KURAL ENGINEERING. 887 



poses. . . . Nitrification is checked if sewage is turned over land in too great 

 quantities or if the air is cold, and if the sewage is applied freelj- there is a 

 tendency to wash out of the soil what nitrates have formed. In considering 

 the fertilizing value of sewage it is also necessary to consider its ingredients 

 which are detrimental to agriculture. The fat and soap may work harm by 

 clogging the pores of the soil and thus counterbalance the small improvement 

 due to the nitrogen, phosphoric acid, and potash. ... In sewage disposal . . . 

 the crops should be regarded as merely a by-product. All evidence furnished 

 by many years' experience in many countries under many conditions does not 

 reveal, however, any decisive proof that it is possible to obtain much fertilizing 

 value from city sewage as it must be used to make irrigation practicable, but 

 indicates that where sewage irrigation has been successful agriculturally, irri- 

 gation with water would have produced about the same results. English ex- 

 perience indicates that whatever profit is to be made in the future from the 

 fertilizing ingredients of sewage will probably result from the production of 

 artificial manures from sludge." 



In a chapter on the disposal of residential and farm sewage, it is stated 

 that " where the desired degi'ee of purification of the sewage is high and the 

 treatment involves methods of filtration which should proceed at fairly regular 

 rates, it is evident that the storage of sewage so as to permit fairly uniform 

 delivery to the filters and some uniformity in the composition of the applied 

 liquid by mixing the laundry wastes, kitchen wastes, and domestic sewage to- 

 gether becomes particularly important. In the second place, the small size of 

 the plants makes it desirable to have them as nearly fool-proof and automatic 

 as possible. Even if the owner's means render economy in management unnec- 

 essary, the importance of automatic operation is great because experience shows 

 that regular attendance is rarely given to these little plants." 



Septic tanks and absorption systems, T. D. Beckwith and T. A. H. Teetee 

 (Oreg. Agr. Col. Ext. Div., Ser. 2, Ko. 8, pp. 18, figs. 9). — This publication deals 

 with the design and construction of small sewage disposal systems, consisting 

 essentially of a septic tank and tile absorption area. The designs are based on 

 the views of both the engineer and bacteriologist. 



It is pointed out that " the septic tank, if made water-tight, can be located 

 anywhere outside the cellar wall without danger of disease or bad odors. . . . 

 The sewer from the house should consist of a 4- to 6-in. vitrified sewer pipe 

 with a trap near the house end to form a water seal in order to guard against 

 the escape of sewer gas into the house." The necessity of compartments in a 

 septic tank is emphasized, and it is stated that " the scum which forms on the 

 surface of the sewage in the first chamber is essential to the proper action of 

 the tank." 



Statements regarding other points of controversy among authorities are made 

 as follows : " The tank becomes nothing more nor less than a large culture 

 chamber for the growth of the proper kinds of bacteria, and upon them solely 

 depends the work of purification of sewage entering the tank. . . . The types 

 of bacteria in a septic tank are two, (1) those which thrive without the pres- 

 ence of free oxygen or air and which demand that the portion of the tank in 

 which they grow must be as nearly air-tight as practicable, and (2) those 

 which require oxygen to thrive and which do their work best in the presence of 

 as much air as possible. The second compartment, where the bacterial action 

 is completed, should be so constructed that air may have free entrance and 

 circulation. ... A septic tank which purifies over 70 per cent is very excep- 

 tional, and generally only from 60 to 65 per cent purification may be expected." 

 41852°— No. 9—16 7 



