1917] RURAL ENGINEERING. 287 



wastes, and to illustrate some practical designs for sewage-disposal plants foF 

 construction by the average householder which are the results of experiments 

 at the engineering experiment station. 



It is pointed out that " septic tanks are only water-tight cesspools provided 

 with an overflow. ... A septic tank is only a receiving tank for the sewage 

 in which the solid material is settled out and allowed to remain for 'septic' 

 (i. e.. liacterial) action. Experience has sliown that certain provisions as to 

 size, sl;ape, and structural details will facilitate the proper operation of such 

 a tank, although septic action will take place in any receptacle which will 

 retain sufficient liquid to cover the solid material and exclude light and air. 

 . . . Tlie liquid escaping from such tanks, whether through a tile overflow 

 from a tight tank or through the porous soil or rock seams of a ' leaching ' 

 (not water-tight) cesspool, is extremely foul, and is dangerous to life and 

 health." 



Tl'.e two fundamental principles of sewage disposal are said to embody two 

 distinct, supplementary, and equally necessary treatments, as follows: "(1) 

 Septic action, in a properly arranged, water-tight, covered, masonry tank for 

 removing, retaining, and decomposing the solid material contained in the 

 sewage; and (2) filtration and consequent oxidation and nitrification, by means 

 of a properly arranged and maintained area of porous material through which 

 the effluent from the tank is filtered and subjected to bacterial action. 



" In general, it may be said that only approximately one-third of the necessary 

 puriflcnti.jn takes place in the tank. The degree of further purification will 

 depend upon the type of filter chosen, its construction, care, and operation." 



As a current breaker, it was found in the experiments that an ordinary 

 box 12 by 12 by 12 in., open at the top, bolted to the end of the wall of the 

 tank, and receiving directly the downward discharge of the inlet pipe through 

 an elbow on the end, is effective. An upward sand filter at the outlet was 

 found to minimize the passing on of sediment due to disturbance to the filter 

 bed. 



With reference to filters, " experimentation has shown that a bed of i-in. 

 pebbles, with ample provision for its aeration and the even distribution of 

 sewage in small quantities over its surface will do good work and discharge 

 an effluent comparatively free from offensive materials. Willi such beds it is 

 necessary that very special precautions be exercised to insure thorough aeration 

 so that the purifying agencies may have a constant supply of oxygen." Inter- 

 mittent sand filters are also discussed. 



" The size of the dosing chamber is made such that the quantity of sewage 

 discharged will flood the bed to a depth of only about ^ in., this being repeated 

 from two to four times during 24 hours." 



Diagrammatic illustrations of three plants designed at the station are 

 presented. 



Desig'ns for privies, R. Messee (Amer. Jour. Pub. Health, 7 (1917), No. 2, 

 pp. 190-196, figs. 5). — The author briefly describes and illustrates several v/ell- 

 known tyiies of so-called sanitary privies and points out the advantages and 

 disadvantages of each. It is believed " that some modification of the L. R. S. 

 wet closet is the most satisfactory that has yet been suggested, and, further- 

 more, the additional expense of building is more than offset by permanency 

 and small cost of maintenance. That the problem is far from being satis- 

 factorily solved is clearly evident." 



Hydroelectric power. — I, Hydraulic development and equipment; II, Elec- 

 trical equipment and transmission, L. Lyndon (A'ejc York: McG'rai'-IIill 

 Book Co., 1916, vols. 1, pp. VII-\-J,99. pi. 1, figs. 23^; 2, pp. VII +360, figs. 

 Idlf). — This work Is in two volumes. It is the author's purpose "to produce 

 4066— No. 3—17 7 



