396 
PRUSSIAN  BLUE,  OR  HYDROCYANATE  OF  IRON. 
spoken  of  in  a  number  of  the  Journals  under  the  title  of  Dr. 
McGuigan's  Hydrocyanate  of  Iron. 
It  is  a  dark  blue  powder,  of  a  very  dull  tinge,  somewhat  grit- 
ty, and  air-dry.  It  dissolves  in  cold  or  hot  water,  leaving  be- 
hind but  a  trace  of  what  appears  to  be  dust.  Hydrochloric  acid 
dissolves  out  some  perchloride  iron,  which  on  dilution  produces 
a  finer  blue.  Caustic  Potassa  precipitates  hydrated  peroxide 
©f  iron,  the  decolorized,  or  rather  yellow  solution  containing  now 
ferrocyanide  of  potassium.  On  calcining  the  substance  at  a  low 
heat  it  gives  off  a  somewhat  empyreumatic  odor,  and  is  gradual- 
ly converted  into  a  deep  reddish  brown  powder,  which  on  being 
washed  with  water  yields  up  a  considerable  proportion  of  cyanide 
of  potassium,  or  when  the  heat  applied  has  been  too  high,  princi- 
pally carbonate  of  potassa.  The  red  powder,  if  properly  oxi- 
dized by  exposure  to  the  air  while  hot,  dissolves  completely  in 
strong  hydrochloric  acid  ;  it  sometimes  leaves  behind  a  black 
powder,  which  dissolves  in  nitro-muriatic  acid,  and  proves  to  be 
carburet  of  iron. 
The  quantitative  assay  (in  which  I  employed  altogether  the 
graduated  solution  of  Dr.  Mohr,  Fresenius,  and  Neubauer,  as 
particularly  adapted  to  this  kind  of  compounds)  gave  the  follow- 
ing results  : 
I.  One  gramme  of  the  powder,  rubbed  fine,  placed  in  a  flask 
and  dissolved  in  water,  then  decomposed  by  caustic  potash,  boil- 
ed up  and  filtered.  This  operation  was  repeated  three  times  in 
succession  with  one  gramme  each.  The  filtrate,  acidulated  and 
measured  with  permanganate  of  potassa,  showed  ; 
=0  0942  gramme  =  9  -42  p.  c.  of  Fe= 
=  01211      "      =12-11  p.  c.  ofFeO= 
=0-1816     "  =18-16p.e.ofFeCy= 
=0-7102     "      =71-02  p.  c.  of  FeCy+2KCy-f3HO  (yellow  prus 
siate.) 
=0  3633     "      =36.33  p.  c.  of  FeCy+2HCy  (ferrocyanic  acid.) 
II.  The  hydrated  peroxide  of  iron  obtained  under  I.  collect- 
ed on  the  filter,  well  washed  with  water  and  dissolved  in  hydro- 
chloric acid,  showed : 
01417  gramme  =1417  p.  c.  of  Fe= 
=0-2024     "     =20.24  p.  c.  of  Fe203= 
