560 
Purification  of  Water  Supplies. 
(  &.m.  .lonr.'Ptiarm. 
I   December,  1904. 
been  due  to  causes  not  generally  recognized  at  the  time.  I  am 
aware  that  this  is  a  point  upon  which  the  experts  disagree,  and 
about  as  many  men  can  be  found  who  will  claim  that  copper  is  a 
poison  as  those  who  maintain  that  it  is  innocuous.  It  seems  to  me, 
however,  that  under  the  circumstances,  since  those  who  are  sup- 
posed to  know  cannot  agree  upon  this  point,  that  we  are  justified 
in  taking  what  might  be  termed  the  evidence  of  experience,  and 
basing  our  conclusions  upon  this.  The  very  well-known  fact  that 
copper  is  contained  in  proportionately  considerable  quantities  in  a 
good  many  ingredients  of  our  daily  food,  and  that  this  amount  of 
copper,  while  sometimes  added  artificially,  is  often  naturally  pres- 
ent, should  lead  us  to  the  conclusion  that  certainly  these  infinitesi- 
mal amounts  are  not  harmful.  The  decision  of  the  English  judge 
in  the  case  of  prosecuting  a  dealer  for  using  copper  in  greening 
vegetables  is  worthy  of  note.  Being  somewhat  bewildered  by  the 
large  amount  of  testimony,  the  experts  on  both  sides  were  able  to 
produce,  proving  definitely  both  the  poisonous  and  harmless  nature 
of  this  metal,  he  based  his  decision  upon  the  fact  that  in  a  market 
which  had  been  selling  these  greened  peas  for  thirty-six  years,  and 
had  now  reached  a  number  of  about  20,000,000  cans  a  year,  the 
prosecution  were  unable  to  bring  forward  a  single  case  of  sickness 
or  injury  which  could  be  traced  even  in  the  remotest  way  to  the  use 
of  these  vegetables.  A  can  of  these  peas,  by  the  way,  contains 
several  hundred  times  more  copper  than  would  ever  be  used  in  the 
treatment  of  a  water  supply. 
If  within  the  last  four  or  five  months  over  fifty  water  supplies 
throughout  the  country,  with  reservoirs  varying  from  a  few  to  hun- 
dreds of  millions  of  gallons,  and  which  for  years  have  been  rendered 
unfit  for  use  because  of  algal  pollution,  can  be  successfully  cleared 
up  with  one  or  two  applications  of  copper  sulphate  at  a  dilution  of 
from  one  to  fifty  million,  it  seems  to  me  that  we  are  justified  in 
believing  that  the  method  is  efficient,  and  accomplishes  something 
which,  until  it  was  introduced,  has  been  considered  one  of  the  un- 
solved problems  in  water  supply  work.  Whether  it  is  harmless 
or  not  I  will  not  discuss  further.  This  is  a  question  which 
must  be  decided  by  the  authorities  of  each  community,  and,  of 
course,  if  there  is  any  doubt  on  the  subject,  the  method  should  not 
be  used.  It  does  seem  strange,  however,  that  there  should  be  any 
objection  to  the  possibility  of  taking  into  the  system  a  substance 
