100 



narrow line of coal-tar along an especially prepared path at the edge 

 of the field, with post-holes dug at intervals beside the line to trap and 

 hold the bugs. This method, tho long in use. has certain serious handi- 

 caps, owing especially to the nature of the material used in making the 

 impassable line ; and I undertook to find some substance better suited 

 to the purpose. Coal-tar answers admirably when first poured out. 

 its adhesiveness and offensiveness preventing the passage of the bugs, 

 which ordinarily do not even attempt to cross the line, and are imme- 

 diately destroyed if they touch it. It is. however, so fluid at tempera- 

 tures high enough to stimulate the chinch-bugs to escape from barren 

 stubble fields that it sinks too quickly into the ground and must be 

 cften renewed at a large cost of labor and material. Even before it 

 has thus disappeared, exposure to the air causes a film to form upon 

 its surface so that it may be crossed by the bugs readily and without 

 injury. Moreover, as it is a by-product of gas manufacture, its supply 

 is limited and can not be increased to meet an increasing demand ; and 

 its price, already high for the purpose, is certain to rise when the de- 

 mand becomes unusual. 



Experiments with Coal-tar Mixtures and Petroleum Products 



Beginning in late August. 1910. an elaborate series of tests were 

 made at Urbana of mixtures of coal-tar with various denser or pow- 

 dered substances such as might give it greater body and so prevent its 

 sinking too rapidly into the hot earth. Other experiments were made 

 by mixing with it less volatile oils, resins, etc.. which, uniting with 

 coal-tar. in solution, might make the mixture more lasting when ex- 

 posed to the heat. These various substances were tested in an electric- 

 oven the heat of which could be controlled, and in the open air out-of- 

 doors. One hundred and thirty-five experiments of this character 

 were run thru in the month of September with the result that a few of 

 the substances tested seemed worthy of trial in the air under condi- 

 tions as nearly like those of an Illinois summer as could be found at 

 that late season. For this purpose Mr. Flint was sent to Brownsville. 

 Texas, at the mouth of the Rio Grande River, with instructions to imi- 

 tate on a small scale our standard field operations against the chinch- 

 bug at harvest-time. The temperature, even thus far south, was. how- 

 ever, at the time of his visit (November 19 to December 3).. too low to 

 afford a fair test. The minimum readings in the open air ranged from 

 43 to 72 degrees in the shade and the maximum from 68 to 86 degrees, 

 with a maximum temperature of 109 degrees P., at the surface of the 

 soil in the sun. The substances whose efficiency was compared with 

 respect to the time during which they would continue sticky enough 

 to keep chinch-bugs from crossing them were coal-tar. 18-gravity oil. 

 Heppe's flux oil. asphalt oil. and Superior oils Xos. 1 and 2. Of these, 

 Heppe's flux oil, a petroleum product, proved to be from five to 

 seven times as lasting as coal tar. As an average of eleven identical 



