ini.'o] BUBAL ENGINEEBING. 589 



lelntively free from nitrates and nitrites, and tliose from limestone regions 

 usually Iiave a clilorid content less than 10 mg. per liter. It is further noted 

 that these waters have a low microhiological content, corresponding to a gen- 

 erally low organic matter content. 



luspeetion of drain tile for the U. S. Reclamation Service, W. L. Dka(;i:k 

 {licchim. lite. [U. S.], 11 (1020), No. 5, pp. 220-231, figs. 2).— Data are reported 

 sjiowing the inconsistency in the variation in both thickness and breaking 

 strength of drain tile from different kilns. These data are taken to iiKlicate 

 liiat the most satisfactory method of determining the crushing strength of a class 

 of tile is to actually test samples rather than depend upon thickness indica- 

 tions. Absorption tests gave fairly consistent results, indicating a maximum 

 allowable absorption for the clay used of about 4 per cent. 



Excerpts from the U. S. Reclamation Service specilications for drain tile are 

 L'iven, together with a description of the testing methods and apparatus used. 

 A sunnniiry of over 800 tests is also given. 



Farm drainage machinery, J. G. Mekrison {Jour. ISlin. Agr. [London'], 26 

 (1020), No. 11, pp. 1080-1088, pis. 7, figs. 4).— This article describes and illus- 

 trates various classes and types of machines successfully employed in England 

 and elsewhere in the construction of farm drains, Including particularly plows 

 and scoops, wheel and endless-chain excavators, steam tackle, and scraper 

 excavators. 



Eartliwork and its cost, H. P. Gillette (Netv York and London: McGrato- 

 HUl Book Co., Inc., 1020, 3. ed., pp. Xyi+13J,6, figs. 58).— This is the third 

 revised edition of this liaiulbook. It contains a large amount of practical work- 

 ing data on earthworks, methods of fill and excavation, machinery and equip- 

 ment, and cost data. 



The following chapters are included: Properties of earth; measurement, 

 classification, and cost estimating; boring and sounding; clearing and grubbing; 

 loosening and shoveling earth; spreading, trimming, and rolling earth; hauling 

 in barrows, carts, wagons, and trucks; methods and costs with elevating graders 

 and wagon loaders; methods and costs with scrapers and graders; methods and 

 costs with cars; methods and costs with steam and electric shovels; methods 

 and costs with grab buckets and dump buckets; methods and costs with cable- 

 ways and conveyors; methods and co.sts with drag-line scrapers; methods and 

 costs of dredging; methods and costs of trenching; ditches and canals; 

 hydraulic excavation and sluicing; road and railroad embankments; design and 

 construction of earth dams; dikes and levees; and slips and slides. 



Measuring upward pressure under a masonry dam, E. W. Lane and E. L. 

 Chaxdlek (Engin. Neus-Rcc, 8/f (1920), No. 21, pp. lOlIf-1016, figs. //).— Piezo- 

 metric measurements of the upward pressure under a masonry dam on a porous 

 fomidation. consisting of sand and gravel and a slight intermixture of clay, 

 showed that gas was accumulating in considerable quantities beneath the dam. 

 Tlu^ dam, because of its shape, acted as a gas holder and the gas increased the 

 upward pressure. It was found in general that a considerable drop in pres- 

 sure was caused by the upstream sheet-piling and a lesser one by the down- 

 stream piling. 



" From these experiments it seems evident that although sheet-piling and 

 cut-off walls are of value in reducing upward pressures, their effect is not neces- 

 sarily in accordance with the line of creep theory. The results obtained are 

 j)robably not representative of conditions existing immefliately after the closure 

 of the dam, and it is therefore concluded that the greatest danger exists when 

 the head against such a structure is first accumulated. The upward pressure 

 may soon be reduced to an unimportant factor, the length of time required to 

 bring about the change being dependent upon the rapidity with which silt is 



I 



