PUBLIC HYGIENE AND SANITATION 407 



710. The cesspool. A cesspool is a hole in the ground 

 for receiving sewage and, usually, for allowing it to soak 

 into the soil. A double cesspool is of advantage, so ar- 

 ranged that solid matters will remain in the first cesspool, 

 and only liquids pass into the second. In a properly act- 

 ing cesspool there are a few inches of sediment in the 

 bottom and a layer of floating solids, neither of which 

 increases in quantity, for decay takes place and destroys 

 and liquefies the solid matter in much the same manner 

 as though it were buried in the soil. 



Chloride of lime and other antiseptics used in the bath room hinder 

 the process of decay, and cause the cesspool to become stopped up with 

 solid matter. In a sandy soil a pair of cesspools, each seven feet in 

 diameter and seven feet deep, should dispose of at least two hundred 

 gallons of sewage daily, or as much as a large family produces. Cess- 

 pools work well in sandy soil where there is an abundance of room and 

 no danger of contaminating the water supply. 



711. A sewer system. In the simplest and oldest sewer 

 systems the untreated sewage is emptied into the nearest 

 body of water. In order that sewage may not be detected 

 by the senses, it must be mixed with an amount of flowing 

 water at least two hundred times as great as its own 

 volume. But the river which receives the sewage is made 

 unfit for use as a source of water or of ice supply, even 

 when the dilution is far greater. In order that sewage 

 may not be a menace to public health, it must usually 

 undergo treatment at a disposal plant. 



An old form of sewage disposal is treatment with chem- 

 icals; but this is costly, and the final disposition of the 

 solids formed by the chemicals is often difficult. 



Another old plan is to maintain a public farm on which 

 the sewage supplies both irrigation and fertilizer. One 

 acre of sandy land will soak up the untreated sewage of 



