AmAJp0r^r;lP8S^m•}    Nitrates  and  Ammonia  in  Water.  159 
phuric  acid,  with  the  hope  of  discovering  some  means  for  prevent- 
ing off-colors,  or  at  least  correcting  these  when  produced.  The 
reagents  were  repeatedly  tested,  but  it  was  impossible  to  attribute 
the  discoloration  to  them ;  among  the  usual  water  constituents 
organic  matters  were  most  likely  to  cause  the  difficulty,  and  the 
attempt  was  made  to  purify  the  water  by  precipitation  with  alum 
before  testing  for  nitrates,  but  this  did  not  give  the  expected 
results. 
The  following  process,  however,  has  been  successful  as  far  as  it 
has  been  tried,  and  depends  upon  the  volatilization  of  the  nitric 
acid  when  the  water  residue,  in  a  duplicate  test,  is  heated  for 
some  minutes  with  sulphuric  acid. on  a  water-bath,  while  the  organic 
matter  is  acted  upon  by  the  sulphuric  acid  to  produce  the  substances 
causing  the  off-color ;  in  the  test  proper  the  nitric  acid  reacts  to 
form  a  nitro-derivative,  while  the  organic  matter  is  acted  upon  as  in 
the  duplicate  test;  two  solutions  are  therefore  obtained,  one  repre- 
senting only  the  color  due  to  the  organic  matter,  whilst  the  other 
contains  additionally  the  color  due  to  the  nitro-derivative ;  by  suit- 
ably diluting  these  solutions  and  adding  to  the  former  sufficient  of 
the  standard  nitro-solution  until  the  two  solutions  are  matched,  the 
quantity  of  nitrates  can  be  determined. 
The  manipulation  is  as  follows :  Two  portions  of  the  sample  of 
10  c.c.  each  are  evaporated  to  dryness  in  small  porcelain  capsules 
on  the  water-bath  (mark  the  tests  I  and  II);  to  I  add  1  c.c.  strong 
sulphuric  acid  ;  to  II  add  1  c.c.  phenol-sulphonic  acid;,  mix  thor- 
oughly with  the  water-residue  and  heat  on  the  water-bath  for  five 
to  ten  minutes;  then  add  to  I  1  c.c.  phenol-sulphonic  acid,  and  to  II 
1  c.c.  strong  sulphuric  acid  ;  mix  thoroughly  and  heat  on  the  water- 
bath  for  five  minutes ;  add  to  each  5  c.c.  distilled  water,  then  10  c.c. 
water  of  ammonia  (drop  by  drop),  and,  lastly,  dilute  with  water  to 
the  same  volume  (the  volume  must  be  such  that  both  of  the  result- 
ing solutions  will  be  much  lighter  in  color  than  the  standard  solu- 
tion, made  as  previously  described ;  transfer  the  entire  solutions  or 
aliq  iot  portions  of  each  solution  to  cylinders  or  test, tubes  of  equal 
inner  diameter  (to  obtain  equal  columns  of  the  liquids  from  the 
same  quantities)  and  add  to  the  lighter  colored  solution  (I)  meas- 
ured quantities  of  the  standard  solution,  to  (II)  add  the  same 
quantities  of  distilled  water  until  the  contents  of  the  cylinders  or 
test  tubes  match  each  other  in  color.    Note  the  quantity  of  stand- 
