Am.  Jour.  Pharm. 
March.  1904. 
Methods  of  Water  Analysis. 
103 
Carbon — Carbon  dioxide. 
Organic  matter 
{  Ammonia  \  ( 
1  U 
Nitrous  acid 
(Nitrites) 
Water 
Nitric  acid 
(Nitrates). 
This  process,  may  it  be  remarked  in  passing,  is  a  beneficial  one, 
since  by  its  means  purification  of  polluted  water  is  accomplished  and 
the  decaying  organic  matter  converted  into  useful  plant  food. 
These  changes,  under  favorable  conditions,  take  place  incessantly 
so  long  as  there  is  a  supply  of  dead  organic  matter  and  the  neces- 
sary bacteria  are  present.  Therefore,  the  amount  of  organic  matter 
in  water  represents  that  portion  which  has  not  yet  undergone  disin- 
tegration— the  organic  nitrogen  or  so-called  albuminoid  ammonia — 
as  well  as  the  various  intermediary  products  of  the  portion  which 
has  undergone  or  is  undergoing  disintegration — free  ammonia, 
nitrites  and  nitrates.  The  quantitative  relation  of  these  products  of 
oxidation  to  each  other  as  well  as  to  the  unoxidized  nitrogenous 
matter  will  depend  on  the  original  amount  of  the  organic  matter 
and  the  rapidity  with  which  oxidation  has  taken  place.  Therefore, 
an  analysis  which  discloses  these  various  stages  of  oxidation  reveals 
also  not  only  the  presence  but  the  retrogressive  course  of  the 
organic  matter.  Given  a  water  containing  relatively  large  amounts 
of  albuminoid  and  free  ammonia,  together  with  nitrites  and  nitrates, 
the  indications  would  be  that  such  water  contains  a  large  amount  of 
organic  matter  in  a  state  of  incomplete  oxidation ;  in  other  words, 
the  contamination  is  recent.  On  the  other  hand,  the  presence  of 
nitrates,  in  the  absence  of  nitrites,  with  only  small  amounts  of  free 
and  albuminoid  ammonia,  would  indicate  complete  oxidation  or  a 
previous  pollution.  It  goes  without  saying  that  pure  water  should 
contain  only  traces  of  albuminoid  and  free  ammonia  and  should  be 
free  from  nitrites  and  nitrates,  the  latter,  if  in  small  quantity,  being 
rapidly  appropriated  by  the  water  plants.  It  is  to  be  expected  that 
in  deep  wells  removed  from  the  possibility  of  pollution,  the  water 
will  contain  very  slight  amounts  of  ammonia  and  no  nitrites  or 
nitrates,  or  mere  traces,  although  free  ammonia  may  sometimes  be 
present  in  large  amounts  as  a  result  of  oxidation  of  vegetable  matter 
or  nitrates  by  ferric  oxide. 
In  addition  to  organic  matter,  water  contains  various  salts,  the 
most  important  and  constant  of  which  is  sodium  chloride  or,  occa- 
sionally, magnesium  and  calcium  chloride.  These  chlorides  are 
derived  from  the  sea  or  geological  formations  rich  in  salts.  The 
