EUEAL ENGINEERING. 489 



nized in the Rideal-Walker method, apiiaratus and materials, the method of con- 

 ducting the Rideal-Wallver test, the choice of a test organism, the introduction 

 of organic matter, further methods of bacteriological examination, the report of 

 the disinfectant standardization committee, and the llideal-Walker coefficient. 



RURAL ENGINEERING. 



Progress reports of experiments in dust prevention and road preservation 

 {U. »S'. Dvpt. Agr., Office Pub. Roads Circ. 92, pp. 32). — Experiments conducted 

 during the summer of 1909 are reported, together with supplementary observa- 

 tions on experiments previously noted (E. S. R., 21, p. 185. 



From five trials at Washington, D. C. of waste sulphite liquors on a macadam 

 driveway, it is concluded that " crude waste sulplaite liquor in single applica- 

 tions has but little value for road treatment, but that the concentrated material 

 may be classed as a temporary or semipermanent dust preventive and road 

 binder. It is possible, however, that, if crude liquor were applied daily as in 

 ordinary water sprinkling, its use would prove economical in localities where it 

 is produced, and that the base would concentrate in the road and eventually 

 become a valuable binder." 



In seven tests at Youngstown, Ohio, to determine the best method of utilizing 

 slag for road construction, the cost per square yard ranged from 43.34 cts. to 

 51.96 cts. with slag screenings, and was 50.21 cts. with open-hearth slag screen- 

 ings, 4S.1S cts. with slag screenings and lime, G1.31 cts. with slag screenings and 

 sulphite liquor, and 68.45 cts. with refined coke-oven tar. Aside from a tendency 

 in one trial with slag screenings and macadam to calk up or become crumbly 

 under traffic, all these materials produced well-bonded roadbeds. 



A series of 14 experiments was made at Ithaca, N. Y., in cooperation with 

 Cornell University, for the purpose of ascertaining the relative value of dif- 

 ferent road binders under various conditions. The materials used were tar, oil, 

 artificial asphalt preparations, brick, cement, and slag, and in experiments with 

 the bitumens an attempt was made to try out all materials by both penetration 

 and mixing methods. The total cost per square yard in each case was as fol- 

 lows: Penetration method, refined coal tar 45.92 cts., refined semiasphaltic oils 

 49.32 and 52.30 cts., semisolid refined semiasphaltic oil 43.32 cts., refined water- 

 gas tar 46.95 cts., and refined water-gas tar -(sing) 62.87 cts.; mixing method, 

 refined coal tar 56.02 cts., and artificial oil asphalt 58.62 and 60.89 cts.; and for 

 concrete, 74.77 cts. with cement concrete, 85.72 cts. with bitumen-coated cement 

 concrete, and 48.41 cts. with ;ish cement concrete. All of the sections were in 

 excellent condition when last inspected. 



Supr)lementary observations made July 22, 1909, of the experiments started 

 at Newton, Mass., about 11 months earlier, showed that the sections where a 

 flush coat of bitumen had received 0.71 gal. per square yard of asphaltic prep- 

 aration were in first-class condition, whereas those receiving only 0.54 gal. per 

 square yard had required considerable i)atching or the surface was in rather 

 poor condition. A section bound with residual oil was just beginning to pick up 

 under traffic and the oil showed a lack of adhesiveness. Two sections on which 

 refined water-gas tar had been used were in excellent condition, and one which 

 had received a molasses-oil-lime combination had just started to pick up under 

 traffic at a rather sharp curve. 



From the observations made February 19. 1910, of the earth-iisphalt road at 

 Independence, Kans., it is concluded that " the asphalt mixed with the earth ren- 

 ders it fairly impervious to water ; that it acts sufficiently well as a binder to 

 prevent the washing of ruts on grades; that an asphalt having a melting point 

 higher than that used should be emi)loyed if a satisfactory road is to be had in 



