.1 (^rr.sTiox OF priujc iii.m.tu 



147 



still inorc riipid proccsst^s li;i\c Ixcn dcxiscd to iiicct tlic needs of eoiii- 

 iimiiities wliicli li;i\(' no ;iiiii)le s;ind ;ire.is at tlieii- doors. It was shown hy 

 a srrirs ot' Kiijilisli iiiNt-sti^^ators that the nitrilyinti- bacteria could he j;ro\vn 

 on coarser materials like broken stone as well as on sand and that by {illin<i; 

 a l)ed with such materials and let tiny- sewayc stand in it for a short time in 

 ctiiitact with the stone, a considerable purification would take place. Such 

 a purifyiiiii- tle\ice is known as a. "contact bed." 



Till' most cflicicnt de\ ice of all is the "tricklinu" or " pcrcolatini;" bed 

 which reprcsi'iUs still anotlici' method of combinini;- the three re(|nired 



Picking up pollutud driftwood on tlio nattery stops. Moticl in the .Vnii-rican Museum 



elements, sewage, bacteria and air. In 1S94, at Xewport, Rhode^Island, 

 the late Colonel (ieor^e E. Waring' e.\])erimented with the purit'yintr of 

 sewage at hi<;li rates by blowim;- air into a bed of coarse stone from below, 

 wln'le sewage ran down through it from abo\c. Theoretically good, prac- 

 tically the method fell sliort of perfection; but success has finally been 

 reached along another similar Hnc by apj)l\ ing sewage, not in bulk, but in 

 a fine spray flistributed as i-venly as possible over the surface of the bed. 

 liy this method the liipjid trickles in thin films o\er the surface of the filling 



