101 



tests, with temperatures ranging during each trial from 40 to 109 de- 

 grees, a narrow line of this oil poured upon the leveled earth of a back- 

 furrow remained sufficiently sticky, without renewal, for twenty-one 

 hours; and poured on inverted sod it continued effective in tempera- 

 tures ranging from 40 to 103 degrees for thirty-eight and a half hours, 

 as an average of six tests. On the other hand, nineteen tests with coal- 

 tar applied to a back furrow gave an average of four hours and ten 

 minutes with temperatures ranging from 40 to 100 degrees ; and seven 

 experiments with its application to sod gave an average duration of 

 five hours. 



Tlie Petroleum Road Oils. — My attention being thus called to the 

 possibility that petroleum residues might be found a more efficient and 

 dependable means of defense than coal-tar, I began a correspondence 

 with the vice-president of the Standard Oil Company, in Chicago, and 

 the chief chemist of the refinery of that company, at Whiting. Ind.. 

 as a result of which they kindly had prepared for me samples of 

 petroleum products similiar to road-oils, one of which seemed, on test- 

 ing, to have the precise qualities sought for. 



Four of the most promising of these substances were carefully 

 tested in comparison with coal-tar at Urbana in April, 1911, by pour- 

 ing them on very dry black soil in the insectary of my entomological 

 office, recording temperatures, and noting the effects on the lines laid 

 down. These were the Standard Oil Company's road oil No. 5 (con- 

 taining 50 percent of asphaltic materials), their road oil No. 6 (con- 

 taining 60 percent of asphaltic materials), and their 14-gravity and 

 16-gravity residuum oils. By experiments commenced at 2:30 p. m. 

 April 19 and continued until 8 a. m. of April 22, it was found neces- 

 sary to pour road oil No. 6 three times where nine pourings were nec- 

 essary with No. 5, and 7 pourings with the 16-gravity oil. The tem- 

 peratures of these days, as shown by thermometers placed on the soil 

 in the sun, ranged from 68 degrees F. April 19 to 100 degrees April 

 21, and the exceptional reading of 125 degrees at 1 p. m. of April 20. 



Another series, carried thru nearly two days, from 11 a. m. of 

 April 25 to 7 a. m. of April 27, brought into comparison this No. 6 

 road oil, ordinary coal-tar, and 14-gravity oil. Where coal-tar re- 

 quired pouring thirteen times, once w T as sufficient with No. 6 road oil, 

 and three times was necessary with 14-gravity oil. The results of 

 these experiments led us to use road oil No. 6 in all our extensive 

 operations in 1911. The summer of 1911 proved, however, to be ex- 

 cessively hot and dry, Sparta, for example, showing mean tempera- 

 tures for May five degrees above normal, for June four and a half de- 

 grees, and for July one and three tenths degrees, with a maximum of 

 105 degrees in the shade for July 4 ; while the rainfall fell below nor- 

 mal, 2.44 inches in May, 2.58 inches in June, and 1.78 inches in July. 

 On the extremely hot and very dry earth in the open sun the No. 6 road 

 oil. altho preferable to coal-tar, became too fluid to serve the best pur- 



