EUKAL ENGINEERING. 183 



heated. The remaining 4 are made up respectively of Portland cement concrete 

 pavement, water-bound macadam, asphalt, and a surface application of asphalt 

 and sand on an old macadam strip. 



A large amount of data is given, outlining in detail the methods of construc- 

 tion and the binders used in the various sections, with the unit cost per square 

 yard and daily records of the temperature and traffic census. Because of the 

 excessive cost of constructing a small section of each kind of pavement a com- 

 I>aris3on of costs per square yard was not made. 



Public roads are public necessities, J. H. Pratt (N. C. Geol. and Econ. 

 Survey, Econ. Paper S2, 1913, pj). 62). — This paper consists chiefly of recent de- 

 cisions of the supreme court of North Carolina on the validity of county and 

 township bond issues for constructing public roads, and on the expenditure of 

 funds from the general treasury of the county for this same pui-pose. 



Explosives in agriculture, G. Makes (Agr. Gaz. 2V. S. Wales, 2If (1913), 

 No. 1, pp. 1-18, pis. 6, figs. 16). — From extended observations and experiments 

 the author outlines in detail methods of blasting stumps and trees, and of sub- 

 soiling and planting orchards by the use of gelignite, a high velocity explosive. 



He concludes that no set rule can be applied as to the amount and location 

 of the explosive in stump and tree blasting, as each stump and tree presents an 

 individual problem. For subsoiling he states that holes should be bored from 

 2 ft. 6 in. to 3 ft. deep 16 ft. apart and the charge placed at the bottom. The 

 size of charge varies from IJ to 2 cartridges, depending on the nature and con- 

 dition of the subsoil, and should disturb the soil for a radius of from 8 to 9 ft. 



For the best results it i§ deemed essential that the subsoil be fairly dry since 

 if charges are exploded while the clay is wet or saturated the plastic condition 

 causes it to yield and an excavation is made without the desirable series of 

 fissures. In a diy subsoil the effect of the explosives is seen in the breaking of 

 the clay and openings and fissures are produced in all directions. On slopes 

 care and judgment should be exercised so as not to interfere with drainage, and 

 to make sure that the arrangement of charges is such that the fissures are con- 

 nected. Small charges arranged in lines and fairly close together are preferable 

 to large charges a greater distance apart. 



He states in conclusion that a considerable saving can be effected in cost and 

 time by this method, ranging from 25 to 50 per cent. 



Graphical methods of determining' practical dimensions of retaining and 

 storage walls with the maximum stresses, L. Hauska (Cenfbl. Gesam. 

 Forstw., 39 (1913), No. 2, pp. 66-75, figs. 5).— This is a mathematical and 

 graphical discussion of the subject, which has been applied to the work of the 

 German forestry service. 



Sand cement as used by the United States Beclamation Service (Engin. 

 Neirs, 69 (1913), No. 12, pp. 562, 563). — Investigations and comparative tests by 

 C. H. Paul are reported of sand cement as used in irrigation works and made 

 of an equally blended mixture of sand and Portland cement, finely ground, and 

 of standard Portland cement. The conclusion is drawn that the use of sand 

 cement in mass work where the requirements are enough to justify the installa- 

 tion of grinding machinery, where suitable blending material is available, and 

 where the trans-portation charges on Portland cement amount to a considerable 

 portion of its cost laid down, will result in a marked saving In construction costs 

 and will give a product which is the equal of Portland cement. 



Value of washed sand and gravel in concrete (Cement and Engin, Neivs, 

 25 (1913), No. 3, pp. 88, 89, fig. i).— Comparative tests of the use of washed and 

 unwashed sand and gravel in concrete show a saving in cement by washing 

 and a gain in strength. A mixture of 1 : 3 : 5 of the washed material developed 

 a greater crushing strength in 28 days than a mixture of 1:2:3 of unwashed 



