INSECT CONTROL IN FLOUR MILLS. 31 



sively that the heat method, even at several degrees of temperature 

 higher than recommended for mill treatment, has no injurious effect 

 upon the baking qualities of the flour. A low hard-grade wheat 

 flour was subjected to a temperature of 140° F. for nine hours on 

 three successive occasions (the second and third heatings occurring 

 two and six weeks after the first heating), and a pancake flour was 

 subjected to a temperature of 130° F. for 48 hours without injurious 

 results. 



Effect of Heating upon Mill Humidity. 



Heating to kill mill insects greatly reduces the humidity in the 

 mill. Insects die more quickly in a dry heat than in a moist heat. 

 The relative humidity on the second floor of a mill at 10 a. m., when 

 the heat was turned on, was 93 per cent; by 12 m. it had fallen 

 to 40 per cent, and by 5.30 p. m. to 27 per cent. In a second mill 

 the relative humidity at 6 a. m., when the heat was turned on, was 

 recorded by a hygrograph as 72 per cent ; during the first few hours 

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

 during the afternoon and throughout the night there was a still 

 further decrease to 12 per cent. 



Important Points to be Considered in the Successful Heating of a Mill. 



1. Steam pipes should be located near floor and arranged to give 

 equal distribution of heat. 



2. Provide water trap for drawing off accumulation of water in 

 pipes. 



3. Lower floors and floors with heavy machinery should have more 

 radiating surface in proportion to cubic feet of space than upper 

 floors and floors with light machinery. 



4. Mill will heat more rapidly with a steam pressure of 25 to 50 

 pounds. 



5. To take advantage of heat in machinery begin heating mill 

 immediately after shutdown. 



6. Stairways and elevator shafts should be closed, so as to make 

 separate units of each floor. 



7. Thermometers should be placed at different points on each floor 

 that temperatures may be readily ascertained. 



8. Time must be taken to reach desired temperatures. 



9. A temperature of 118° F. to 125° F. is sufficient for any part of 

 mill. 



10. This temperature should be maintained for several hours to 

 allow heat to penetrate all infested parts. 



11. Do not attempt to heat on a windy, cold, or rainy day. 



