. The sanitation of cities. o Z . ^ Q « K-Jo. E S 5 Z En <-J nj ^ c a; ^ M cu <u C Qi ILl -4—1 X c a 40 ©tllatcr Supply anb IRemoval of Sewaae sewage of cities, and the one thing which remainsto be done is to see that sewage wastes are madeunobjectionable before their discharge. This ispractically all that any community should be re-quired to do. The ideal state of affairs toward which Ameri-can sanitarians are working, is to permit all citiesto discharge their sewage into the nearest stream,but require them first to treat it to a degree whichwill preclude the establishment or maintenanc
. The sanitation of cities. o Z . ^ Q « K-Jo. E S 5 Z En <-J nj ^ c a; ^ M cu <u C Qi ILl -4—1 X c a 40 ©tllatcr Supply anb IRemoval of Sewaae sewage of cities, and the one thing which remainsto be done is to see that sewage wastes are madeunobjectionable before their discharge. This ispractically all that any community should be re-quired to do. The ideal state of affairs toward which Ameri-can sanitarians are working, is to permit all citiesto discharge their sewage into the nearest stream,but require them first to treat it to a degree whichwill preclude the establishment or maintenanceof obnoxious conditions in the stream. Rarelyare two problems of this kind found to be sewage of some cities should be treated to afar greater degree than that of others, dependenton the initial pollution of the stream, its mini-mum volume and velocity of discharge, and thedistance to the next city or, more exactly, to theintake of the next water supply. 4. Q E Z c Z 2 o fy-i _1 S rt H 42 CHAPTER IV THE PURIFICATION OF WATERSUPPLIES The treatment of water to improve its appear-ance and quality has been undertaken in variousways for many years. In ancient times, the mostimportant method seems to have been storage;and from observing the effect of natural filtrationthrough sands, along the shores of streams, it isnot improbable that some form of filtration wasemployed at a very early date. The Chinese,from very ancient times, have used sulphate ofalumina for the purpose of improving the appear-ance of water. In modern days, the first largefilter appears to have been placed in service onthe water supply of London, England, in the cholera epidemic of 1849, the filtrationof the entire supply of that city was made com-pulsory. But the existence of disease-bearingbacteria, or germs, was unknown, and the mostimportant office of filtration was not appreciateduntil long after this date. 43
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