314 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



temperature, 48°C. to 52°C., could not he attained. Thi.s tempera- 

 ture kills all stage.s of the cereal pest's that I have tried in laboratory 

 experiments, excepting the young larva of Trogoderma ornatum, which 

 often requires 53°C. to 54°C. before succumbing to the effects of heat. 



In one flour mill all the return pipes from the heating system emptied 

 into open condensing tanks in the basement of the mill. The heating 

 of this mill was a partial failure, apparently due to the humid atmos- 

 phere and also to not being properly equipped with steam traps, or 

 condensers, so that a steam pressure of 40 to 60 'ipounds could be used 

 in the entire heating system. 



Soon after these failures to obtain the fatal temperature, experi- 

 ments were begun to substantiate or disprove this relative humidity 

 theory. A small water-jacketed oven was pressed into service; several 

 small hygrometers, some of which later proved to be inaccurate, and a 

 gas burner and some accurate thermometers completed the first set of 

 apparatus. A large series of tests using this oven, placing therein the 

 insects and material treated in small glass vessels with brass-cloth lids 

 to confine the insects, gave results which seemed to substantiate the 

 humidity theory. These results were not technically exact, hence 

 they need no further comment, excepting the fact, that they proved 

 chat moisture is a very important factor when using high temperatures 

 for the control of the insects affecting cereals and cereal products. 



The amount of heat required for a dry-atmosphere, high-tempera- 

 ture test was much less than for an extremely moist-atmosphere test, 

 demonstrating the necessity for more careful and exact experiments 

 along these lines, and proving in a rough way that the leaks in the heat- 

 ing system and wet floors were responsible for the partial failures 

 mentioned. 



Later, a small water-jacketed oven with an air-space surrounding 

 the water-jacket was procured and better grade hygrometers, besides 

 the wet and dry bulb thermometers, and an apparatus was devised for 

 circulating the air in the oven around the wet bulb thermometer. 

 Brass wire-cloth containers for the insects and material were also con- 

 structed in order to get more exact and uniform conditions throughout 

 the oven, and in the material treated. These small wire-cloth contain- 

 ers permitted the passage of the air through their walls and also the 

 rapid escape and ingress of moisture. It permitted the humid air in 

 the moist-atmosphere tests to come in direct contact with the insects 

 being treated, allowing very small chance for error. A series of ex- 

 periments were made, taking into consideration the previous experi- 

 ments and avoiding, as far as possible, the discrepancies which occurred 

 in the first series of tests. 



The inner walls of the incubator oven were covered with blotting 



