermometer in the' open registered 128.6°, and 

 the lowest temperature, 118°, was registered by a thermometer in 

 flour in a conveyor six feet above the floor. (Chart IX.) 



The hydrograph was placed on the second floor in the middle of 

 the room. The relative humidity of this floor at 6 a. m., or just as 

 the heat was applied, was about 72 per cent. During the first few 

 hours there was a rapid decrease to less than 40 per cent, and during 

 the afternoon and through the entire night there was a very gradual 

 decrease to 12 per cent. 



After a very careful examination of the three upper floors, all parts 

 of the mill, even the deepest accumulations in the most inaccessible 

 parts, failed to show live insects, save in one corner on the upper 

 floor. In several places where there were accumulations inaccessible 

 to hydrocyanic acid gas, the conveyor or the bins were torn open, 

 and after being carefully inspected, did not reveal a live insect, but 

 showed that thousands had perished. In a sample room on the third 

 floor there were hundreds of samples of grain in paper and cloth bags, 

 tin cans, and sealed glass jars. These were badly infested; but all 

 of the insects were killed by the heat. On the fourth floor there was 

 a large flour conveyor running the entire length of the mill, and in this 

 conveyor the accumulation of flour which was from three to five 

 inches in depth was badly infested, but, after tearing it open from one 

 end almost to the other, it was found that all of the insects had per- 

 ished. Nearly three weeks later a second examination was made of 

 the mill and no live insects of any sort were found above the first story. 



In a mill, flour accumulates in recesses, and insects breed in places 

 inaccessible to the gas or vapor of any fumigating material, but heat 

 passes through all of these obstructions and penetrates the innermost 

 recesses. The writer has fumigated many mills with hydrocyanic 

 acid gas, but in no case has the fumigation proved so successful as 



