124  Action  of  Hydrogen  Peroxide.  {AmkJaTch,T892rm' 
aldehyde  and  acetic  ether.  Upon  testing  the  character  of  the  iron 
salt  after  the  mixture  cooled  there  was  found  to  be  present  only 
ferric  salt ;  should  the  test  be  made  before  the  mixture  cools,  or,  if, 
after  having  cooled,  the  mixture  be  warmed  again,  there  will  be  pro- 
duced a  dark  blue  precipitate,  which  might  be  taken  as  an  indica- 
tion of  ferrous  salt  (this  behavior  was  explained  by  subsequent 
experiments ;  the  hydrogen  peroxide  is  not  completely  reduced 
unless  a  sufficient  quantity  of  ferric  chloride  is  present,  in  which  case 
the  undecomposed  hydrogen  peroxide,  aided  by  heat,  reduces  the 
reagent  used  for  the  detection  of  the  ferrous  salt,  potassium  ferri- 
cyanide,  to  potassium  ferrocyanide  and  this  then  gives  a  dark  blue 
precipitate  with  the  ferric  salt  present).  If  to  a  portion  of  the 
solution  ammonia  be  added  in  excess,  the  precipitate  collected  upon 
a  filter,  washed  several  times  with  distilled  water,  redissolved  in 
dilute  hydrochloric  acid  and  then  tested  with  potassium  ferricyanide 
only  the  brown  coloration  due  to  ferric  salts  is  obtained.  If  the 
solution  be  kept  for  a  few  days  and  then  examined  by  addition  of 
ammonia,  there  will  be  produced  a  clear  greenish  solution  which,, 
upon  standing,  will  show  a  brownish  coloration  upon  the  surface,  and 
only  after  some  time  will  there  be  produced  a  precipitate  ;  this  pre- 
cipitate collected,  washed,  dissolved  in  dilute  acid  and  tested  with 
potassium  ferricyanide  will  give  a  very  decided  dark-blue  precipitate 
indicative  of  ferrous  salt.  The  above  method  was  used  to  remove 
the  undecomposed  H202  so  that  this  could  not  interfere  with  the 
test.  From  these  experiments  it  will  be  seen  that  the  ferric  salt  is 
not  immediately  reduced  to  ferrous  salt,  and  that  the  ultimate 
reduction  is  probably  due  to  the  reducing  action  of  alcohol  or  alde- 
hyde since  tincture  of  iron,  after  standing  some  days,  also  gives  a 
test  for  ferrous  salt. 
Further  experiments  proved  that  alcohol  and  glycerin,  either 
alone  or  mixed,  had  no  action  upon  the  hydrogen  peroxide,  but 
that  the  tincture  of  iron  with  the  hydrogen  peroxide  gave  the  same 
results  as  recorded  ;  this  clearly  indicated  that  the  ferric  chloride 
and  hydrogen  peroxide  were  the  reacting  ingredients.  Using  the 
ferric  chloride  solution  with  hydrogen  peroxide  it  was  noticed  that 
heat  was  also  generated  and  that  a  considerable  quantity  of  a  gas 
was  liberated  which,  by  causing  a  spark  on  a  taper  to  burst  into 
flame,  was  proven  to  be  oxygen.  It  now  became  a  matter  of  inter- 
est and  importance  to  determine  the  volume  of  liberated  oxygen 
