CEREAL PESTS INSECTS 501 



6 A.M. the following day by the regular method of steam 

 heating employed in the mill, but a water trap was at- 

 tached to draw off the accumulated water in the steam 

 pipes, and the steam was turned on directly with pressure, 

 so as to heat the mill more rapidly. Four thermometers 

 were placed on each of the 4 floors, both in the open and 

 in the different depths of flour or other accumulations. 

 At the beginning the average mill temperature was 90, 

 and that outside 77. At 3 P.M. fatal temperatures were 

 reached in several parts of the mill, and at 6 P.M. many 

 insects had perished. At 9 P.M. fatal temperatures were 

 shown by nearly all the thermometers except those on 

 the first floor. By 6 A.M. the next day the heat had 

 penetrated the innermost recesses of the mill, except on 

 the first floor. 



At the end of this demonstration there were no live 

 insects on the 3 upper floors, even in the deepest ac- 

 cumulations and the most inaccessible parts, save in one 

 corner of the fourth floor. In several places inaccessible 

 to any gas the conveyor and bins were torn open, and not 

 one live insect was seen, but thousands were found dead. 

 Insects infesting samples in tin cans and sealed glass 

 jars in a sample room, and inaccessible to gas, were all 

 killed. Three weeks later a second examination of the 

 mill revealed no live insects of any kind above the first 

 floor. 



547. The advantages of the heating method are 

 several: (1) insects breed in places inaccessible to gas or 

 vapor, but heat passes through all obstructions to the 

 innermost recesses. (2) Many insects do not yield 

 readily to hydrocyanic acid gas, but no stored grain or 

 flour insect can withstand a temperature of 118 to 122, 

 for any length of time. (3) Fumigation with hydrocyanic 



