Am\Tune  'i9!8nn'  )    Chlorine  as  a  Sterilizing  Agent.  423 
Theory  vs.  Practise. — It  is  apparent  from  the  theoretical  dis- 
cussion that  chlorinated  lime  is  more  efficient  than  liquid  or  gaseous 
chlorine,  and  that  this  agrees  with  practice  is  proven  by  the  com- 
parison of  results  obtained  at  the  Pennypack  Creek  Disposal  Plant 
at  Philadelphia,4  where  it  was  found  that  even  with  proportionately 
larger  amounts  of  gas  it  was  seldom  that  B.  Coli  were  not  present  in 
the  final  effluent. 
The  substantiation  of  the  theory  that  the  efficiency  of  chlorinat- 
ing media  is  affected  by  various  circumstances  is  found  in  the  results 
obtained  by  the  Ministerium  of  the  Interior  of  Italy,  published  under 
the  title  "  Tests  on  the  Purification  of  Potable  Waters  by  Means  of 
Chloride  of  Lime."5    These  results  may  be  tabulated  as  follows : 
1.  While  a  certain  water  infected  with  B.  Coli  is  sterilized  within 
5  minutes  by  2  p.p.m.  CI  at  400  C.  (1040  R),  6  p.p.m.  are  required 
at  5°  C.  (410  F.). 
2.  The  addition  of  a  small  quantity  of  sterile  sewage  or  of  any 
organic  matter  to  the  water  may  reduce  or  inhibit  the  sterilizing 
action  of  chlorine. 
3.  Turbidity  counteracts  the  action  of  chlorine ;  the  turbid  water 
of  the  Tiber  is  not  sterilized  by  70  to  80  p.p.m.  CI  after  three  to 
four  hours ;  but  after  filtration  with  a  bacterial  content  of  70,000  to 
80,000  per  Cc,  it  is  sterilized  by  1  to  2  p.p.m.  CI  in  fifteen  to  twenty 
minutes.    Small  particles  of  whatever  nature  serve  as  protectors. 
4.  The  salts  in  solution  favor  sterilization ;  hard  waters  are  more 
easily  sterilized  than  soft  waters. 
5.  Chlorine  may  be  regarded  as  initiating  cytolysis  in  germ  cells 
through  oxidative  (?)  changes  beginning  on  the  surface  and  pro- 
gressing towards  the  interior  possibly  accelerated  by  alkalinity  and 
OH  ions. 
From  the  public  health  standpoint,  chlorination  as  a  means  of 
sterilization  is  far  from  ideal,  for  its  action  is  dependent  upon  too 
many  uncontrollable  circumstances,  such  as  diffusion,  the  characteris- 
tics of  the  liquid  and  changes  in  temperature. 
W.  R.  Copeland6  calls  attention  to  this  feature  as  follows : 
The  good  results  obtained  in  summer  time  create  the  impression  in  the 
minds  of  the  average  person  that  water  treated  with  bleach  or  liquid  chlorine 
is  safe  to  drink  at  all  times.    As  a  matter  of  fact,  quite  the  contrary  may  be 
4  Mun.  Jour.,  3,  16,  19. 
5  Ch.  Abs.,  vol.  "12.  No.  4. 
6  E.-N.  Rec,  9,  16,  16. 
