Am.  Jour.  Pharm.  \ 
August,  1889.  J 
Soluble  Prussian  Blue. 
429 
SOLUBLE  PRUSSIAN  BLUE.1 
By  C  E.  Guignet. 
Ordinary  soluble  Prussian  blue  is  a  compound  of  Prussian  blue  with 
potassium  ferrocyanide.  It  is  easily  obtained  by  gradually  adding  to 
a  boiling  solution  of  110  grams  of  potassium  ferricyanide  a  hot  solu- 
tion of  70  parts  of  crystallized  ferrous  sulphate.  The  .mixture  is 
boiled  for  two  hours,  filtered,  and  the  precipitate  washed  until  the 
washings  become  dark  blue.  It  is  then  dried  at  100°,  and  has  a  fine 
deep-blue  tint,  and  is  very  soluble  in  water.  Admixed  potassium  fer- 
rocyanide can  be  removed  by  washing  with  alcohol  of  40  per  cent. 
The  compound  is  precipitated  from  its  solution  by  sodium  sulphate, 
sodium  chloride,  etc.,  but  when  the  salts  are  removed  by  washing  it 
redissolves.  With  salts  of  lead,  zinc,  and  other  metals,  it  yields,  as 
Wyrouboff  observed,  a  series  of  well-defined  blue  compounds. 
Colloidal  Prussian  blue  was  obtained  by  Graham  by  dialysis.  Pure 
soluble  Prussian  blue  is  obtained  by  suspending  purified  Prussian  blue 
in  a  saturated  solution  of  oxalic  acid,  filtering,  and  allowing  the  mix- 
ture to  remain  for  two  months.  Prussian  blue  is  completely  precipi- 
tated, and  the  liquid  is  quite  colorless.  After  thorough  washing  with 
dilute  alcohol,  the  precipitate  is  readily  soluble  in  pure  water.  The 
same  result  is  obtained  in  a  very  short  time  by  precipitating  the  oxalic 
acid  solution  with  strong  alcohol  or  by  a  concentrated  solution  of 
sodium  sulphate,  and  washing  the  precipitate  with  dilute  alcohol. 
Ammonium  oxalate  or  tartrate  can  be  used  instead  of  oxalic  acid. 
If  the  oxalic  acid  solution  is  boiled,  insoluble  Prussian  blue  is  pre- 
cipitated, a  result  due  to  the  action  of  the  acid  and  not  to  the  rise  of 
temperature.  Dilute  sulphuric  acid  has  the  same  effect  at  the  ordi- 
nary temperature,  and  the  precipitate  does  not  dissolve  even  after  long 
washing.  The  soluble  and  insoluble  modifications  have  the  same 
composition. 
When  Prussian  blue  is  heated  with  water  and  molybdic  anhydride, 
it  yields  a  deep-blue  solution  which  is  not  affected  by  boiling  or  by 
gelatin.  It  is  precipitated  by  sulphuric  or  nitric  acid,  but  if  the  pre- 
cipitate, which  retains  a  small  quantity  of  molybdic  anhydride,  is  well 
washed  with  dilute  alcohol,  it  dissolves  in  pure  water.  Ammonium 
molybdate  and  tungstate  will  also  dissolve  Prussian  blue. 
When  Prussian  blue  is  treated  with  concentrated  sulphuric  acid,  it 
yields  a  soft,  white  mass  like  starch-paste,  and  if  the  temperature 
1  Compt.  rend.,  cviii,  178 — 181;  from  Journ.  Chem.  Soc,  May,  1889. 
