584 EXPERIMENT STATION RECORD. [Vol.35 



Vict Labor for Highway Worlf, by G. P. Coleman; Motor Traffic, Its Develop- 

 ment, Trend, and Effects, by A. W. Gould ; Equipment for Highway Work, by 

 A. H. Blanchard ; Comparisons of Traffic and Their Economic Value, by L. 

 White; Maintenance — Materials and Methods, by A. W. Dean; and Dust Sup- 

 pression and Street Cleaning, by W. H. Connell. 



Grading- aggregates for Illinois concrete roads, A. H. Hunter (Concrete 

 [Detroit, Mich.'], 8 {1916), No. 5, p. 209). — A table giving the present require- 

 ments as to gradation of aggregates for concrete road work in Illinois is given, 

 together with a table of unit costs of several concrete roads built by day 

 labor under the supervision of the Illinois Highway Commission. 



Test of Douglas fir bridge stringers, H. B. MacParland {Bui. Amer. By. 

 Engin. Assoc, 17 {1916), No. 184, Pt- 2, pp. 281-^67, figs. 153; nbs. in Engin. and 

 Contract., 45 {1916), No. 19, pp. 427-430, fig. 1; Engin. Rec, 73 {1916), No. 15, 

 p. //79). — Tests of 61 representative Douglas fir stringers in which the stringers 

 were subjected to a process of creosoting involving boiling under vacuum are 

 described. Nine of the specimens were put to special tests after treatment, 

 while 52 stringers were cut in two and comparative tests made of the untreated 

 and treated halves. 



" A comparison of the results of the transverse tests, applying loads at the 

 third points, of 7 by 16 in. by 14 ft. span treated and untreated stringers 

 shows that of the 52 representative untreated specimens 16 failed by shear, 

 29 by tension, 3 by tension and shear, 2 by crushing and tension, 1 by crushing 

 and shear, and 1 by crushing, while the following numbers of treated stringers 

 failed from the causes noted : Thirty-two shear, 14 tension, 4 tension and 

 shear, and 2 crushing and shear. . . . The average elastic limit of the 

 untreated pieces was 4,269 lbs. per square inch as compared to 3,481 lbs. per 

 square inch for the treated stringers. The average modulus of rupture was 

 5,691 lbs. per square inch for the untreated and 4,680 lbs. per square inch 

 for the treated stringers. The average longitudinal shear for the untreated 

 pieces was 411 lbs. per square inch, which was 78 lbs. per square inch greater 

 than that for the treated specimen. 



" Specimens for the compression tests, applying the load parallel to the 

 grain, were 5 by 5 by 12 in. in size. It was found that the maximum load 

 for the untreated pieces was 4,114 lbs. per square inch and 3,869 lbs. per 

 square inch for the treated blocks. Applying the load perpendicular to the 

 grain of 6 by 6 by 30 in. blocks showed that the treated specimens had an 

 average elastic limit of 322 lbs. per square inch, which was 116 lbs. per square 

 inch less than the average for those that were not treated. The average area 

 penetrated by creosote as determined by this test was 20.41 per cent." 



The following conclusions were drawn : " Moisture may be successfully 

 removed by boiling under vacuum. Moisture determinations show that, on an 

 average, 35 per cent of the total moisture was removed by the process. The 

 removal of moisture by boiling under vacuum, preliminary to creosoting, 

 decreases the physical strength of the material. The weight of creosote per 

 unit of volume for treated material is dependent on the structure of the 

 specimen. Spring wood offers greater resistance to treatment tlian summer 

 wood. Special tests of treated stringers indicate that the decrease in physical 

 strength due to treatment is not confined to the area penetrated by creosote. 

 The entire structure is affected. The compressive strength parallel to the 

 grain was decreased 6 per cent. The compressive strength perpendicular to 

 the grain was decreased 26 per cent. Although the average strength of the 

 treated material is appreciably decreased, its stiffness, as measured by the 

 modulus of elasticity, is not affected. In general, the average strength of 



