I Qi'i:sTf().\ or rrin./c iikai.tii 



\a: 



near sewer outlets to t'uriiisli excellent opporl unity lor infection of xarioiis 

 sorts. 



Tlu" first pr()i)lein in the disposal of city sewage is I lie eliniinalion of the 

 coarser floatint;- particles hy some form of screenini;-. In some eases this 

 alone is snilicienl. lull ucnei-ally sediment at ion must also he ein|)loye(l. In 

 sedimentation excellent results lia\(' come from the use of a dee|) tank ha\- 

 \n)l a conical or pyramidal bottom. Into the lower part of this tank the 

 sewage enters, spreads out in the conical section as it rises, prof,n-essi\('ly 

 diminishes in xclocity, and when the efllueiit Hows oil' at the top, lea\cs thi' 

 suspended solids hehind. 



The sludge which aceuiimlates in the sedimentation tank must itself 

 he disposed of in some way and the modified sedimentation hasin known as 

 the " sei)tic tank" is designed to nu'nimize this nuisance hy holding the shxlge 

 under such conditions that it may he li(piified hy anai'M-ohic hacteria. One 

 tank of this type, the IndiolV tank used extensixcly in northern (Germany, 

 has met with marked success. 



. After the remox'al of suspended solids, the liijuid sewage remains to he 

 purified. The most j)rimiti\e method of (lis])osal consists in its distrihntion 

 o\-er the sin-face of suitable land, what is called " hroad irrigation." I'lider 

 proper conditions the li\ing earth renders organic matter harmless and 

 changes it into food material for the higher |)lants. I'ai-is and Berlin to-<lay 

 utilize this method of disposal. Hut hroad irrigation i-cquires large areas 

 of land of suitahle soil and would he a costh' method for a cit\- situated as 



IntiTinitlont ."^and Kilitr Ucd. I'hotogriipli of a iiiuclil in the American Mii.sui 



