PURIFICATION  OF  WATER  SUPPLIED  TO  TOWNS.  435 
brownish  incrustation  has  a  strong,  offensive,  marshy  smell.  If 
side  by  side  with  the  spring  water  there  be  exposed,  in  a  similar 
glass  vessel,  the  same  water,  previously  softened,  the  softened 
water  will  continue  for  weeks  and  months  unaltered,  while  that 
unsoftened  water  is  becoming  more  and  more  contaminated  by 
vegetation. 
So  long  back  as  1851,  the  commissioners  appointed  to  report 
on  the  quality  of  the  water  supplied  to  London,  remarked,  that 
"  it  appeared  to  be  only  a  question  of  time,  when  the  sense  of 
the  violation  of  the  river  purity  (by  town  drainage)  would  decide 
the  public  mind  to  the  entire  abandonment  of  the  Thames  as  a 
source  of  supply,  unless  artificial  means  of  purification  were 
devised  and  applied."  They  also  stated,  "that  a  careful  series 
of  experiments  left  no  doubt  in  their  minds  that  the  means  of 
conducting  this  process  are  certain  in  their  results,  and  suf- 
ficiently simple  to  be  left  to  the  execution  of  a  workman  of  or- 
dinary intelligence,  that  the  process  falls  easily  into  the  routine 
operations  of  water-works  ...  is  not  attended  with  any  pecu- 
liar difficulty  on  the  large  scale,  and  that  the  softening  of  Thames 
water  in  its  ordinary  condition  by  this  process  is  perfectly  practi- 
cable, at  a  cost  which  would,  on  the  average,  increase  the  price 
charged  to  the  consumer  only  four  per  cent." 
Nevertheless,  there  is  only  one  instance  in  which  this  process 
has  been  applied  to  the  purification  of  water  supplied  for  general 
purposes.  At  the  Plumstead  Water-Works,  near  Woolwich,  it 
has  been  in  successful  operation  for  the  last  year  and  a  half. 
The  water  supplied  by  this  Company  is  derived  from  the  chalk 
by  boring,  and  has  about  twenty  degrees  hardness,  which  is  re- 
reduced  to  eight  degrees  by  limeing.  The  works  are  capable  of 
supplying  600,000  gallons  daily,  and  at  the  present  time  about 
3?000  houses  are  supplied. 
Eight  months  after  the  Plumstead  Water  Company  had  been 
carrying  on  the  softening  process  with  success,  and  much  to  the 
satisfaction  of  the  consumers,  it  occurred  to  the  Company  to  try 
how  far  the  consumers  would  continue  to  be  satisfied  with  the 
water,  if  the  softening  process  were  omitted. 
The  consequence  was  that  by  the  twelfth  day  the  surface  of 
the  unsoftened  water  in  the  reservoirs,  though  daily  renewed, 
was  covered  with  masses  of  conferva  to  such  an  extent,  that 
