280 EXPERIMENT STATION RECORD. [Vol. 43 



It was found that one day is the most suitable period for the erosion test. 

 Exposure to glass lowers the erosive ability of the water. The greater the depth 

 at which the lead is immer.sed in the water, the slower the erosive action. The 

 velocity of erosion falls as time proceeds. Variation in the volume of water 

 does not appreciably affect erosion. For the untreated water the amount of 

 lead eroded varies directly with the area of lead exposeij. Small changes in the 

 area of the water surface produce no appreciable effect on the erosion. 



Erosion readily occurs in waters which contain no carbon dioxid. Such va- 

 riations as occurred naturally in the percentage of carbon dioxid present in 

 the water produced no appreciable effect on the erosion, but the presence of from 

 1 to 2 per cent of carbon dioxid causes a sudden change from erosion to plumbo- 

 solvency. Carbon dioxid dissolves lead more rapidly in the presence of oxygen. 

 Given oxygen, the alkalinity of the water is the principal factor determining 

 the amount of erosion. 



Not only the amount but the kind of erosion depends chiefly on the alkalinity 

 of the water. The addition of small quantities of calcium hydroxid, carbonate, 

 and bicarbonate, or of potassium permanganate, decreases erosion. Calcium 

 bicarbonate is the most effective preventive, as little as two parts per 100,000 

 being generally sufficient. Erosion occurs in the absence of bacteria. The 

 bacteria in the water are not all desti'oyed by exposure to lead for six hours. 



Water powers of the United States {Elect. World, 15 (1920), No. 12, pp. 

 654-659, figs. 6). — An analysis of developed and undeveloped sources of water 

 power in the United States indicates that the total potential water power is 

 59,360,000 h. p., of which only 9,823,540 h. p. is developed. 



Engineering for land drainage, C. G. Elliott {New York: John Wiley d 

 Sons, Inc., 1919, 3. ed., rev., pp. XVIII +363, pi. 1, figs. 65).— This is the third 

 revised edition of this book (E. S. R., 26, p. 588). 



The discussion of the hydraulics of flow in underdrains has been rewritten, 

 and new tables for the discharge of tile drainage have been introduced which it 

 is believed correspond closely to results obtained in practice. A diagram to 

 facilitate the application of Kuttei-'s formula in the design of ditches and canals 

 has been added. Data on the history of drainage, on drainage by pumps, and on 

 the drainage of irrigated lands have also been added. 



Studies of maintenance work on drainage ditches, H. M. Lynde {Engin. 

 Neics-Iiec. 84 {1920), No. 15, pp. 713-715, figs. 2).— Experiments on the clearing 

 for maintenance of a drainage ditch in the flat coastal plain section of North 

 Carolina are reported. The excavated material was sand occasionally mixed 

 with clay and the ditch bottom was solid sand. The conclusion is drawn that 

 such channels should be cleaned every year and the banks at 3 to 5-year in- 

 tervals. The banks should be gone over each year and kept shrubbed as far 

 back as the waste bank. All logs, trees, and stumps, as well as woody growth 

 like willows, should be removed annually from the channel, and low-water 

 channels should be opened through the sand bars. 



Hydraulic-fill dams, A. Hazen {Proc. Amer. Soc. Civ. Engin., 46 {1920), No. 

 4, pp. 525-557, figs. 12). — Methods of testing hydraulic-fill dams are described, 

 and an effort is made to analyze the conditions of stability. It is pointetl out 

 that it is not well to build a hydraulic-fill dam of material of which any large 

 percentage consists of clay or of particles less than 0.01 mm. in diameter, and 

 in general all such particles may well be wasted and excluded from the dam. 



By reducing the construction pool to a minimum, and by controlling it and 

 the quantities of water used for sluicing, the core material may be held to a 

 certain degree of coarseness by wasting all smaller particles. An effective 

 size of 0.01 mm. may reasonably be sought. 



