1916] RURAL ENGINEERING. 389 



The sewage of small cities was found to contain the maximum amount of 

 colloids about noon, while purely domestic sewage contained more colloids in 

 the morning. The colloid content comprised from one-third to one-half of the 

 total organic content. An exchange of organic sewage colloids with inorganic 

 colloids of the filtering material was established. It was found that the soils 

 were able to adsorb considerably weaker colloids than the crystalline powder. 

 Colloid adsorption by soils was effected not only by their crystalline constitu- 

 ents but also by their amorphus constituents. By washing out the soils with 

 water the salts were first removed and then the colloids. The greatest part of 

 the soil colloids was found to be of an inorganic nature, even in the moor and 

 humus soils. 



The soils adsorbed organic colloids before inorganic colloids and exchanged 

 inorganic soil colloids for the organic putrefactive sewage colloids, so that con- 

 siderably more organic colloids were fixed by the soil than their theoretical 

 adsorptive powers indicated. Freezing and drying of soils strongly increased 

 their peptonizing powers, especially soils rich in humus. 



The colloids fixed on the surfaces of soil particles in their turn adsorbed 

 molecularly dissolved substances whereby a more extensive power of adsorp- 

 tion of the soil for colloids was reached. 



These results are taken to indicate that the colloid adsorbing properties of 

 soils are the primary factors in the purification of sewage by soils, and that 

 they act in connection with the secondary purification processes involving 

 catalytic and bacteriological influences through the agencies of which adsorbed 

 organic colloids are decomposed and mineralized. Further experiments along 

 this line are in progress. 



Stream pollution and sewage disposal in Illinois with reference to public 

 policy and legislation, L. K. Shekman {III. Rivers and Lakes Com. Bui. 16 

 (1915), pp. SO). — This report deals with stream pollution and sewage treatment 

 and reviews the laws governing stream pollution of Illinois and other States. 



Second annual report of the engineer of the Oregon State Highway Com- 

 mission for the year ended November 30, 1915, E. I. Cantine (Ann. Rpt. 

 Engin. Oreg. Highivay Com., 2 {1915), pp. 90, pi. 1, figs. 16). — This reports high- 

 way construction and expenditures in Oregon for the year ended November 30, 

 1915, as conducted by the engineer of the state highway commission. 



Road maintenance in the several States (Municipal Jour., 40 (1916), No. 14, 

 pp. 465-479, figs. 3). — The reports of 20 state highway commissioners, engineers, 

 or other officials are given, describing the methods most successfully employed 

 by each in maintaining the roads of his State, together with a statement of 

 opinion concerning the importance of road maintenance. 



Maintenance of Indiana highways, G. E. Maetin (Purdue Univ., Bept. 

 Engin., Highway Bui. 1 (1915), No. 1, pp. 24, figs. 10). — The purpose of this 

 bulletin is to present the best current practice in road maintenance operations, 

 with special reference to the roads of Indiana. It is stated that part of the 

 material was drav.n from publications of the Office of Public Roads of the 

 U. S. Department of Agriculture. 



Economics of highway engineering, L. I. Hewes (Cornell Civ. Engin., 24 

 (1916), No. 6, pp. 237-246). — The author discusses road administration, finance, 

 cost, traffic, and cost comparison for different types of surfaces, with reference 

 to their bearing on highway engineering economy. 



Construction field books for bituminous macadam highways, J. T. Ckaw- 

 FORD (Good Roads, 49 (1916), No. 14, pp. 164-166, figs. 4).— Construction field 

 books, the objects of which are to show the highway as planned, staked, and 

 constructed, are described and illustrated, including a grade book, culvert book, 

 stone course book, and a bituminous material book. A book for the engineer 



