808  MORE  POISON  IN  SODA.  WATER. 
tain  the  same  reactions  that  I  did,  he  "  added  to  filtrates  2  and 
4  [equivalents  of  my  experiments  8  and  9],  ferro-cjanide  of 
potassium  ;  and,  in  both  cases,  a  fine  blue  precipitate  was  pro- 
duced. Knowing,"  continues  my  correspondent,  «  that  the  soda 
water  came  in  contact  with  iron  in  no  stage  of  its  manufacture 
and  sale,  suspicion  fell  upon  the  water  from  which  it  was  made. 
To  decide  the  point,  half  a  gallon  was  taken  from  the  pump, 
evaporated  and  tested  for  iron,  when  its  presence  was  made 
evident ;  thus  accounting  satisfactorily  for  the  presence  of  iron 
in  the  soda  water."  And  he  queries  whether  the  reaction  ob- 
served in  my  experiments  8  and  9  could  not  have  been  occasion- 
ed by  the  same  cause. 
Having  repeatedly,  yet  contrary  to  all  published  authority, 
obtained  results  from  the  reactions  of  ferro-cyanide  of  potassium 
with  tin,  in  all  respects  the  same  as  those  with  the  filtrate  from  my 
4th  experiment,  I  could  only  suppose  that  tin  was  retained  in 
the  filtrate  by  the  possible  presence  of  some  agent  like  that  of 
chloride  of  ammonium  in  solutions  of  other  metallic  oxides,  &c; 
but  why  should  the  precipitate  with  K+Cfy  be  blue  f 
In  compliance  with  the  suggestion  of  my  friend,  I  obtained  a 
quantity  of  water  from  the  well  used  by  the  manufacturer  of  the 
«  soda  water,"  and  evaporated  it  to  dryness.  On  re-dissolving 
the  residue  in  a  small  quantity  of  dilute  nitric  acid,  and  testing 
the  resulting  solution  with  sulpho-cyanide  of  potassium,  and  with 
ferro-cyanide  of  potassium,  perceptible  indications  of  iron  were 
manifested. 
I  was  now  induced  to  question  the  purity  of  the  tin  experi- 
mented with  on  the  former  occasion.  It  was  obtained  for  pure 
tin.  Parcels  were  subjected  to  the  action  of  acetic  acid  and 
of  nitric  acid.  In  both  cases  the  sulpho-cyanide  and  the  ferro- 
cyanide  just  named,  produced  the  characteristic  indications  of 
iron.  Sulphydric  acid  was  passed  into  an  acetic  acid  solution  of 
the  metal,  and  the  filtrate,  after  boiling,  treated  with  ferro- 
cyanide  of  potassium;  as  formerly,  a  "  blue  tinge,"  or  rather 
pea  green  color  followed 
In  all  probability,  therefore,  the  two  metals  found  in  the  car- 
bonated water  of  the  new  apparatus,  were  lead  (certainly)  and 
iron  instead  of  tin ;  the  iron  being  derived,  not  from  the  ap- 
paratus, but  from  the  water  charged  with  the  gas. 
Jno.  T.  Plummer. 
