190 EXPERIMENT STATION RECORD. [Vol.43 



involves grave possibilities of the pollution of ground water, near-by wells, 

 and even distant springs. It ought never to be indiscriminately recommended 

 for general use, nor should it be installed except under expert advice or under 

 conditions that preclude the pollution of subsurface water supplies." 



Intermittent sand filtration is adapted to small-plant conditions. The filter 

 layer should be of fairly coarse sand, at least 24 in. and preferably 36 in. 

 deep. About 45 sq. ft. of filter surface should be provided per capita if the 

 water consumption is about 100 gal. per capita per day and 30 sq. ft. if the con- 

 sumption is 20 gal. per capita per day, using intermediate areas for intermediate 

 consumption values. 



Contact beds are not recommended for use in small plants, and trickling 

 filters are not adapted to small-plant conditions unless equipped with a sewage 

 distributor which will be free from clogging difficulties. Lath is preferable 

 to broken stone for small trickling filters, because of the greater size and 

 clearness of the voids and the resulting decreased likelihood of clogging diffi- 

 culties in the filter material. The laths are arranged in layers alternately at 

 right angles to each other and with a horizontal clearance of about 3 in. It 

 was found that 8 cu. ft. of such filter material per person is ample to produce 

 a highly oxidized effluent, provided the depth of the filter material is at least 

 42 in. A filter depth of 5 or 6 ft. is suggested where practicable. When pro- 

 tected against low temperatures, it was found that very small trickling filters 

 can be operated efficiently with a total fall as low as 48 in. 



" That type of plant is best for a given case which gives the required degree 

 of purification with the amount of fall and area of land available at the lowest 

 cost and with the least attention. Where ample stream dilution and other 

 local conditi(ins make it sufficient to remove only the settling and floating solids, 

 the Imhoff tank is recommended. Where it is necessary in addition to pro- 

 duce an oxidized effluent, a plant composed of a preliminary ImhofE tank, lath- 

 trickling filter, and final Imhoff tank is in general considered most advantageous 

 from all standpoints, except that of fall required. In situations in which the 

 lack of available fall is the controlling feature, careful consideration should 

 be given to the possibility of pumping the final effluent by water-jet pump or 

 windmill, the difficulties of such procedure beeing conscientiously compared 

 with the possible danger of soil pollution resulting from subsurface irrigation. 

 There are many conditions under which the latter may properly be employed, 

 but the fact can not be overemphasized that these conditions are not capable 

 of exact definition nor of proper determination on the ground, except by an ex- 

 pert, and only then after considerable study. For all these reasons the lath- 

 trickling filter device with suitable tank treatment, as described, is more confi- 

 dently recommended for general use under all conditions than any other sewage- 

 treatment device thus far available for the treatment of residential and small 

 community sewage." 



RURAL ECONOMICS. M 



Renting land in Missouri, O. U. .Tohnson and II, M, Green {Missouri Sta. 

 Bui. 167 {1920), pp. 52, figs. 6).— This bulletin cites data obtained from 848 

 farms, representing, all parts of the State of Missouri for the years 1912-1915, 

 comparing the economic factors concerned in three common systems of renting 

 land (1) for a share of all crops, (2) a share of the crop land and cash for 

 the rest of the farm, and (3) a straight cash charge for the whole farm. Tabula- 

 tions are made of the tenant's capital, yields and methods of renting, live stock 

 on the tenant farm, crops grown, use of labor equipment, returns fronr live 

 stock, source of income, and labor income for each of the three types. The 



