422  Chlorine  as  a  Sterilizing  Agent.  {Am'^e'w%m' 
Two  distinct  processes  take  place  during  the  diffusion  of  the 
chlorinating  media.  The  first  is  the  spontaneous  decomposition  of 
the  hypochlorite,  which  proceeds  to  a  greater  extent  with  chlorine 
than  it  does  with  chlorinated,  lime.  The  second  is  the  oxidation  of 
the  organic  matter,  the  velocity  of  which  is  greater  with  chlorine 
than  with  chlorinated  lime. 
Comparison  of  Chlorine  with  Chlorinated  Lime. — It  has 
been  shown  above  that  the  loss  of  potential  oxygen  is  not  so  great 
with  chlorinated  lime  as  it  is  with  chlorine  and  that  the  velocity  of 
oxidation  is  lower  with  chlorinated  lime.  This  latter  fact  is  im- 
portant because  the  oxidation  of  organic  matter  is  not  selective, 
although  some  substances  are  more  readily  oxidized  than  others. 
Chlorinated  lime,  owing  to  its  lower  reaction  velocity,  will  diffuse 
to  a  far  greater  extent  than  chlorine,  without  having  its  potential 
oxygen  depleted,  and  will  come  in  contact  with  and  destroy  a  larger 
number  of  bacteria.  Therefore,  given  the  same  quantity  of  poten- 
tial oxygen  in  both  cases,  it  is  evident  that  it  will  have  a  higher  bac- 
terial efficiency  in  the  form  of  chlorinated  lime. 
Effect  of  Temperature. — The  influence  of  temperature  upon 
the  velocity  of  reactions  is  usually  very  great,  a  rise  of  io°  C.  fre- 
quently doubling  and  sometimes  tripling  the  velocity.3  An  example 
of  this  kind  is  afforded  by  gaseous  hydrogen  and  oxygen,  which  do 
not  combine  at  a  measurable  rate  at  3500  C,  while  at  6oo°  C.  the 
rate  of  combination  is  so  rapid  that  an  explosion  results. 
It  seems  that  the  velocity  of  reaction  is  nearly  proportional  to 
the  square  root  of  the  absolute  temperature,  being  accelerated  by 
raising  and  retarded  by  lowering  the  temperature. 
When  applied  to  water  supplies,  low  temperatures  account  for 
the  taste,  and  in  some  instances  for  the  odor  of  the  hypochlorites  in 
cold  water,  because  the  reaction  is  retarded  to  such  an  extent  that 
a  large  portion  of  the  hypochlorites  enter  the  system  intact,  not  hav- 
ing acted  upon  the  bacteria  or  organic  matters. 
Applied  to  sewage  effluents,  a  reduction  in  temperature  due  to 
dilution  in  streams  or'  to  cold  weather  would  indicate  that  hypo- 
chlorites would  be  rendered  ineffective  because  of  their  decreased 
reaction  velocity  and  the  high  dilution  to  which  they  are  subjected. 
Where  sedimentation  follows  chlorination,  the  reaction  would  be  re- 
tarded to  such  an  extent  by  cold  weather  that  a  considerable  portion 
of  the  hypochlorites  would  enter  the  stream  intact,  not  having  acted 
upon  the  organic  matters  or  bacteria. 
3  Jones. 
