BUREAU OF PUBLIC ROADS. 493 



leading them to use modern explosives, and has shown many that 

 some work formerly done by hand labor could be done much more 

 efficiently by the use of explosives. North Carolina, for instance, re- 

 ports that every farmer from whom they have secured a report states 

 that after using the supply of picric acid, he had purchased com- 

 mercial explosives to continue the work. 



It^ is estimated that the use of picric acid instead of commercial 

 explosives has resulted in a saving to the farmers who have used it 

 of approximately $800,000. 



As soon as the distribution of the picric acid is completed it is 

 planned to undertake the distribution, in a similar manner, of 18,- 

 000,000 pounds of sodatol. Sodatol is a mixture of trinitrotoluol 

 (T. N. T.) and sodium nitrate. Tests indicate that it will be a very 

 satisfactory explosive for land clearing. Bids for preparing and 

 cartridging the sodatol will be opened in July, 1923. As the T, N. T. 

 is stored at the arsenal near Sparta, Wis., and the sodium nitrate at 

 Nashville, Tenn., the freight rate on the sodatol should be much 

 lower than on the picric acid, which it was necessary to ship from 

 Wingate, N. Mex. 



EXTENSION ACTIVITIES. 



The educational extension work has been continued by means of 

 lectures and addresses, motion-picture films, models, and other ex- 

 hibits at fairs and expositions, farmers' and department bulletins, 

 and contributions to the engineering and popular press. 



Ten sets of small models of various types of roads and bridges, 

 especially made for the purpose, were loaned to more than 80 univer- 

 sities and colleges for use in connection with the course in highway 

 engineering. The models were routed to the institutions in accord- 

 ance with a prearranged schedule by the highway education board, 

 on which are represented, in addition to the bureau, the United 

 States Bureau of Education, the War Department, the Societ}^ for 

 the Promotion of Engineering Education, and various industries in- 

 terested in the development of an adequate highway system. Author- 

 ities of the institutions to which the models were loaned reported 

 that the service thus rendered was distinctly helpful and it is likely 

 that the plan will be continued. 



Arrangements have also been made to supply the schools during 

 the coming year with sets of lantern slides especially prepared to 

 illustrate lectures on all the important types of road construction. 

 These slides, accompanied by the outline of a lecture covering each 

 type of road, will be circulated to the institutions desiring them with- 

 out cost, except for expressage. 



In addition to the exhibits displayed at State fairs under the 

 auspices of the office of exhibits, the bureau also prepared large 

 exhibits for various highway conventions and automobile shows. 

 The more important of these displays were made at the annual 

 convention of the American Association of State Highway Officials 

 at Kansas City, Mo. ; the National Good Roads Show lu-ld Tinder 

 the auspices of the American Road Builders' Association in Chicago ; 

 the annual convention of the United States Good Roads Association ; 

 and automobile shows at New York, Chicago, Utica, and Newark, 

 A special exhibit entitled " Three windows on the road," made for 



