224  Purification  of  Drinking  Water.  {^j^mo*1™' 
elimination  of  manual  labor  and  the  introduction  of  mechanical 
devices,  carried  down  even  to  the  opening  and  closing  of  valves. 
Not  a  screw  in  sight — every  valve  regardless  of  size  operated 
quickly  and  without  effort  by  hydraulic  power  under  direction  of 
but  one  man. 
The  cost  of  this  preliminary  filter  plant  was  one  million  dollars. 
The  wonder  is  not  that  it  cost  so  much,  but  rather  that  so  much 
labor  and  material  could  be  furnished  for  that  sum.  These  state- 
ments may  be  regarded  as  extravagant ;  the  work  is  there,  it  invites 
inspection  and  honest  criticism. 
From  the  preliminary  filters  the  water  is  distributed  without 
delay  to  the  final  filters.  They  are  all  covered  under  ground,  this 
latitude  requiring  such  construction.  In  cold  weather  it  would  be 
impossible  to  scrape  a  filter  if  it  were  frozen  or  covered  with  snow. 
While  under  ground  they  are  illuminated  electrically  and  their 
operation  is  conducted  without  hindrance  and  with  comfort  to  the 
men.  Over  the  entrance  to  the  final  filter  is  placed  an  iron  plate 
bearing  this  inscription :  "  Employees  are  forbidden  to  carry  into 
the  filter  lunch,  paper,  tobacco,  or  other  objectionable  substances." 
This  is  a  cast  iron  rule,  both  literally  and  figuratively,  and  it  is 
rigorously  enforced. 
The  final  filters  do  not  offer  much  opportunity  for  improvement, 
they  being  practically  complete  and  a  thoroughly  understood  sub- 
ject. Still  where  there  is  any  chance,  they  are  not  wanting  in 
ingenuity.  Recently  a  successful  attempt  has  been  made  to  wash 
the  sand  without  removing  it  to  the  exterior  of  the  filter.  The 
device  is  operated  by  hydraulic  power,  and  it  saves  the  removal  and 
return  of  the  sand,  the  only  thing  removed  being  the  accumulated 
sediment  which  is  washed  away  through  conveyors  into  the  sewer. 
This  device  saves  much  time  and  maintains  the  sand  in  the  filter 
bed  at  a  permanent  level,  insuring  a  more  constant  working  of 
each  unit.  Through  the  previous  removal  of  suspended  matter  by 
the  preliminary  filter  the  final  rate  of  filtration  has  been  raised  from 
three  to  six  million  gallons  per  acre  per  twenty-four  hours,  just 
doubling  their  capacity.  There  is  ample  room  at  Torresdale  for 
increasing  the  capacity  of  the  plant  to  meet  the  demands  of  the 
future. 
In  the  laboratory  they  are  diligently  engaged  with  microscopes 
and  media,  with  reagent  and  balance  in  eternal  vigilance,  keeping 
track  of  the  functioning  of  each  filter,  seeking  to  uncover  defects 
