230  Chemical  and  Sand  Filtration.        f  Am  jour.  Pha™. 
^  I       May,  1910. 
this  about  in  a  chemical  way  as  follows  :  Calcium  hypochlorite  in 
solution  was  introduced  into  the  water  before  filtration  in  the  pro- 
portion of  two  or  three  parts  per  million.  The  reaction  that  follows 
is  precisely  the  same  as  that  employed  in  urinalysis  in  the  estimation 
of  urea  in  which  nitrogen  is  evolved  as  gas.  The  result  of  this  as 
compared  with  the  oxidation  change  in  the  slow  sand  filter  is,  in- 
stead of  forming  nitric  acid  and  increasing  nitrates,  the  nitrogen, 
as  gas,  is  thrown  off  and  hydrochloric  acid  is  produced,  increasing 
chlorides.  Other  changes  are  the  same.  In  addition  to  this  the 
hypochlorite  has  the  effect  of  increasing-  the  bacterial  efficiency  to  an 
extraordinary  degree. 
Another  interesting  adaptation  of  this  method  of  filtration  may 
be  cited  in  conditions  such  as  are  met  in  the  Passaic  River,  New 
Jersey,  at  Passaic.  The  water  of  the  river  at  this  city  is  black, 
colored  by  the  refuse  discharged  into  it  from  the  silk  dye  works  at 
Paterson.  In  addition  to  the  dye,  all  of  the  sewage  of  the  City  of 
Paterson  empties  into  this  stream,  forming  a  malodorous  combination. 
The  problem  was  to  deodorize  and  decolorize  the  water  and  to  free 
it  from  bacteria  to  a  large  degree.  The  first  was  accomplished  by 
aeration  and  sedimentation.  The  second  by  taking  advantage  of 
the  property  of  aluminum  hydrate  to  form  lakes  with  dye  colors, 
that,  becoming  insoluble  in  water,  are  easily  filtered  out  and  these, 
together  with  the  bacteria,  were  readily  removed  by  the  filter,  work- 
ing at  a  rate  of  1000  cubic  feet  of  filtered  water  per  square  foot 
per  twenty-four  hours.  The  water  resulting  from  this  treatment  was 
suitable  for  use  in  bleaching  wmite  goods  and  the  manufacture  of 
white  paper. 
Another  problem  quite  different  was  met  in  the  treatment  of  the 
water  supply  at  Fort  Hancock,  Sandy  Hook,  New  Jersey.  This 
water  was  so  strongly  impregnated  with  iron  that  it  was  altogether 
unfit  for  drinking.  Tea  was  turned  into  ink,  and  for  laundry  pur- 
poses it  was  impossible.  The  Government  engineers  had  endeavored 
to  free  it  by  oxidation  and  sedimentation,  but  it  was  found  that  all 
of  four  days  were  required  for  oxidation  and  not  less  than  two 
weeks  were  necessary  for  complete  sedimentation,  conditions  that 
were  altogether  impracticable.  Finally,  the  chemical  filter  was  in- 
stalled. The  water  was  treated  with  small  quantities  of  calcium 
hydroxide  in  solution  and  then  filtered  at  the  rate  of  400  million  gal- 
lons per  acre  per  twenty-four  hours,  which  is  equal  to  10  cubic  feet 
in  twelve  minutes  per  square  foot  of  surface  as  compared  with 
