102 
MetJwds  of  Water  Analysis. 
Am.  Jour.  Pharm. 
March,  1904. 
analysis  which  the  chemist  may  be  called  upon  to  make.  The  find- 
ing of  arsenic  or  some  poisonous  alkaloid  in  a  suspected  fluid  is 
decisive,  and  a  report  on  such  finding  is  merely  a  statement  of  fact. 
In  the  analysis  of  water,  on  the  other  hand,  the  findings  are  purely 
relative  and  must  be  properly  interpreted  before  they  can  be  of  any 
value.  A  drinking  water,  if  I  may  borrow  the  legal  phraseology, 
is  indicted  on  circumstantial  evidence,  and  it  depends  on  the  erudi- 
tion and  ability  of  the  chemist  to  so  interpret  and  connect  the 
evidence  as  to  make  out  a  clear  case  for  or  against  the  suspected 
water. 
The  object  of  a  chemical  analysis  of  water  is  to  discover  whether 
or  not  pollution  with  objectionable  organic  impurities  has  taken 
place.  By  "  objectionable  organic  impurities  "  we  understand  those 
which  are  from  human  or  animal  sources  and  are  capable  of  convey- 
ing the  germs  of  disease.  In  other  words,  we  look  principally  for 
fecal  contamination,  inasmuch  as  the  germs  of  typhoid  fever,  cholera, 
dysentery  and  other  intestinal  disorders  are  excreted  with  the  feces 
and  together  with  the  feces  gain  access  to  the  water.  By  itself, 
organic  matter  in  the  minute  quantities  in  which  it  is  present  in 
water,  is  not  injurious  to  health,  even  if  derived  from  sewage.  It  is 
only  because  this  organic  matter  may  be  the  carrier  of  disease  germs 
that  it  becomes  a  matter  of  serious  consideration.  Therefore,  organic 
matter  derived  from  plants  or  vegetables  removed  from  the  possi- 
bility of  infection  with  disease-producing  bacteria  has  no  significance 
from  a  sanitary  standpoint,  and  its  presence  in  drinking  water  in  no 
way  renders  it  unwholesome. 
It  is  thus  evident  that  the  aim  of  the  sanitary  chemist  is  to  dis- 
cover, first,  the  presence  of  organic  matter,  which  would  indicate 
pollution,  and,  second,  to  determine  the  source  of  this  organic 
matter.  How  well  these  two  requirements  are  fulfilled  by  a  chemi- 
cal analysis  will  be  made  clear  later. 
Dead  organic  matter  in  water,  as  elsewhere,  is  not  in  a  state  of 
stability.  Through  the  agency  oi  certain  bacteria,  in  the  presence 
of  oxygen,  it  continuously  undergoes  material  changes,  becoming 
resolved  into  simpler  inorganic  compounds.  The  nitrogenous  sub- 
stances are  converted  into  ammonia,  and  the  latter  into  nitrous  and 
finally  nitric  acid,  the  two  acids  combining  with  bases  usually  present 
to  form  nitrites  and  nitrates,  respectively.  These  changes  may  be 
best  illustrated  by  the  following  scheme: 
