1916] 



EURAL ENGINEERING. 



685 



which it Is stated may be applied to even the largest streams. Examples are 

 given based on the actual discharge of several rivers. 



Control of the Colorado River as related to the protection of Imperial 

 Valley, J. C. Aultson {Proc. Amer. Soc. Civ. Engin., 42 (1916), No. 5, pp. 681- 

 709, figs. 10). — The more important details of this work are described. 



The drainage of the humid and saline soils of the Egyptian Delta, III. 

 Catzeflis (Egypte Contemporaine, No. 27 (1916), pp. 324-354, pi. 1). — This 

 article deals with the technique and economics of the drainage of the humid and 

 saline soils of Egypt. 



The results of physical tests of road-building rock, P. Hubbabd and F. H. 

 Jackson, Je. (U. S. Dept. Agr. Bui. 370 (1916), pp. 100, . i).— This bulletin 

 and Bulletin 347 (E. S. R., 34, p. S90) together constitute a complete revision 

 of Office of Public Roads Bulletin 44 (E. S. R., 27, p. 587), and furnish the 

 results of physical tests of road-building rock made in the laboratories of the 

 United States Office of Public Roads and Rural Engineering to January 1, 1916. 

 It has been assumed that traffic of less than 100 vehicles per day is light, 

 between 100 and 250 moderate, and over 250 heavy. 



" The ideal rock for the construction of a water-bound macadam road resists 

 the wear of traffic ... to that extent which will supply a sufficient amount of 

 cementitious rock dust to bind the larger fragments in place. ... As deter- 

 mined by test, cementing values [for rocks] below 25 are called low ; from 26 

 to 75, average ; and above 75, high. In general, the cementing value should run 

 above 25. For rocks which show a low French coefficient of wear, a relatively 

 high cementing value is more necessary than for those which have a high French 

 coefficient. . . . 



" Experience has shown that in general ftie following table of limiting values 

 for the French coefficient of wear, toughness, and hardness may be used in 

 determining the suitability of a rock for the construction of the wearing course 

 of a macadam road : 



Limiting values of physical tests of rock for water-bound macadam road 



construction. 



Character of traffic. 



Limits of tests. 



French coefScient of wear. 



Tough- 

 ness. 



Hard- 

 ness. 



Light.... 

 Moderate 

 Heavy . . , 



&-8— (5-8 per cent wear) 



8-15= (2.7-5 per cent wear) 



Over 15= (less than 2.7 per cent wear) 



5-9 



10-18 



Over 18... 



10-17. 

 Over 14. 

 Over 17. 



"As a result of comparing hardness and toughness tests of some 3,000 samples, 

 . . . when any given value for toughness falls within certain limits which 

 define the suitability of the material for macadam road construction under given 

 traffic conditions, the corresponding value for hardness will fall within similar 

 limits for hardness. . . . The great majority of samples having a French 

 coefficient of wear of from 5 to 8 and a hardness of over 17 are granites, 

 quartzites, and hard sandstones, which are unsuited for use in the wearing 

 course of water-bound macadam roads due to their lack of binding power. 



"For broken-stone roads which are maintained with dust palliatives, the same 

 limits for French coefficient of wear and toughness should hold as for ordinary 

 macadam roads. In bituminous work in some cases it is advantageous to use 

 a rock of relatively high absorption rather than one with low absorptive quali- 



