PRUSSIAN  BLUE,  OR  HYDROCYANATE  OF  IRON. 
397 
III.  One  gramme  of  the  substance  was  calcined  until  con- 
verted into  a  uniform  brownish  red  powder,  placed  on  a  filter 
and  completely  exhausted  with  water,  the  filtrate  evaporated  to 
dryness,  neutralized  with  hydrochloric  acid,  calcined,  and  the 
chloride  of  potassium  thus  obtained  measured  with  a  graduated 
solution  of  nitrate  of  silver.  The  three  experiments  made  in 
this  manner  gave  : 
0-0895  gramme  =  8-95  p.  c.  of  KCI  = 
=  0  0469     "     =  4-69  p.c.  of  K  = 
=  0-1266     "     =12-66  p.c.  of  FeCy+2KCy+3Ag= 
=  0  0324     "      =  3-24  p.  c.  of  FeCy= 
=0  0648     "     =6-48  p.c.  of  FeCy-f  2HCy 
The  analysis  then  stands  : 
0  2024  grarame=  20  24  p.  c.  of  Fe203,  (peroxide  of  iron.) 
0-2984      "     =  29-84  p.  c.  of  FeCy+2HCy  (ferroejanic  acid.) 
0-1266      "     =12-66  p.  c.  of  FeCy+2KCy-f  3HO  (ferrocyanide 
of  potassium.) 
0-3726       "    =37-26  p.  c.  of  water,  partly  free,  and  in  part  held 
in  combination. 
1  0000  100  00 
This  substance  is  therefore  a  mixture  of  ferrocyanuret  and 
peroxide  of  iron,  with  ferrocyanide  of  potassium.  From  its  color, 
which  is  very  unsightly  compared  with  that  of  common  Soluble 
Blue,  I  concluded  that  it  was  not  the  precipitate  formed  by  yellow 
prussiate  in  a  protosalt  of  iron,  but  the  preparation  mentioned  in 
vol.  26  (1854),  page  504,  of  the  American  Journal  of  Pharmacy, 
and  prepared  somewhat  in  accordance  with  the  formula  there 
suggested  by  the  Editor  of  this  Journal. 
Gmelin  states :  "  On  mixing  a  solution  of  cyanide  of  pot- 
assium with  one  of  a  ferrous  salt,  a  light  reddish  brown  precipitate 
is  formed,  partly  soluble  in  acids,  the  composition  of  which  has 
not  yet  been  determined.  This  is  probably  the  true  proto- 
cyanide  of  iron,  FeCy." 
That  this  precipitate  be  free  from  potassa  is,  to  say  the 
least,  very  doubtful.  It  is  well  established  that  the  alkaline 
cyanides  immediately  on  being  brought  into  contact  with 
salts  of  iron,  form  alkaline  ferrocyanides?  or  hydrocyanates 
